I11111 111111ll Il11 Il11 IIIII IIIII III 11111 IIIII IIIII 11ll111111ll11 

US006267911B3 

(12) United States Patent (io) Patent No.: US 6,267,911 B1 

Yen et al. (45) Date of Patent: *Jul. 31,2001 

(54) PHOSPHORS WITH LONG-PERSISTENT 

GREEN PHOSPHORESCENCE 

Inventors: William M Yen, Athens, GA (US); (75) 

Weiyi Jia, Mayaquez, PR (US); Lizhu 

Lu; Huabiao Yuan, both of Athens, GA 

(US) 

(73) Assignees: University of Georgia Research 

Foundation, Inc., Atlanta, GA (US); 

University of Puerto Rico, San Juan, 

PR (US) 

(*) Notice: This patent issued on a continued prosecution application filed under 37 CFR 

1.53(d), and is subject to the twenty year 

patent term provisions of 35 U.S.C. 

154(a)(2). 

Subject to any disclaimer, the term of this 

patent is extended or adjusted under 35 

U.S.C. 154(b) by 0 days. 

(21) Appl. No.: 09/187,943 

(22) Filed: Nov. 6, 1998 

Related U.S. Application Data 

(60) Provisional application No. 601064,690, filed on Nov. 7, 

1997, and provisional application No. 601064,691, filed on 

Nov. 7, 1997. 

(51) Int. C1.7 ..................................................... C07K 11/80 

(52) U.S. C1. ..................................... 252/301.4 R; 1171946 

(58) Field of Search ...................... 2521301.4 R; 1171946 

(56) References Cited 

U.S. PATENT DOCUMENTS 

3,294,699 1211966 Lange ............................ 2521301.4 R 

4,623,816 1111986 Hoffman et al. ..................... 3131487 

5,424,006 * 611995 Murayama et al. .......... 2521301.4 R 

FOREIGN PATENT DOCUMENTS 

710709 A1 811996 (EP) . 765925 A1 211997 (EP) . 51031037 711976 (JP) . 5078659 311993 (JP) . 94029416 B2 411994 (JP) . 94029417 B2 411994 (JP) . 

OTHER PUBLICATIONS 

Katsumata et al, "Effects of Composition on the Long 

Phosphorescent SrAl204:Eu 2+, Dy3+ Phosphor Crystals", 

J. Electrochem. SOC. vol. 144, No. 9, pp. L243-L245, Sep. 

1997.* 

(List continued on next page.) 

Primary Examiner<. Melissa Koslow 

(74) Attorney, Agent, or Firm4reenlee, Winner and 

Sullivan, P.C. 

(57) ABSTRACT 

This invention relates to phosphors including longpersistence green phosphors. Phosphors of the invention are 

represented by the general formula: 

M,p.1,0,:2wEuZ+,2yR3+ 

wherein k-1-2x-2y, x is a number ranging from about 

0.0001 to about 0.05, y is a number ranging from about x to 

about 3x, M is an alkaline earth metal, and R3+ is one or 

more trivalent metal ions. Phosphors of this invention 

include powders, ceramics, single crystals and single crystal 

fibers. A method of manufacturing improved phosphors and 

a method of manufacturing single crystal phosphors are also 

provided. 

47 Claims, 15 Drawing Sheets 

2000 

- 1500 cn 

c 

3 

._ 

+ 

4 

CQ 1000 v 

=- 

v) 

K 

a, 

& 500 

-L .- 

+ 

0 

400 450 500 550 600 650 

Wavelength ( nm ) 
US 6,267,911 B1 

Page 2 

OTHER PUBLICATIONS 

Matsuzawa et al, “A New Long Phosphorescent Phosphor 

With High Brightness SrAl204:Eu 2+, Dy 3+”, J. Electrochem. SOC. vol. 143, No. 8, pp. 2670-2673, Aug. 1996.* 

Abbmscato et al. (1971), “Optical and Electrical Properties 

of SrAl,0,:Eu2+” J. Electrochem. SOC. 118(6):930-933, No 

Month. 

Autrata, R. et al. (1983), “Single-Crystal Aluminates-A 

New Generation of Scintillators for Scanning Electron 

Mocroscopes and Transparent Screens in Electron Optical 

Devices,” Scanning Electron. Microsc., pp. 489-500, No 

Month. 

Chen, R. and McKeever, S.W.S. (1997), Theory of Thermoluminescence and Related Phenomena, World Scientific, 

Singapore, pp. 1-81, No Month. 

Chemekova et al. (1977) Terzisy Dokl. Uses. Soveshch. 

Rostu. Krist. 5th 2:184-185 (Chem. Abst. (1980) 

93:85423h), No Month. 

Czochralski, J. (1918), “Ein neues Verfahren zur Messung 

der Kristallisationsgeschwindigkeit der Metalle,” Z. Phys. 

Chem. 92:219-221, No Month. 

Jia, W. (1998), “Phosphorescent dynamics in SrAl,0,:Eu2+, 

Dy3+ single crystal fibers,” J. Luminescence 76 & 

Katsumata, T. et al. (1998), “Growth and characteristics of 

long persistent SrAl,O,- and CaAl,O,-based phosphor 

crystals by a floating zone technique,” J. Cryst. Growth 

Katsumata, T. et al. (1998), “Characteristics of Strontium 

Aluminate Crystals Used for Long-Duration Phosphors,” J. 

Am. Ceram. SOC. 81:413-416. 

Katsumata, T. et al. (1997), “Effects of Composition on the 

Long Phosphorescent SrAl,0,:Eu2+, Dy3+ Phosphor Crystals,” J. Electrochem. SOC. 144(9):L243-L245. 

771424-428, 

1831361-365. 

Kutty, T.R. et al. (1990), “Luminescence of the Eu” in 

Strontium Aluminates Prepared by the Hydrothermal 

Method,” Mater. Res. Bull. 25: 1355-1362. 

Matsuzawa, T. et al. (1996), “A New Long Phosphorescent 

Phosphor with High Brightness, SrAl,0,:Eu2+,Dy3+,” J. 

Electochem. SOC. 143(8):2670. 

Palilla, F.C. et al. (1968), “Fluorescent Properties of Alkaline Eath Aluminates of the Type MAl,O, Activated by 

Divalent Europium,” J. Electrochem. SOC. 115(6):642-644. 

Pfann, W.G. (1952), “Principles of Zone-Melting,’’ Trans. 

Shionoya, S. (1998) in Phosphor Handbook, Shionoya, S. 

and Yen, W.M. (eds.), CRC Press, Inc., Boca Raton, New 

York, p. 3. 

Smets, B. et al. (1989), “2Sr0.3Al,0,:Eu2’ and 1.29(Ba, 

Ca)0,6Al,0,:Eu2’. Two New Blue-Emitting Phosphors,” J. 

Electrochem. SOC. 136(7):2119-2123. 

Tisssue, B.M. et al. (1991), “Laser-heated pedestal growth 

of laser and IR-upconverting materials,” J. Cryst. Growth 

Yen, W.M. (1995) “Preparation of single crystal fibers,” in 

Insulating Materials for Optoelectronics, F. Agullo-Lopez, 

ed., World Scientific, Singapore, Chapter 2, p. 77. 

Zlotnikova et al. (1990) Ukr. Khim Zh. (Russ. Ed.) 

56(11):1148-1151 (Chem. Abst. (1991)115:37798k). 

Zorencko, Yu.V. et al. (1991), “The Peculiarities of Receiving of Thin Film Single Crystal Oxide Luminophores,” 

Cryst. Properties and Preparation 36-38:226-233. 

AIME 1941747-753. 

1091323-328. 

* cited by examiner 
US. Patent Jul. 31,2001 Sheet 1 of 15 US 6,267,911 B1 

Fig. I 
US. Patent Jul. 31,2001 Sheet 2 of 15 US 6,267,911 B1 

I o6 

I o3 

1 10 100 I000 

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Fig. 2 
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1500 

1000 

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0 

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* 650 

Fig. 3 
US. Patent 

10000 

1000 

I00 

I 

Jul. 31,2001 Sheet 4 of 15 US 6,267,911 B1 

I I I I I "'I I 1 I I I111 I I I I1111 I I1 

I IlIlt11 9 I I I I Ill I 1 I I I Ill1 I 11 

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US. Patent 

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8000 

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Fig. 5 
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2500 

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1000 

0 

Jul. 31,2001 Sheet 6 of 15 US 6,267,911 B1 

I I I I I I I I I I 

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650 

Fig. 6 
US. Patent Jul. 31,2001 Sheet 7 of 15 US 6,267,911 B1 

# I I I I I Ill1 I 1 I I I Ill1 I I 1 11111~ I II 

10 ' I 1 1 I 1111 I I I I I I111 1 I 1 I1111 I 11 

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US. Patent Jul. 31,2001 Sheet 8 of 15 US 6,267,911 B1 

n 

tn 

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Jul. 31,2001 Sheet 10 of 15 US 6,267,911 B1 

I r I r I I 1 I I I 

I t I t I t I I I 1 

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500 

Fig. IO 
US. Patent Jul. 31,2001 Sheet 11 of 15 US 6,267,911 B1 

1 o6 

1 o5 

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a 

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Fig. I I 
US. Patent Jul. 31,2001 Sheet 12 of 15 US 6,267,911 B1 

.I 

CI 

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1 o2 

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Fig. I2 
US. Patent Jul. 31,2001 Sheet 13 of 15 US 6,267,911 B1 

- 

-c.r 

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US. Patent 

IIIl[ I I I I I Ill I 1 I I I III I ~i 

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US 6,267,911 B3 

1 

PHOSPHORS WITH LONG-PERSISTENT 

GREEN PHOSPHORESCENCE 

CROSS-REFERENCE TO RELATED 

APPLICATIONS 

This application takes priority under 35 U.S.C. §119(e) 

from U.S. provisional applications No. 601064,690, filed 

Nov. 7, 1997 and No. 601064,691, filed Nov. 7, 1997, both 

of which are incorporated by reference herein to the extent 

not inconsistent herewith. 

This invention was made at least in part with U.S. 

government funding through NASA grant MURC-NCCW0088 and NCC5-252, ARO DAAH04-96-10416 and DOE 

DE-FG02-94ER75764. The United States government has 

certain rights in this invention. 

FIELD OF THE INVENTION 

This invention relates to phosphors, particularly longpersistence green phosphorescence. The invention is also 

directed to methods of making phosphors in powder, 

ceramic and crystalline (e.g., single crystalline) form. The 

phosphors of the invention are Eu2+-activated alkaline earth 

aluminates, particularly strontium aluminates. 

BACKGROUND OF THE INVENTION 

Persistent phosphorescing materials, such as ZnS:Cu,Co, 

ZnCdS:Cu and CaSrS:Bi, have been used for many years. 

Recently a much brighter and longer persistence green 

phosphor, SrAl,0,:Eu2':Dy3' has been produced. 

Strong green luminescence from Eu2'-doped SrAI,O, 

was reported by H. Lange in Belgian patent 1,347,45 and 

U.S. Pat. No. 3,294,699. Efficient luminescence in the 

spectral range 450-520 nm was also reported from Eu2'- 

doped CaAI,O,, MgAI,O,, BaAI,O,, and SrAI,O, and their 

counterparts using alkaline earth cationic combinations. (F. 

C. Palilla, A. K. Levine and M. R. Tomkus (1986), "Fluorescence properties of alkaline earth aluminates of the type 

MAI,O, activated by divalent europium," J. Electrochem. 

SOC. 115:642). 

Long lasting and more efficient phosphorescence has 

obtained in Eu" doped SrAI,O, synthesized with excess 

alumina which results in formation of trapping centers 

associated with the Sr2' vacancy (Abbruscato et al. (1971) 

J. Electrochem. SOC. 118:930). 

Improved long persistence phosphors of certain alkaline 

earth aluminates were reported by T. Matsuzawa, Y. Aoki, N. 

Takeuchi and Y. Murayama (1996) J. Electrochem. SOC. 

143(8):2670, and in U.S. Pat. No. 5,424,006. The brightness 

and persistence time of SrAl,0,:Eu2' was improved by 

co-doping various trivalent rare earth ions to produce appropriate trapping centers. The best result was obtained by 

co-doping DY+~ with EU2+ into SrAI,O, and Nd+3 with Eu" 

into CaAl,O, to get long persistent green and purple 

emission, respectively. U.S. Pat. No. 5,424,006 also reports 

phosphors in which Mg2+ is substituted for Sr2'in 

SrA10,:Eu2', Dy3+ phosphors. 

EP published application 765,925 (Moriyama et al.) 

reports Eu2+-activated strontium aluminate phosphors in 

which part of the Sr2' of the host is replaced with Pb+3, DY+~ 

or Zn". The zinc-doped materials are reported to display 

enhanced brightness and persistence compared to 

SrA10,:Eu2', Dy3+. 

EP published application 710,709 (Murayama et al.) 

reports phosphors of matrix Ml.Jdz04.z where M is at least 

one metal selected from calcium, strontium, barium and, 

S 

10 

1s 

20 

2s 

30 

3s 

40 

4s 

so 

5s 

60 

65 

2 

optionally, magnesium, and xis a number not equal to 0. The 

matrix comprises europium and a rare earth metal, 

manganese, tin or bismuth as co-activators. 

JP Patent 76031037 (1976, Tokyo Shibaura Electric Co.) 

reports blue-emitting phosphors containing barium (or calcium or strontium)-potassium (or sodium) aluminates activated with europium and manganese. 

JP Patent 94029417 (1994, Matsushita Electronics) 

reports a strontium aluminate phosphor activated with 

europium modified by incorporation of yttrium oxide. 

JP Patent 94029416 (1994, Matsushita Electronics) 

reports a europium activated barium aluminate phosphor 

containing yttrium oxide to enhance phosphorescence. 

Zlotnikova et al. (1990) Ukr. Khim Zh. (Russ. Ed.) 

56(11):1148-1151 (Chem. Abst. (1991) 115:37798k) reports 

composition dependence of catho-luminescent properties of 

a Dy-doped SrAl,O,-Sr AI,O, system. 

T. R. Kutty et al. (1990) Mater. Res. Bull. 25:1355-1362 

report luminescence of Eu" in strontium aluminates prepared by the hydrothermal method. Blue to green luminescent phosphors of general formula Sr,AI,O,+, where nSl 

are reported. The reference also reports the preparation of 

certain aluminoborates. 

B. Smets et al. (1989) J. Electrochem. SOC. 136(7): 

2119-2123 reports blue-emitting phosphors: 

2Sr0.3AI,O3:Eu2' and 1.29 (Ba, Ca)O, 6AI,03:Eu2'. In the 

background section of the reference the authors refer to an 

earlier report of blue-green emitting phosphors 

4Sr0.7Al,O3:Eu2' and Ba04Al,03:Eu2' which could be 

synthesized only in the presence of small amounts of B,03. 

Chemekova et al. (1977) Terzisy Dokl. Uses. Soveshch. 

Rostu. Krist. 5th 2:184-185 (Chem. Abst. (1980) 

93:85423h) reports synthesis of single crystals in the calcium oxide-alumina system. Addition of Europium is said to 

produce phosphors. 

SUMMARY OF THE INVENTION 

This invention provides improved green phosphors of 

alkaline earth aluminates, particularly improved phosphors 

based on SrAl,0,:Eu2',Dy3'. Improvements in brightness 

and phosphorescence persistence are achieved by various 

co-doping schemes and/or by selective synthesis of the 

alkaline earth aluminate host using a quenching step which 

is believed to generate the host containing 0-phase (high 

temperature phase) aluminate. 

Improvements to brightness and persistence are achieved 

by doping divalent ions, Mg2+ or Zn" into the Eu2'- 

activated, trivalent metal ion-doped phosphor to replace 

AI3+ in the host. Preferably the amount of Mg2+ or Zn" 

introduced in the phosphor is substantially equivalent to the 

molar amount of trivalent rare earth metal (e.g., Dy3+). It is 

believed that this type of substitution reduces the charge 

defects induced by substitution of the trivalent rare earth ion 

sites into alkaline earth metal ion sites (e.g., Sr2' sites) in the 

aluminate. 

Improvements in phosphor properties are also achieved 

by doping monovalent alkali metal ions: Li', Na', K', Cs', 

and Rb' into the Eu2+-activated, trivalent metal ion-codoped phosphor to replace alkaline earth metal ion (e.g., 

Sr") in the host. Preferred alkali metal ions are Na' and K'. 

Preferably the amount of monovalent ion introduced into the 

phosphor is substantially equivalent to the molar amount of 

trivalent rare earth metal ion (e.g., Dy3+). It is believed that 

this type of substitution also reduces the charge defects 

induced by substitution of the trivalent rare earth ion sites 

into alkaline earth metal ion sites (e.g., Sr2' sites) in the 

aluminate. 
US 6,267,911 B3 

3 

Improvements in phosphor properties, particularly phosphor brightness, are further achieved by codoping Y3+, La+3, 

Lu-~, Gd+3 and Bi3+ into the Eu2--activated, trivalent metal 

ion-doped phosphor to replace alkaline earth metal ion (e.g., 

Sr”) in the host. Co-doping with Y+3 is more preferred. The 

amount of Y+3 that can be introduced to replace the alkaline 

earth metal ion is up to three times the molar amount of other 

trivalent rare earth metal ions (eg.,Dy3+). 

A separate aspect of this invention is the discovery that 

application of a quenching step after sintering during the 

synthesis of the alkaline earth aluminate phosphors results in 

phosphors with significantly improved properties. The phosphors produced using this quenching step exhibit improved 

brightness and longer persistence than analogous phosphors 

prepared without use of the quenching step (non-quenched 

phosphors.) 

Without wishing to be bound by any particular theory, it 

is presently believed that application of the quenching step 

to the phosphors of this invention after sintering results in 

the formation of alkaline earth aluminate phosphor at least 

in part in the high temperature phase (D-phase). Phosphor 

material prepared without such a quenching step is believed 

to be substantially in the lower temperature phase (a-phase). 

Application of the quenching step in the synthesis of 

SrAI,O, matrix phosphors is believed to generate phosphors 

containing the high temperature phase, fl-SrAI,O,. Nonquenched SrAI,O, is believed to be substantially (50% by 

weight or more) in the a-phase. The specific quenching of 

SrAI,O, is accomplished by rapid cooling of the sintered 

material from a temperature at or above about 650” C. to 

about room temperature. The 0-phase-containing phosphors 

are believed to exhibit improved phosphorescence properties. With this view in mind, preferred phosphors are those 

composed substantially of 0-phase material (i.e., greater 

than 50% by wt). More preferred are phosphors composed 

of greater than about 75% by wt. of 0-phase material. 

This invention relates to phosphors, particularly to phosphors subjected to quenching during synthesis, to phosphors 

formed as ceramics and to methods of making improved 

phosphors by application of a quenching step to retain high 

temperature phase material. 

In general, the phosphors of this invention have a variety 

of applications for the manufacture of luminous materials, 

night vision apparatus and in optoelectronic devices. 

This invention also provides single crystal phosphors with 

long persistence times. The crystals have a general formula 

MAI,O,, where M stands for Sr, Ca, Ba or a combination of 

Sr, Ba, or Ca. These materials are doped with Eu” as an 

activator, and co-doped with Dy3+, Nd3+, or other trivalent 

rare earth ions or Bi3+ (most generally R3+) or combinations 

of these ions. The trivalent metal ions are believed to act as 

trapping centers. The single crystal phosphors can also be 

prepared from MAI,O,:EU~+, R3+ in which Mg2+or Zn” are 

substituted for AI3+ or in which Na+ or K+ (or other alkali 

metal ions) are substituted for M2+ as charge compensators. 

These crystals phosphoresce at wavelengths of 520 nm 

(SrAl,0,:Eu2-,Dy3+) or 440 nm (CaAl,0,:Eu2+,Nd3+) with 

persistence times longer than about 15 hours. 

The single crystals of this invention have direct application to the manufacture of phosphorescent jewelry and 

related items for ornamentation or apparel. In addition, due 

to their strong phosphorescent properties, the crystals can 

have important applications in optoelectronic technology, 

such as in image storage and in memory devices. 

The oxide phosphors of this invention are chemically 

stable and believed to represent no significant hazard to the 

environment. 

4 

BRIEF DESCRIPTION OF THE DRAWINGS 

FIG. 1 illustrates the luminescent spectra of (a) 

0-SrAI,O4:O.02 Eu2+, 0.02 Dy3+ and the corresponding 

a-phase material (b). In the Figures, the term fl-SrAI,O, (or 

0-phase material) refers to phosphors subjected to quenching as described in the Examples, and the term a-SrAl,O, 

(or a-phase material) refer to phosphors not subjected to 

quenching during synthesis. 

FIG. 2 is a graph of the decay curves of the afterglow of 

0-SrAI,O4:O.02 Eu2+, 0.04 Dy3+ (a) and the corresponding 

a-phase material (b). 

FIG. 3 illustrates the luminescence spectra of 

SrAI,O,:O.Ol Eu2+, 0.02 Dy3+, (b) and the corresponding 

1s phosphor with 2 mol % Mg2+ substituted for AI3+ (a) 10 

seconds after exposure to a 13 W fluorescent lamp. 

FIG. 4 is a graph of decay curves of the after-glow of 

SrAI,O,:O.Ol Eu2+, 0.02 Dy3+ (b) and the corresponding 

phosphor with 2 mol % Mg2+ substituted for AI3+, (a). 

FIG. 5 illustrates the excitation spectra of samples of 

SrAI,O,:O.Ol Eu2+, 0.02 Dy3+ (b) and the corresponding 

phosphor with 2 mol % Mg2+ substituted for AI3+. 

FIG. 6 illustrates luminescent spectra of 

SrAI,0,:0.02Eu2+, 0.04Dy3+ (b) and the corresponding 

phosphor with 4 mol % Zn2+ substituted for AI3+, (a). 

FIG. 7 is a graph of decay curves of the after-glow of 

SrAI,0,:0.02Eu2+, 0.04Dy3+ (b) and the corresponding 

phosphor with 4 mol % Zn substituted for AI3+, in the first 

FIG. 8 illustrates luminescent spectra of the after-glow of 

SrAI,0,:0.02Eu2+, 0.04Dy3+ (b) and the corresponding 

phosphor with 4 mol % Na+ substituted for Sr2+ (a). 

FIG. 9 is a graph of decay curves of the after-glow of 

35 SrAI,0,:0.02Eu2+, 0.04Dy3+ (b) and the corresponding 

phosphor with 4 mol % Na+ substituted for Sr”. 

FIG. 10 illustrates the excitation spectrum of 

SrAI,0,:0.02Eu2+, 0.04Dy3+ with 4 mol % Na’ substituted 

for Sr2+ (monitoring at 520 mn). 

FIG. 11 is a graph of the decay characteristics of the 

phosphorescence of the single crystal (a) after exposure to a 

13 W fluorescent lamp. The decay curve of a commercial 

green phosphor ZnS:Cu (b) is also shown and the threshold 

of eye-sensitivity is indicated (c). 

FIG. 12 is a graph of the decay characteristics of the 

phosphorescence of the single crystal SrAI,0,:0.02 Eu2+, 

0.04Dy3+ with 4 mol % Mg2+ substituted for AI3+ after 

exposure to a 13 W fluorescent lamp. 

FIG. 13 is a graph of the decay characteristics of the 

phosphorescence of the single crystal SrAI,O,:O.Ol Eu2+, 

0.04Dy3+ with 4 mol % Na’ substituted for Sr2+ after 

exposure to a 13 W fluorescent lamp. 

FIG. 14 is a graph of the decay characteristics of the 

55 phosphorescence of the single crystal CaAI,O,:O.Ol Eu2+, 

0.01 Nd3+ after exposure to a 13 W fluorescent lamp. The 

threshold of eye-sensitivity is indicated (dashed line). 

FIG. 15 is a graph of the decay characteristics of the 

mixed single crystal Sro,,,Bao,,,Al,03:0.01Eu2’, 0.01 Dy3+ 

60 after exposure to a 13 W fluorescent lamp. 

5 

2o 

25 

3o 60 minutes after exposure to a 13W fluorescent lamp. 

40 

45 

DETAILED DESCRIPTION OF THE 

INVENTION 

This invention relates to long-persistence green phos65 phors. Several basic physical factors should be considered in 

developing such phosphors. Phosphors of this invention are 

based on addition of an activator (an emitter) to a host 
US 6,267,911 B1 

5 6 

matrix. The host (or matrix) and activator are selected to 

provide the desired color (dependent upon the wavelength of 

emission) and high quantum efficiency. The energy of the 

localized ground state of the activator should be well above 

the valence band of the host to allow persistent phospho- s 

rescence to occur. 

The hosts of this invention are alkaline earth aluminates 

MN,O, (where M is an alkaline earth or mixture of alkaline 

earths, e.g., Sr, Ca and/or Ba) The activator employed in the 

phosphors of this invention is Eu". 

Persistent phosphorescence was discovered in the 11th 

century in China and Japan and in the 16th century in Europe 

(Shionoya, S. (1998) in Phosphor Handbook, Shionoya, S. 

and Yen, W. M. (eds.), CRC Press, Inc., Boca Raton, N.Y., 

p. 3). The phenomenon involves two kinds of active centers: 

Phosphors of this invention have the general formula: 

where is 1-2x-2y; can range from about o.oool to about 

0.05 and is preferably about 0.001 to about 0.02; y can range 

from about 0.0001 to about 0.15 and is preferably equal to 

2x; M is most generally an alkaline earth metal, but is 

preferably Sr or a mixture of Sr with Ca, or Ba or both Ca 

and Ba; R is generally one or more trivalent metal ions, but 

is preferably a trivalent metal ion selected from the 

lo group:Pr3+, Ho3+, Nd3+, Dy3+, Er3-, La3+, Lu3+, Ce3+, Y3+, 

Sm3+, Gd3+, n3+, Tm3+, n3+, Bi3+ and combinations 

thereof. The preferred trivalent metal ion dopant is Dy3+ or 

its 

MA~,O,:~~EU~+, 5~~' 

with y3+. 

not wishing to be bound by any 

1s theory, it is believed that long persistence time in the 

activated matrix phosphors of this invention is obtained by emitters and traps. The phosphorescent dynamics are 

plex and many aspects remain creating proper trapping centers in the matrix, Such trapping 

centers can store excitation energy and release it gradually Thennoluminescence 

and photostimulable phosphorescence are physically gov- to the emitter, 

erned by mechanisms similar to Persistent PhosPhorescence 2o Doping of trivalent metal ions, particularly trivalent rare 

(Chen R and McKeever, s. w. s. (199712 Theory of Ther- earth metal ions and the Group VA metal ion Bi3+, into the 

mohminescence and Related Phenomena, World Scientific, host matrix of this invention results in improved phosphoSingapore; Sonoda, M. et al. (1983) Radiology 148:833). rescence brightness and persistence time. Dopants for creThe main difference between these three phenomena appears ating trapping centers include trivalent rare earth metal ions: 

to be the depth of traps. When a phosphor possesses centers Pr3+, Ho3+, Nd3+, Dy3+, Er3+, La3+, Lu3+, Ce3+, Y3+, Sm3+, 

with certain trapping depth which can be effectively acti- 25 Gd3+, Tb3+, Tm3+, and Yb3+ and tlivalent Bi. 

vated at room temperature, it will show persistent phospho- This invention demonstrates that energy efficiency, the 

rescence. Deeper trapping centers can be activated by heat- brightness and the Persistence time of PhosPhors are 

ing or photostimu~ation, Therefore, a study of improved by addition of charge compensators to the host 

phosphorescence dynamics allows the characterization of matrix. In addition the use of charge compensators reduces 

phosphors facilitate studies of phosphorescence dynamics, ous defects, such as color centers, which will reduce or kill 

luminescence. Phosphors of this invention include those in 

The traditional persistent phosphors are sulfides, zns, which a portion of N3+ in the host is replaced with divalent CdS, Cas and SrS, and their mixed crystals. dl of these ions, such as ~~2+ or zn2+ and those in which a portion of 

compounds have high vapor Pressure, and it has generally 35 the alkaline earth metal ion (M") is replaced with a 

been difficult to grow crystals from the melt. monovalent alkali metal ion, such as Li', Na+, K+, Cs+ or 

Phosphor materials of this invention can exhibit enhanced Rb'. These monovalent and divalent ions are believed to act 

phosphorescence intensity and/or long persistence of phos- as charge compensators. 

phorescence. Preferred phosphors of this invention have This invention specifically exemplifies phosphors in powintensity enhanced (as measured in a similar measurement 40 der or ceramic form prepared by combining the host, actisystem) compared to a standard commercial sample of ZnS vator and trivalent metal ion dopants with a flux material. 

phosphor. Persistence of phosphorescence is measured The flux is, however, optional in these formulations. The 

herein as persistence time which is the time after discon- flux material of most interest is B,03. In the phosphors of 

tinuing irradiation that it takes for phosphorescence of a this invention flux is used to improve solid state chemical 

sample to decrease to the threshold of eye sensitivity. This 45 reaction. The phosphors of this invention can be made by the 

threshold is the signal level of emission intensity that a following general method. Phosphor components are comnaked (i.e., unaided) eye can clearly see in the dark. Per- bined as indicated in stoichiometric formulas (with or withsistence times are assessed by following phosphorescence out a flux). The mixture is treated to form a homogeneous 

intensity as a function of time. Clearly measurement com- fine powder, for example by milling or grinding. The powder 

parisons of persistence times must be performed under SO is preferably pressed into pellets. The powder or pellets are 

identical conditions using the same detection systems. The prefired at temperatures between about 600 to 800" C. 

term "persistent phosphors" has been applied to materials (dependent upon the phase transitions of the material) in air 

exhibiting phosphorescence lasting from minutes to hours. for about 1-2 hrs. The prefired material is again treated to 

The term "long-persistent phosphor" historically has been form a fine homogeneous powder (e.g., milling, grinding, 

used to refer to ZnS:Cu, CaS:Eu, Tm and similar materials ss pulverizing) suitable for sintering. Preferably, the powder is 

which have a persistence time of 20 to 40 minutes. Materials pelleted before sintering. The powder or pellets are the 

herein can exhibit persistence time up to about 16-18 hrs or sintered at about 1 300" C. under a reducing atmosphere, 

more. It is generally the case that phosphors having longer e.g., HJN, having 2-5% by volume H,. 

persistence times are more preferred. Preferred phosphor B,03 can be replaced in all formulations of this invention 

materials, including single crystals and single crystal fibers, 60 by an amount of H3B03 sufficient to provide an equivalent 

of this invention can exhibit phosphorescence persistence molar amount of B (i.e., 2H3B03 replace each B,03). 

times of greater than about 3-5 hrs. More preferred phos- This invention is based at least in part on the finding that 

phors exhibit persistence times greater than about 10-12 hrs. the method of synthesis of the host materials, e.g., the 

Most preferred phosphors exhibit persistence times of alkaline earth aluminates, can be an important factor in 

greater than about 15-18 hrs. Persistence times of ceramics 65 obtaining phosphors with improved persistence and brightcan be longer or shorter than those of single crystals of the ness. Application of a quenching step to rapidly cool sintered 

same materials. material from the sintering temperature to lower temperathese three important luminescence processes. Single crystal 30 the Occ~rrence of quenching centers originating from vari- 
US 6,267,911 B3 

7 

tures (e.g. to room temperature) is found to produce phosphor material with improved phosphor properties. In 

particular, application of an air quenching step to the sintered alkaline earth aluminates of this invention results in an 

improved phosphor material. More specifically, the alkaline 

earth aluminate is optionally cooled to an intermediate high 

temperature between about 650" C. and about 750" C. and 

then quenched by removing the material to a room temperature environment (air quenching). 

Materials specifically exemplified herein are intially 

cooled from the sintering temperature to an intermediate 

high temperature for practical reasons to avoid thermal 

shock breakage of the ceramic container or the sintering 

chamber during synthesis. Rapid quenching of the material 

from the sintering temperature, if practical, would be preferred to ensure formation of improved phosphor materials. 

Materials specifically exemplified herein are quenched in 

air, i.e., taken from a furnace an placed in a room temperature environment. Air quenching is simply a convenient way 

of achieving the desire rapid cooling. It is not necessary to 

quench the materials to room temperature. Suitable materials can be made by quenching to a temperature somewhat 

above room temperature (e.g., less than or equal to about 

100" C.) Alternatively, materials may be quenched by rapid 

cooling in water, ice or by using coolants, including dry ice, 

liquid nitrogen, etc. 

It is presently believed that the quenching step applied to 

alkaline carth aluminate phosphors facilitates formation of 

high temperature phase material at temperature substantially 

lower than the phase transition temperature (e.g., at room 

temperature). For example, SrAl,O, undergoes a phase 

transition at 650" C. between a high temperature 0-phase 

and a lower temperature a-phase. The crystal structure of the 

high temperature phase, fl-SrAl,O,, is hexagonal. The structure of the room temperature phase, a-SrAl,O,, is monoclinic. The optional intennediate cooling step applied in 

exemplified phosphor materials cools the materials to a 

temperature above the phase transition temperature (greater 

than or equal to 650" C.). Materials held at the intermediate 

temperature (above the phase transition temperature) are 

rapidly cooled (quenched). Quenched alkaline earth aluminates are believed to comprise at least in part 0-phase 

alkaline earth aluminate. 

Eu2+-activated SrAl,O, phosphors prepared using a 

quenching step are demonstrated herein to provide better 

phosphorescent performance than phosphors prepared using 

the corresponding non-quenched, presumably substantially 

a-phase material. Quenched-SrAl,O, co-doped with Eu3' 

and trivalent metal ions, particularly trivalent rare earth 

metal ions, exhibit much brighter and longer phosphorescence than the corresponding non-quenched phosphors. 

fl-SrAl,O, green phosphors can be synthesized using a 

quenching step in the sintering cycle. The quenching method 

can be employed to synthesize SrAl,O, phosphors containing 0-phase material activated with Eu" and doped with 

trivalent metal ions as well as those phosphors containing 

0-phase material in which divalent and monovalent ions are 

substituted into the matrix. 

Charge compensators can be included in either 

o(quenched)- and a(non-quenched)-SrAlz04 to reduce the 

number of phosphorescence quenching centers existing in 

these materials. In both matrices, AI3+ is situated in tetrahedral sites and Sr in octahedral sties. Doping trivalent rare 

earth into the SrAl,O, lattice through substitution of Sr2' 

generates lattice defects associated with interstitial oxygen; 

these defects are known to be phosphorescence killers. 

Co-doping divalent ions, such as Mg2+ or Zn2+ to replace 

8 

part ofA13', or co-doping monovalent alkali metal ions, such 

as Na' or K', to replace a portion of Sr2+, eliminates these 

oxygen defects and improves the brightness of the phosphors. 

Preferred phosphors of this invention are those having a 

SrAl,O, matrix. A portion of the Sr2' in the matrix can, 

however, be replaced with Ca", Ba2' or both without 

significant shift in emission wavelength. 

The basic phosphors of this invention are most generally 

io prepared by admixing the components in the following 

s 

molar proportions: 

(1-2w-2y)MC03+A1,03+xEu,0,+yR,0,+zB,0, (optional) 

and will have the general stoichiometric formula: 

15 

~di,0,:2w~u~+, 2y~3+ 2 

where k=1-2x-2y, x is a number ranging from about 0.0001 

to about 0.05 and is preferably about 0.005 to about 0.02, y 

can range from about 0.0001 to about 0.15 and is preferably 

20 equal to 2x. M is most generally an alkaline earth metal, but 

is preferably Sr or a mixture of Sr with Ca, Ba or both. R is 

generally one or more trivalent metal ions, but is preferably 

a trivalent metal ion selected from the group:Pr3', Ho3+, 

Nd3+, Dy3+, Er3+, La3', Lu3+, Ce3', Y3+, Sm3', Gd3+, Tb3+, 

25 Tm3', Yb3+ and Bi3+. The preferred trivalent metal ion 

dopant is Dy3+. 

The combined phosphor components are milled or ground 

into a homogeneous fine powder, optionally pressed into 

pellets and prefired in air (or other oxygen-containing gas) 

30 for about 1 hr at about 600" C. The prefired material is 

remilled or ground into a fine powder for sintering. The 

powder is optionally pressed before sintering. The material 

is sintered at about 1300" C. for one hour in a reducing 

atmosphere. After the material is sintered it is cooled. The 

35 method of cooling employed determines if high temperature 

phase @-phase material) or the lower temperature (a-phase 

materia1)is produced. 

To form a high temperature phase material, the sintered 

material is optionally slowly cooled to an intermediate 

40 temperature: about 650" C. to about 750" C., preferably to 

about 700" C. and held at that temperature for a few minutes. 

This step minimizes thermal shock to equipment. The material is then rapidly quenched to room temperature. Through 

this quenching process at least part of the material remains 

45 in the high temperature phase at room temperature. 

To form the low temperature phase material, the sintered 

material is slowly cooled to room temperature. 

Quenched phosphors of formula M&,0,:2xEu2', 2yR3- 

are generally improved in brightness and persistence comSO pared to the analogous non-qucnched phosphors. For 

example, phosphor-containing quenched SrAl,0,:0.01Eu2', 

0.02Pr3' exhibits a 50% improvement in brightness compares to the corresponding non-quenched material. 

Phosphors of this invention include those in which two 

ss trivalent metal ions are doped into the matrix and have the 

general stoichiometric formula: 

M~l,0,:2wE~~+, 2y,RI3-, 2y,Rz3+, 

where k=1-2x-2y, y1+y2=y, R, and R, are at least two 

60 different trivalent metal ions, and M being defined above. 

Either R, or R, may represent a mixture of different trivalent 

metal ions. The number x can range from about 0.0001 to 

about 0.05 and is preferably about 0.005 to about 0.02, y can 

range from about 0.0001 to about 0.15 and is preferably 

65 equal to 2x. Phosphors in which R, is DY+~ and R, is Y'3 

are preferred. Phosphors of this formula include both 

quenched and non-quenched material. 
US 6,267,911 B3 

9 

The phosphors of this invention include those in which 

AI3+ in the host is substituted by a divalent metal ion, 

particularly Mg2+ or Zn". These phosphors have the general 

formula: 

M@.l,-,O,.qXO: 2wEuZf, 2yR3', 

where k=1-2x-2y, x can range from about 0.0001 to about 

0.05 and is preferably about 0.005 to about 0.02, y can range 

from about 0.0001 to about 0.15 and is preferably equal to 

2x. X is a divalent metal ion, preferably Mg2+ or Zn2+ and 

q can range from about equal to 0.0001 to about equal to 

0.45. The amount of divalent ion (9) added to the matrix to 

replace AI3+, is preferably about equal to the amount of R+, 

doped into the matrix (i.e., q preferably=2y). Phosphors of 

this formula include both quenched and non-quenched materials. 

The phosphors of this invention include those in which 

M2+ in the host is substituted by a monovalent metal ion, 

particularly Na+ or K+. These phosphors have the general 

formula: 

~di,0,.r~,0:2w~u~+, 5~3+, 

where k=1-2x-2y-2r, x can range from about 0.0001 to about 

0.05 and is preferably about 0.001 to about 0.005, y can 

range from about 0.0001 to about 0.15 and is preferably 

equal to 2x. Z is a monovalent alkali metal ion, preferably 

Na' or K+, and r can range from about equal to or more than 

0 to about 0.30. (The amount of monovalent ion (2r) added 

to the matrix to replace M2+, is preferably about equal to the 

amount of R+, doped into the matrix (i.e., r preferably=y). 

Phosphors of this formula include both quenched and nonquenched material. 

The phosphors of this invention can be prepared as 

powders or ceramics as indicated in the examples. Materials 

of this invention can bc used to prepare single crystal 

phosphors as described in Example 5. In preparation of 

single crystal phosphors the addition of flux (B,O, or boric 

acid) is optional. The quenching step discussed above is also 

optional when making single crystals or single crystal fibers. 

Sintered phosphor material can be used to grow single 

crystals or single crystal fibers. Any crystallization technique can be employed. The laser heated pedestal method is 

preferred. Sintered pellets are cut into bars to introduction 

into the crystal growth chamber (1x1 mm/1.5'1.5 mm 

pieces). The bars are carefully cleaned prior to introduction 

into the chamber which is filled with an non-reactive or inert 

gas (e.g., N,) or a somewhat reducing gas (cabout 1% by 

volume H, in N,). Care should be take to minimize or avoid 

reoxidation of Eu" ions and to minimize or avoid reduction 

to the monovalent or zero valent (i.e., metal) state. Other 

metals in the materials preferably remain in the same 

oxidation state during crystallization. Apointed ceramic bar 

can be used as a "seed" to stimulate spontaneous nucleation 

in the LHPG process. It was observed that the initial part of 

the fiber prepared by the LHGP process was a twined crystal. 

the fiber eventually becomes one single crystal after a 

transition stage, but the crystal is not oriented. Fiber lengths 

of single crystals grown are variable, but can be as long as 

several centimeters in length. Single crystals with an average 

diameter of about 0.8 mm can be grown. 

Transparent, greenish single crystal fibers of SrAl,O,:Eu, 

Dy were obtained from sintered phosphor prepared by 

combined components: 0.94 SrCO, (99.95%), A1,0, 

(99.95%), O.OlEu,O, (99.9%), and 0.02 Dy,O, (99.9%). 

Transparent, purplish single crystal fibers of CaAl,O,:Eu, 

Dy were obtained from sintered phosphor prepared by 

S 

10 

1s 

20 

2s 

30 

3s 

40 

4s 

so 

5s 

60 

65 

10 

combined components: 1.05 CaCO,+Al,0,+0.01 Eu,O,+ 

0.02 Nd,O,. Since the first crystalline phase obtained on 

cooling is CaAI,O,. To ensure that the crystal was CaAl,O,, 

1.6% excess of CaCO, was added to the initial component 

mixture. It was found that incongruent melting was not a 

problem for crystal growth by the LHPG method and high 

quality crystals could be obtained from the stoichiometric 

melt. After the first phase CaAI,O,. is crystallized, the melt 

gradually becomes CaO rich, the composition changes to 

one where the first phase of CaAI,O, is stable and CaAI,O, 

starts to form. 

For the preparation of CaAI,0,:EU2+,Dy2+ single crystal 

phosphors inclusion of an excess of CaCO, over the 

required molar proportions to obtain the desired stoichiometry is preferable to ensure formation of the CaAI,O, phase, 

especially when growing single crystals by the Czochralski 

method. The excess is not necessary when growing single 

crystals by the floating zone or LHPG methods. 

At low temperature the photoexcitation energy can be 

stored in the phosphor sample for a long time. For example, 

single crystal material SrAl,0,:Eu2+, Dy3+ irradiated at 

room temperature and kept at liquid nitrogen temperature 

(about -178" C.) for ten days, still exhibits bright after-glow 

after it is warmed back up to ambient temperature. 

The phosphors of this invention in powder, ceramic or 

single crystal form have a variety of applications for the 

manufacture of luminous materials, including paints, inks, 

plastic articles, toys, jewelry, ornaments and apparel. The 

phosphors have application in night vision apparatus and in 

optoelectronic devices. The phosphors of this invention can 

for example be employed in detection of UV radiation and 

the manufacture of infrared detectors and beam finders. 

A. A phosphor material comprising a 0-phase phosphor of 

More specifically this invention provides: 

formula: 

~di,0,:2w~u~+, 5~3+ 

where: 

M is an alkaline earth element selected from Sr, Ca, or Ba 

k is 1-2x-2y; 

x is a number ranging from about 0.0001 to about 0.05; 

y can range from about 0.0001 to about 0.15; and 

R3+ is one or more trivalcnt metal ions selected from the 

group Pr3+, Ho3+, Nd3+, Dy3+, Er3+, La3+, Lu3+, Ce3+, 

Y3+, Sm3+, Gd3+, Tb3+, Tm3+, Yb3+ and Bi3-. 

Preferred phosphors of paragraph A are those with M=Sr 

and/or those wherein y=2x. Phosphor material of paragraph 

A includes phosphors in which R3+ is a mixture of at least 

two trivalent rare earth metal ions and particularly those 

phosphors where R3+ is a combination of Dy3+ and Y3+. 

B. Phosphor materials of paragraph Awhich also contain up 

to about 2y moles of Mg2+ substituted for AI3+, up to 

about 2y moles of Zn" substituted for AI3+, up to about 

2y moles of Na+ substituted for M2+, or up to about 2y 

moles of K+ substituted for M2- in said formula. 

or combinations thereof; 

C. Phosphor material having the general formula: 

~di,0,:2w~u~+, 5~~' 

where: 

M is an alkaline earth element selected from Sr, Ca, or Ba 

k is 1-2x-2y; 

x is a number ranging from about 0.0001 to about 0.05; 

y can range from about 0.0001 to about 0.15; 

or combinations thereof, 
US 6,267,911 B1 

11 12 

R3+ is one or more trivalent metal ions sclected from the h. quenching said sintercd material to a temperature 

group Pr3+, Ho3+, Nd3-, Dy3+, Er3+, La3+, Lu3+, Ce3+, Y3+, below 650" C. such that at least a portion of the material 

Sm3+, Gd3-, Tb3+, Tm3+, Yb3+ and Bi3+; and remains in the 0-phase. 

which also contains up to about 2y moles of a divalent In this method, the sintered material is Preferably 

metal ~~2+ or zn2+ substituted for p~3+ in the formula or up 5 quenched from the sintering temperature to a temperature 

to about zY moles of a monovalent metal ~i+, N~+, K+, below about 100" C. and conveniently is quenched to about 

Cs' or Rb' substituted for Sr2+ in the formula. room temperature. An optional intermediate cooling step can 

Preferred phosphor materials of paragraph are those be applied to the sintered material to cool the material to an 

where the divalent or monovalent ion is present in the intermediate high temperature at or above the phase transiphosphor in an amount equal to that of R3+, Preferred tion temperature of the material. The material is then 

phosphors of paragraph are those wherein R3+ is Dy3+ or quenched from the intermediate high temperature to a tema of Dy3+ and y3+, phosphor material of claim perature below about 100" C. and conveniently is quenched 

moles of Mg2+ substituted for ~3+ in said formula, Phos- applied in general to rapidly cool the sintered material in a 

containing up to about 2y moles of Znz+, substituted for the transition temperature between the high and low temd3+, in the formula, up to about 2y moles ofNa+ substituted perature phase such that at least a portion of the material is 

substituted for M2+in the formula. In the following examples, phosphor materials syntheand phosphor materials synthesized without a quenching 

step are designated a-phase materials. 

EXAMPLES 

10 wherein said phosphor further comprises up to about 2y 

phor materials of paragraph C include phosphors further 1s high temperature phase to a temperature substantially 

to room temperature. The quenching step is preferably 

for M2+, in the formula, up to about 2y moles of K+ 

D, Asingle crystal phosphor material containing a phosphor 20 sized with a quenching step are designated O-phase 

retained in the high temperature phase. 

of the formula: 

M~~,o,:z~E~z+, 5~3+ 

where: Example 1 

M is an alkaline earth element selected from Sr, Ca, or Ba 2s Preparation of Improved SrAl,0,:Eu2+, R3+ Green phosk is 1-2x-2y; This method can be used to prepare all improved phosx is a number ranging from about 0.0001 to about 0.05; Phors of host formula MA1204 activated with EU2' and 

3o doped with a trivalent metal ion, e.g., a trivalent rare earth 

metal ion, or the Group VA trivalent Bi ions, where M is Sr R3+ is one or more trivalent metal ions selected from the or a mixture of Sr with Ca, Ba or both. The method also 

phors where Zn2+ and Mg2+ are substituted for AI3+ as 

charge compensators into the host. The method applies as 

well to preparation of improved MAI,O, host phosphors 

where Na+ and K+ are substituted for Sr2+ or other M2+, in 

the host matrix as charge compensators. 

The phosphor components are combined according to the 

desired molar proportions, as will be discussed in more 

detail below. The resultant mixture is milled or ground into 

a homogeneous fine powder for prefiring. The powder is 

preferably pressed into pellets under 1.3 ton/cm2 pressure. 

The powder or the pressed pellets are prefired at about 600" 

C. in air for about one hour. The prefired material is then 

pulverized and milled again into a fine powder suitable for where: sintering. Before sintering the powder can again be pressed 

M is an alkaline earth element selected from Sr, Ca, or Ba into ceramic pellets under 1.3 ton/cm2 pressure. 

The powder or the pressed pellets are sintered at about 

k is 1-2x-2y; 1,300' C. for about one hour in a H,N, flowing gas mixture 

x is a number ranging from about 0.0001 to about 0.05; (i.% a reducing atmosphere) containing 2-5'32 HZ by volume 

y can range from about 0.0001 to about 0.15; and at a flow rate of about 0.1 liter per minute. The sample is 

R3+ is one or trivalent metal ions selected from the then slowly cooled to a temperature between about 650" C. 

to about 750" C., preferably to 700" C., preferably at a rate 

Nd3+, Dy3+, Er3+, La3+, Lu3+, Ce3+, y3+, Sm3+, Gd3+, ss of about 100" C. to about 500" C. per hour, and thereafter 

quickly quenched to room temperature by pulling the container entirely out of the furnace (air quenching). At least b. processing said combined components to produce a fine 

part of the MAI,O, phosphor is believed to remain in its 

high temperature 0-phase through this quenching process. c. optionally pressing said fine powder into pellets; The high temperature 0-phase of SrAI,O, is hexagonal in d. prefiring said powder or pellets in an oxygen- 60 

which is monoclinic. 

Example 2 

Preparation of Low Temperature a-Phase MAI,O,:EU~' 

This method can be used to prepare all low temperature 

phase phosphors of host formula MAI,O, (where M is Sr or 

or combinations thereof, phors 

is a number ranging from about to about 3x; and 

group pr3+2 Ho3-2 Nd3+2 Dy3+2 Er3+2 La3'2 Lu3+2 Ce3'2 applies to the preparation of improved Md,O, host phos- Y3+, Sm3+, Gd3+, Tb3+, Tm3+, Yb3+, and Bi3+. 

Phosphor material of paragraph D also include those 

which contain up to about 2y moles of Mg2+ substituted for 35 

AI3+ in the formula, up to about 2y moles of Zn" substituted 

for AI3+, in the formula, up to about 2y moles of Na+ 

substituted for M2+ in the formula, or up to about 2y moles 

of K+ substituted for M2+ in the formula. 

an improved phosphor which comprises the steps of 

equation: 

The invention specifically provides a method for making 40 

a. combining phosphor components according to the 

( l-2w-2y)MC03+Al,03+xEu,0,+yR,0, 4s 

or combinations thereof; 

so 

group Pr3+, HO~+, 

Tb3+, Tm3+, Yb3+, and Bi3+; 

powder; 

containing gas for about 1 hour at a temperature of about to the lower temperature a-phase Of SrA1204 

600" C; 

powder; 

e. processing said prefired material to produce a finc 

f. optionally pressing said fine powder into pellets; 

g. sintering said powder or pellets of steps e or f at about 

65 Green Phosphors 

1300" C. for one hour in a reducing atmosphere; 
US 6,267,911 B3 

13 a mixture of Sr with Ba and/or Ca) doped with Eu" as an 

emitter, and codoped with trivalent metal ions, including 

rare earth metal ions and Group VA Bi3+. The method is 

exemplified for preparation of a-phase SrAI,O, phosphors. 

This method also applies to the preparation of lowtemperature phase MAI,O, host phosphors where Zn2+ and 

Mg2+ are substituted for AI3+ as charge compensators and to 

low temperature phase MAI,O, host phosphors where Na+ 

and K+ are substituted for Sr2+ as charge compensators. 

The phosphor components are combined according to the 

desired molar proportions. The resultant mixture is milled or 

ground into a homogeneous fine powder for prefiring. The 

powder is preferably pressed into pellets under 1.3 ton/cm2 

pressure. The powder or the pressed pellets are prefired at 

about 600" C. to about 800" C. in air for about one to two 

hours. The prefired material is then pulverized and milled 

again into a fine powder suitable for sintering. Before 

sintering the powder can again be pressed into ceramic 

pellets under 1.3 ton/cm2 pressure. 

The powder or the pressed pellets are sintered at about 

1,300' C. for about one to two hours in a H,N, flowing gas 

mixture containing 2-5% H, by volume at a flow rate of 

about 0.1 liter per minute. The sample is then cooled to room 

temperature at a rate of about 100" C. to about 500" C. per 

hour. a-SrAl,O, phosphor is obtained through this process. 

Example 3 

Preparation of 0-Phase SrAl,O,:Eu, R where R is a Trivalent 

Rare Earth Ion or Bi3+ and Comparison with an Analogous 

a-Phase Phosphor 

For preparation of the 0-phase green phosphors SrAI,O,: 

Eu, R components are mixed in the following molar proportions: 

( l-2w-2y)SrC0,+Al,0,+xEu~03+yR~03+zB~03 

where x=about 0.0001 to about 0.05; 

y=x to 2x; 

z=o to 0.1; 

R is a trivalent rare earth or Bi3+; and 

B,03 optionally is used as a flux in this preparation and 

can be replaced with two molar equivalents of H3B03. 

The components are mixed and treated as indicated in 

Example 1 to obtain the 0-phase phosphor. 

The synthesis is exemplified by the synthesis of 0-phase 

and a-phase SrAI,O,:O.Ol Eu, 0.02Dy. Phosphor components were combined in the following molar proportions: 

0.97 SrCO,+A1,0,+0.005 Eu,O,+O.Ol Dy,O,+O.l B,O, 

The mixture was divided into two parts. One part (labeled 

as a-SAO-ED for a-SrAl,O,) was processed as indicated in 

Example 2, and the other part (labeled as 0-SAO-ED for 

fl-SrAI,O,) was processed as indicated in Example 1. 

Green phosphor prepared by the two different methods 

exhibited properties as indicated in Table 1. Table 1 provides 

after-glow intensity measurements of the 0-phase material 

relative to the a-phase material (the reference). 

FIG. 1 illustrates the luminescent spectra of (a) fl-SrAI,O, 

phosphor (0-SAO-ED) and(b) a-SrAl,O, (a-SAO-ED) 10 

sec. after exposure to a 13 W fluorescent lamp. The luminescent spectrum of the 0-phase is similar to that of a-phase, 

but shifted to the long wavelength side by about 3 nm. FIG. 

2 shows decay curves of the after-glow of 

~-SrAl,0,:0.01Eu2+0.02 Dy3+ (a) and the corresponding 

a-phase material (b) (after exposure to a 13 W fluorescence 

lamp). It can be seen that the brightness of 0-phase of the 

phosphor is about 50% better than that of a-phase. 

14 

TABLE 1 

Comparison of phosphorescence between fi-SrAl,O, phosphor 

(fi-SAO-ED) and a-SrAl,O, (aSAO-ED), at indicated 

times after exposure to a 13 W fluorescent lamp. 5 

Time (mid after 

Sample: 1 10 30 60 

10 a-SAO-ED 100 100 100 100 

fi-SAO-ED 159 149 147 146 

Example 4 

15 Charge Compensation in a-MAl,O,:Eu, R Phosphors 

In parts A-E of this example all samplcs are activated 

a-SrAl,O,. This example demonstrates that brightness in 

these phosphors can be improved by 40-100% by charge 

compensation. In each case, B,03 is optionally added as a 

20 flux and can be substituted by an equivalent amount of boric 

acid. 0-phase material can be prepared for each of these 

exemplified materials using processing as in Example 1. 

A Substitution of Mg2+ for AI3+ in MAI,O,:Eu, R 

To make test sample SAO-ED-02Mg 

25 (SrAI,04:0.01Eu:0.02Dy with 0.02 Mg2+ (about 2 mol %) 

substituted for AI3+, phosphor components are combined in 

the following molar proportions: 

0.97 SrC0,+0.99 A1,0,+0.005 Eu,O,+O.Ol Dy,0,+0.02 MgOt 

0.1 B,O, 30 

Reference sample: SAO-ED-A (SrAI,04:0.01Eu:0.02Dy) 

without Mg was prepared by combining components in the 

following molar proportions: 

3s 0.97 SrCO,+A1,0,+0.005 Eu,O,+O.Ol Dy,O,+O.l B,O, 

Samples were prepared following the procedures of 

Example 2 to make a-phase phosphor. 

FIG. 3 illustrates the luminescence spectra of 

4o SrAI,O,:O.Ol Eu2+:0.02Dy3+ without (a) and with (b) Mg2+ 

(0.02) doping at room temperature 10 sec after exposure to 

a 13 W fluorescence lamp. FIG. 4 is a graph of decay curves 

of the after-glow of SrAI,0,:0.01EU2+:0.02Dy3+ with (a) 

and without (b) Mg2+ (0.02) doping in the first 60 minutes 

45 after exposed to a 13W fluorescence lamp. FIG. 5 illustrates 

the excitation spectra of the samples with (a) and without (b) 

Mg2+ codoping, monitoring the emission at 490 nm. The 

brightness (intensity of luminescence) is increased by 40% 

in the sample doped with Mg2+, which is believed to act as 

a charge compensator. 

The general recipe for preparation of MAI,O,:Eu, R 

phosphors containing Mg or Zn is: 

(l-2w-2y)MC0,+(1-q)Al~03+xEu~03+yR~03+2q MgO (or ZnO)+ 

zB203 

55 

where: 

~=0.0001 to 0.05; 

y=x to 2x; 

z=o to 0.10; 

q=O to 2y and is preferably equal to y; 

M is an alkaline earth metal, preferably Sr or a mixture of 

Sr with Ca, Ba, or with Ca and Ba; and 

R is one or more trivalent metal ions selected from the 

group Pr3+, Ho3+, Nd3+, Dy3+, Er3+, La3+, Lu3+, Ce3+, 

Y3+, Sm3+, Gd3+, Tb3+, Tm3+, and Yb3+ and trivalent 

Bi3+. 

60 

65 
US 6,267,911 B3 

15 

B: Substitution of Mg2+ for AI3+ in MAI,O,:Eu, Dy 

This example is used to show the improvement of phosphorescence by adding Mg (equal to the amount of Dy 

doped into the matrix) into phosphor samples which are 

doped with varying amounts of trivalent Dy. The samples 

were prepared in accordance to the following recipes: 

Sample 1: (SrAI,04,0.02Eu, 0.04 Dy) with 0.04 Mg (SAOED-04Mg) and without Mg (SAO-ED-B) 

SAO-ED-04Mg: 

0.94 SrC0,+0.98 A1,0,+0.01 Eu,0,+0.02 Dy,0,+0.04 MgO+ 

0.05 B,O, 

Reference: SAO-ED-B: 

0.94 SrC0,+1.00 A1,0,+0.01 Eu,0,+0.02 Dy,0,+0.05 B,O, 

Sample 2: (SrAI,04,0.02Eu, 0.08 Dy) with 0.08 Mg (SAOED-08Mg) and without Mg (SAO-ED-C) 

SAO-ED-08 Mg: 

0.90 SrC0,+0.96 A1,0,+0.01 Eu,0,+0.04 Dy,0,+0.08 MgO+ 

0.05 B,O, 

Reference: SAO-ED-C: 

0.90 SrC0,+1.00 A1,0,+0.01 Eu,0,+0.04 Dy,0,+0.05 B,O, 

Sample 3: (SrAI,04,0.02Eu, 0.12 Dy) with 0.12 Mg (SAOED-12Mg) and without Mg (SAO-ED-D) 

SAO-ED-12 Mg: 

0.84 SrC0,+0.94 A1,0,+0.02 Eu,0,+0.06 Dy,0,+0.12 MgO+ 

0.05 B,O, 

Reference: SAO-ED-D: 

0.84 SrC0,+1.00 A1,0,+0.02 Eu,0,+0.06 Dy,0,+0.05 B,O, 

and treated following the procedure of example 2. The 

improvements in the phosphors are described by the ratio of 

the after-glow between each sample and the corresponding 

reference sample at specified times following exposure to a 

4 W UV lamp. The results are in Table 2. It can be seen from 

the data of Table 2 that charge compensation tlrough codoping divalent ions (Mg or Zn) can greatly improve phosphor 

brightness. This is particularly true for phosphors in which 

a higher concentration of R3+ (e.g., Dy3+ or Dy3+, in 

combination with Y3+) is used. In general, co-doping of 

Mn2+/Zn '+ for AI3- or co-doping of Na+/K+ (or other 

monovalent alkali metal ions) for M2+ becomes more important in the phosphors which are heavily doped with R3+. 

TABLE 2 

Improvement of luminescence by adding MgZf as a charge compensator 

into SrAl,O,:Eu, Dv samples 

SAO-ED- SAO-EDafter 02 Mg/ 04 Mg/ SAO-ED-08 Mg/ SAO-ED-12 Mg/ 

min ref ref ref ref 

1 1.43 1.49 1.55 1.82 

10 1.45 1.45 1.44 1.39 

30 1.33 1.40 1.47 1.18 

60 1.21 1.20 1.00 1.11 

C: Substitution of Zn2+ for AI3+ in MAI,O,:Eu, R 

This example shows the improvement of phosphorescence by doping Zn2+ into the phosphor as a charge compensator. 

5 

10 

15 

20 

25 

30 

3s 

40 

4s 

so 

55 

60 

65 

16 

Samples were prepared by combining components in the 

following molar proportions: 

Sample: (SrAI,O4:0.02Eu, 0.04Dy) 

SAO-ED-04Zn with 0.04 ZnO 

0.94 SrC0,+0.98 A1,0,+0.01 Eu,O,+O.O2 Dy,0,+0.04 ZnO 

+0.05 B,O, 

Reference: SAO-ED-E without ZnO 

0.94 SrC0,+1.00 A1,0,+0.01 Eu,O,+O.O2 Dy,0,+0.05 B,O, 

The samples were then prepared following the procedure of 

Example 2. 

FIG. 6 illustrates luminescence spectra of 

SrA1,04:0.02Eu:0.04Dy with (a) and without (b) Zn2+ 

(0.04) codoping 10 second after exposed to a 13 W fluorescence lamp. FIG. 7 is a graph of the decay curves of the 

after-glow of SrAI,0,:0.02EU2+:0.04Dy3+ with (a) and 

without (b) Zn2+ (0.04) codoping in the first 60 minutes after 

exposed to a 13 W fluorescence lamp. Brightness is 

improved by up to 35% after codoping Zn2+ into the 

phosphor. 

D: Substitution of Na' for Sr2+ in MAI,O,:Eu, Dy 

This example demonstrates that monovalent sodium is 

effective in improving the phosphorescent intensity and 

persistence by acting as a charge compensator. 

Samples are prepared by combining components in the 

following molar proportions: 

SrA1,04:0.02EUZf, 0.04Dy3' 

with Na: SAO-ED-02Na 

0.90 SrCO,+A1,0,+0.01 Eu,O,+O.O2 Dy,0,+0.02 Na,CO,+O.l 

B2°3 

Reference sample without Na: SAO-ED 

0.94 SrCO,+A1,0,+0.01 Eu,O,+O.O2 Dy,O,+O.l B,O, 

and following the procedures of Example 2. 

FIG. 8 illustrates the spectra of the after-glow of the 

sample SrAI,04:0.02Eu:0.04Dy with (a) and without (b) 

Na' (0.04) codoping, 10 second after exposed to a 4 W UV 

lamp. FIG. 9 is a graph of decay curves of the after-glow of 

the samples (a) with and (b) without Na+ (0.04) codoping. 

The horizontal dashed line is the threshold of eye-sensitivity. 

FIG. 10 illustrates the excitation spectrum of 

SrAI,0,:0.02Eu2+:0.04Dy3+,0.04Na+, monitoring the emission at 520 nm. 

E: Co-Doping with Dy3+ and Y3+ 

This example is use to show the influence of trivalent 

yttrium ions on phosphorescence of the phosphor 

SrAl,O,:Eu,Dy. 

Samples are prepared by combining components in the 

following molar proportions: 

SrAl,04:0.02EuZf, 0.04Dy3+ 

with Y3+ SAO-ED-xY (SAO-ED-O.OlY, SAO-ED-O.O2Y, 

and SAO-ED-0.03Y) 

(0.94-2x) SrCO,+A1,0,+0.01 Eu,0,+0.02 Dy,O,+x Y,O,+O.l 

B2°3 

with x=O.Ol, 0.02 and 0.03; 

without Y3+: SAO-ED 

0.94 SrCO,+A1,0,+0.01 Eu,O,+O.O2 Dy,O,+O.l B,O, 

and treated as indicated in Example 2. 
US 6,267,911 B1 

17 18 

The results are shown in Table 3. It can be seen from the (l-2w-2y)SrC0,+Al,0,+xEu~03+y Dy,O,+zB,O, (optional) 

data of Table 3 that co-doping of Y3+, can significantly 

improve the brightneess and persistence of the phosphors. 

The doping level of Y3+, can be several times higher than 

and following the general procedure above to form single 

SrAI,04:0.02 Eu2+, 0.04Dy3+ single crystals were formed 

by combining the following components: 0.94SrC03+ that of Dy3+. 5 

AI,03+0.01Eu,03+0.02Dy,0, 

The mixture was processed by the laser heated pedestal 

growth method as described above. The after-glow spectrum 

of the single crystal, after exposure to a 4 W UV lamp for 

2 min, shows a broad band peaking at 520 nm with a 

characteristics of the phosphorescence of the crystal (a) after 

1 100 133 112 246 exposure to a 13 W fluorescent lamp. The decay curve of a 

commercial green phosphor ZnS:Cu (b) is also shown. The 

60 100 154 123 279 persistence time of the phosphorescence of the crystal is 

longer than 16 hours. 

Samples mixed with 0.05 B,03 (z=0.05) were also prepared and exhibited similar phosphor properties. 

B: Single crystals of SrAI,04:Eu2+, Dy3+ with AI3+ substituted by Mg2+ or Zn2+ 

In general, Sr&lz(l.q)0.2q XO:2xEu2+, 2y Dy3+ 

particularly Mg2+ or Zn", are prepared by combining 

TABLE 3 

The influence of trivalent yltrium on the phosphorescence of 

SrA1,0,:0.01Eu:0.02 Dv 10 

After SAO- 

(min) ED ref. SAO.ED.0.02 y SAO.ED.O.O1 y SAO.ED.0.03 y 

bandwidth of 80 nm. FIG. 11 is a graph of the decay 

10 100 139 124 264 

30 100 133 121 262 15 

Example 5 

Preparation of Single Crystal Phosphors of General Formula 20 

MAI,O,:EU~', R3+ 

Crystals of alkaline earth aluminates can be grown 

ski (1918) Z. Phys. Chem. 92:219) the floating zone method 

(W. G. Pfann (1952) Trans. AIME 194:747) or the laser 2s components as follOws: 

directly from a melt by the Czockraski method (J, Czochral- phosphors, where k=1-2x-2y and is a ion, 

heated pedestal growth method (B. M Tissue et al. (1991) J. 

Crystal Growth 109:323 and W. M. Yen (1995) "Preparation 

(l-2w-2y)SrC03+(1-q) Al,O,+xEu,O,+y Dy,0,+2q XO+zB,O, 

(optional) 

of single crystal fibers," in Insulating Materials for 

Singapore, Chapter 2. p.77. The exemplified crystals were 30 crysta1s. 

grown using the laser heated pedestal growth method. The 

following general method was employed in all cases: 

The phosphor components are mixed in molar proportions 

Optoelectronics, (F, Agullo-Lopez, ed,) World Scientific, and the genera' procedure above to form sing1e 

Sing1e crysta1s Of srAIz04:0.02 EU2+2 0.04Dy3+ with 

Mg2+ substituted for AI3+ were formed by combining the 

components: 

as desired to achieve a given phosphor. The addition of flux 0.94SrC03+0.98 A1,0,+0.01 Eu,0,+0.02Dy,0,+0.04MgO 

in the synthesis of single crystal phosphors is optional. 

The mixed phosphor components are milled or ground The mixture was Processed by the laser heated Pedestal 

into a homogeneous fine powder. The powder is then pressed growth method as described above. The after-glow spectrum 

into pellets under 1.3 ton/cm2 pressure. Pellets are prefired of the single crystal, after exposure to a 4 w Lwv lamp for 

at about 600" C. in air for about one hour. The prefired 2 min, shows a broad band Peaking at 520 nm with a 

material is pulverized and milled into a fine powder and the 40 bandwidth of 80 nm. FIG. 12 is a graph of the decay 

powder is again pressed into pellets, ne pellets are then characteristics of the phosphorescence of the crystal (a) after 

sintered at about 1300" C. for one hour in a flowing H,-N, exposure to a 13 w fluorescent lamp. 

gas flow having 2-5% (by volume) H, using a flow rate of Samples in which ZnO replaced MgO were also Prepared 

about 0.1 literimin. The gas flow is required to ensure that which exhibited similar PhosPhorescent Properties. 

the Eu ions are reduced to the divalent state, while other ions 45 c: Single crystals of SrA1204:Eu2', DY3+ with Sr2' substiin the mixture remain in their original valence state. The tuted by Na' Or 

sintered pellets are cooled down to room temperature at a In general Sr~A1204~rZ20~2XEU2'EU2'~ 2Y DY3+ 

rate of about 100" C. to about 500" C. per hour. phosphors, where k=1-2x-2y-2r and Z is a monovalent metal 

Cooled sintered pellets are cut into thin bars of cross- ion, Particularly Na' Or K+, are Prepared by combining 

section 1 mmxl mm. The bars are carefully cleaned using a SO components as fOllOWS: 

solvent (such as an alcohol or acetone) before introduction 

The crystal growth chamber is filled with inert gas (alone 

or mixed with el% H,) at a pressure of 1 atm. during the 

entire period of heating, melting and growing of crystals. ss crystals. 

The atmosphere used in the following specific examples was 

99.99% N,, The atmosphere of the growth chamber is 

selected so that europium is maintained in the 2+ valence 

state. 

The pulling speed of crystal growth employed was in the 60 

range of about 1 to about 5 mmimin. 

It is believed that a-phase material is obtained through 

this procedure. 

A. Green Phosphorescent Single Crystals of SrAI,04:Eu2+, 

Dy3+ 

In general SrAI,04:Eu2+, Dy3+ phosphors are prepared by 

combining components as follows: 

35 

(1-2w-2y-2r)SrCO3+A1,O3+x Eu,O,+y Dy,O,+r Z,O,+z B,O, 

into the growth chamber. (optional) 

and following the general Procedure above to form single 

Single crystals of SrA1204:0.02 EU2+, 0.04DY3+ with Na' 

substituted for Sr2+ were formed by combining the following components: 

0.90 SrCO,+A1,0,+0.01 Eu,O,+O.O2 Dy,0,+0.02 Na,CO, 

The mixture was processed by the laser heated pedestal 

growth method as described above. The after-glow spectrum 

of the single crystal, after exposure to a 4 W UV lamp for 

2 min, shows a broad band peaking at 520 nm with a 

65 bandwidth of 80 nm. FIG. 13 is a graph of the decay 

characteristics of the phosphorescence of the crystal (a) after 

exposure to a 13 W fluorescent lamp. 
US 6,267,911 B3 

19 

Single crystal phosphors with similar properties can be 

prepared by replacing Na,CO, with QCO,. 

D: Single crystal fibers of CaAl,0,:Eu2+, Nd3+ 

In general CaAl,0,:Eu2+, Nd3+ phosphors are prepared 

by combining components as follows: 

(l+t) CaCO,+Al,O,+x Eu,O,+y Dy,O,+z B,O, (optional) 

where t represents an excess amount of CaCO, added to 

ensure obtaining the CaAl,O, phase. No excess CaCO, 

needs to be added when preparing single crystals by the laser 

heated pedestal or floating zone methods. The mixture is 

processed by the general procedure above to form single 

crystals. 

Phosphorescent purple single crystal fibers of 

CaAl,O,:O.Ol Eu2+, 0.01 Nd3+ were prepared by combining 

components in the following molar proportions: 

1.05 CaCO, (excess)+A1,0,+0.005 Eu,0,+0.005 Nd,O, 

and following the procedures described above. 

The after-glow spectrum of the single crystal, after exposure to a 4 W UV lamp for 2 min, shows a broad band 

peaking at 444 nm with a bandwidth of 50 nm. FIG. 14 is a 

graph of the decay characteristics of the phosphorescence of 

the crystal (a) after exposure to a 13 W fluorescent lamp. The 

persistence time of the phosphorescence of the crustal is 

longer than 16 hours. 

Single crystals of CaAl,0,:Eu2+, Nd3+ with Mg2+ 

(substituted for AI3+ in the matrix were also synthesized and 

they exhibited similar phosphorescent properties. 

E: Mixed-single -crystal fibers of Sr,.,Ba,Al,0,:Eu2+, Dy3+ 

Single crystal fibers of Sro,,,Bao,,,Al,0,:0.01Eu2+, 0.01 

Dy3+ were prepared by combining the following components: 

0.49 SrCo,+0.49 BaCO,+A1,0,+0.005 Eu,O,+O.OOS Dy,0,+0.05 

B,O,(optional) 

and following the procedures above. The phosphorescent 

spectrum of the crystals shows a broad peak at 520 nm, 

similar to that of SrAl,0,:Eu2+, Dy3+ phosphors. FIG. 15 is 

a graph of the decay characteristics of the mixed single 

crystal (a) after exposure to a 13 W fluorescent lamp. The 

mixed crystal shows very weak phosphorescence compared 

to SrAl,0,:Eu2+, Dy3+. 

Those of ordinary skill in the art will appreciate that the 

phosphors of this invention can be prepared using starting 

materials other than those specifically disclosed herein and 

that procedures and techniques functionally equivalent to 

those described herein can be employed to make and assess 

the phosphors herein. Those of ordinary skill in the art will 

also appreciate that the host matrix of this invention may 

accommodate metal ions other than those specifically mentioned herein without significant effect upon phosphor properties. 

All references cited herein are incorporated by reference 

herein to the extent that they are not inconsistent herewith. 

We claim: 

1. A phosphor represented by the formula: 

M,p.1,0,:2xEUZf, ZyR3' 

wherein k=1-2x-2y, x is a number ranging from about 

0.0001 to about 0.05, y is a number ranging from about 

0.0001 to about 0.15, M is an alkaline earth metal, and R3+ 

is one or more trivalent metal ions and wherein a portion of 

the AI3+ in the host is substituted by a divalent ion. 

20 

2. The phosphor of claim 1 wherein M is Sr. 

3. The phosphor of claim 1 wherein x is a number ranging 

from about 0.005 to about 0.02. 

4. The phosphor of claim 1 wherein the value of y is two 

s times the value of x. 

5. The phosphor of claim 1 wherein R3+ is selected from 

the group Pr3+, Ho3+, Nd3+, Dy3+, Er3+, La3+, Lu3+, Ce3+, 

Y3+, Sm3+, Gd3+, Tb3+, Tm3+, Yb3+ and Bi3+. 

6. The phosphor of claim 1 wherein R3+ is Dy3+. 

7. The phosphor of claim 1 wherein the divalent ion is 

Mg2+ or Zn2+ or a mixture thereof. 

8. The phosphor of claim 7 wherein the divalent ion is 

present in the phosphor in an amount about equal to the 

amount of R3+ trivalent metal ion doped into the phosphor. 

9. The phosphor of claim 1 which is prepared employing 

flux. 

10. The phosphor of claim 9 wherein the flux is B,O, or 

equivalents thereof. 

11. The phosphor of claim 1 represented by the formula: 

io 

IS 

20 

M@.l,~,0,.qXO:2xEuZf, ZyR3' 

where X is a divalent ion and q is the amount of divalent ion 

substituted for AI3+ in the phosphor and q is a number 

12. The phosphor of claim 1 wherein M is selected from 

the group Sr, a mixture of Sr with Ca, a mixture of Sr with 

Ba or a mixture of Sr, Ca and Ba. 

13. The phosphor of claim 1 wherein a portion of the M2+ 

3o in the phosphor is substituted with a monovalent metal ion. 

14. The phosphor of claim 13 wherein the monovalent 

metal ion is Na+ or K+. 

15. The phosphor of claim 13 wherein the monovalent 

metal ion is present in an amount about equal to the amount 

16. The phosphor of claim 1 which is formed as a single 

17. The phosphor of claim 16 which has the formula: 

25 ranging from about equal to 0.001 to about equal to 0.45. 

35 of R+, trivalent metal ion in the phosphor. 

crystal. 

Sr,,,A1,,,0.0.04Mg0:0.02Eu~+,0.04Dy3+ 

40 

18. A phosphor represented by the formula: 

M,p.l,0,:2wE~~+, 2y1R,3+, ZyzY3' 

45 wherein k=1-2x-2y, y1+y2=y, x is a number ranting from 

about 0.0001 to about 0.05, y is a number ranging from 

about 0.0001 to about 0.15, M is an alkaline earth metal, and 

R13+ is one or more trivalent metal ions. 

19. The phosphor of claim 18 wherein M is Sr. 

20. The phosphor of claim 18 wherein R13+ is selected 

from the group Pr3+, Ho3+, Nd3+, Dy3+, Er3+, La3+, Lu3+, 

Ce3+, Sm3+, Gd3+, Tb3+, Tm3+, Yb3+ and Bi3+. 

21. The phosphor of claim 18 wherein R13+ is Dy3+. 

22. The phosphor of claim 18 wherein M is Sr. 

23. The phosphor of claim 18 wherein a portion of the 

M2+ in the phosphor is substituted with a monovalent metal 

ion. 

24. The phosphor of claim 23 wherein the monovalent 

metal ion is Na+ or K+. 

25. The phosphor of claim 18 wherein a portion of the 

AI3+ in the phosphor is substituted with a divalent ion. 

26. The phosphor of claim 25 wherein the divalent ion is 

Mg2+ or Zn2+. 

27. The phosphor of claim 18 wherein x is a number 

28. The phosphor of claim 18 wherein the value of y is 

so 

55 

60 

65 ranging from about 0.005 to about 0.02. 

two times the value of x. 
US 6,267,911 B3 

21 

29. The phosphor of claim 18 which forms as a single 

30. The phosphor represented by the formula: 

crystal. 

M,p.l,0,:2xEuZf, ZyR3’ 

wherein k=1-2x-2y, x is a number ranging from about 

0.0001 to about 0.05, y is a number ranging from about 

0.0001 to about 0.15, M is an alkaline earth metal, and R3+ 

is one or more trivalent metal ions and wherein a portion of 

M2+ in the phosphor is substituted by a monovalent metal 

ion. 

31. The phosphor of claim 30 in which the monovalent 

metal ion is Na+ or K+. 

32. The phosphor of claim 31 in which the monovalent 

metal ion is present in the phosphor in an amount about 

equal to the amount of R+3 , trivalent metal ion doped into 

the phosphor. 

33. The phosphor of claim 30 which can be represented by 

the formula: 

~,p.i,0,.r~,0:2w~u~+, 2y~3+ 

where Z is a monovalent ion and r can range from greater 

than 0 to about 0.30. 

34. The phosphor of claim 30 wherein R3+ is selected 

from the group Pr3+, Ho3+, Nd3+, Dy3+, Er3+, La3+, Lu3+, 

Ce3+, Y3+, Sm3+, Gd3+, Tb3+, Tm3+, Yb3+ and Bi3+. 

35. The phosphor of claim 30 wherein M is Sr. 

36. The phosphor of claim 30 wherein R3+ is Dy3+. 

37. The phosphor of claim 30 wherein x is a number 

38. The phosphor of claim 30 wherein the value of y is 

39. The phosphor represented by the formula: 

ranging from about 0.005 to about 0.02. 

two times the value of x. 

M,p.l,0,:2xEuZf, ZyR3’ 

wherein k=1-2x-2y, x is a number ranging from about 

0.0001 to about 0.05, y is a number ranging from about 

0.0001 to about 0.15, M is an alkaline earth metal, R3+ is one 

or more trivalent metal ions and which is formed as a single 

crystal. 

40. The phosphor of claim 39 wherein M is Sr. 

41. The phosphor of claim 39 wherein R3+ is Dy3+. 

22 

42. The phosphor of claim 39 which has the formula 

43. The phosphor of claim 39 wherein M is Ca and R3+ 

44. The phosphor of claim 39 wherein M is a mixture of 

45. Amethod for making a single crystal phosphor which 

Sr,,,4A1204:0.02Eu2+, 0.04Dy3+. 

is Dy3+. 

Sr and Ba. 

comprises the steps: 

s 

(a) combining phosphor components according to the 

stoichiometric amounts of the formula: 

wherein k=1-2x-2y, x is a number ranging from about 

0.0001 to about 0.05, y is a number ranging from about 

0.0001 to about 0.15, M is an alkaline earth metal and 

R3+ is one or more trivalent metal ions, to form a 

powder; 

(b) sintering the powder in a reducing atmosphere; 

(c) quenching the sintered material to a temperature below 

650” C. to obtain a phosphor material that substantially 

remains in the 0-phase at room temperature; and 

(d) crystalizing single crystals from the quenched sintered 

phosphor of step (c) under an inert atmosphere. 

46. Amethod for making a single crystal phosphor which 

(a) combining the phosphor components according to the 

comprises the steps of 

stoichiometry of the formula: 

~,p.i,0,:2w~u~+, 5~3+ 

where k=1-2x-2y, x is a number ranging from about 

0.0001 to about 0.05, y is a number ranging from about 

0.0001 to about 0.15, M is an alkaline earth metal and 

R3+ is one or more trivalent metal ions to form a 

powder; 

(b) sintering the powder in a reducing atmosphere; and 

(c) growing single crystals from the sintered powder 

47. The method of claim 46 wherein a flux is combined 

under an inert atmosphere. 

with phosphor components in step (a). 

*****