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# United States Patent (io) Patent 

## No.: 

# US 6,267,911 B1 Yen et al. (45) 

## Date 

## of Patent: *Jul.

## 31,2001

(54) 

### PHOSPHORSWITH 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



### ...................... 2521301.4R; 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)



### . 765925A1 211997 (EP)



### .

51031037 711976 (JP)



### . 5078659 311993 (JP)



### . 94029416 B2 411994 (JP)



### . 94029417B2 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 0.0001to 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

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## US 6,267,911 B1 Page 2

OTHER PUBLICATIONS Matsuzawa et al, “ANew 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), “ANew 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

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## US 

## 6,267,911B3 

## 1 PHOSPHORSWITH 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 Statesgovernment 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 inU.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-dopingDY+~ with EU2+ into SrAI,O, and Nd+3 withEu" 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 ofthe Sr2' ofthe 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, andxisanumber not equalto 0.The matrix comprises europium and a rare earth metal, manganese, tin or bismuth as co-activators.

JPPatent 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'. Inthe 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 inthe 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 ofEuropium 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 sitesinto alkaline earth metal ion sites (e.g., Sr2' sites)inthe 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 amountofmonovalention introduced into the phosphor is substantially equivalent to the molar amount of trivalent rare earth metal ion (e.g., Dy3+). It isbelieved 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 

## 6,267,911B3 

## 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-dopedphosphor to replace alkaline earth metal ion (e.g., Sr”) in the host. Co-doping with

### Y+3 ismore preferred. The amount of

### Y+3 that canbe introduced to replace the alkaline earthmetal ion isup to three times themolar amountofother 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 synthesisofthe alkaline earth aluminatephosphors resultsin phosphors with significantly improved properties. Thephosphors 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 tobe substantiallyinthe lower temperature phase (a-phase). Application of the quenching step in the synthesis of SrAI,O, matrix phosphors isbelieved 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 subjectedto quenching during synthesis, tophosphors 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.

Thisinvention alsoprovides 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 forAI3+ or in which Na+ or 

### K+ (or other alkali metal ions) are substituted for M2+ascharge 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 

### 15hours.

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 13W 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 forAI3+, (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 forAI3+.

FIG. 

### 6 illustrates luminescent spectra of SrAI,0,:0.02Eu2+, 0.04Dy3+ (b) and the corresponding phosphor with 4 mol % Zn2+substituted forAI3+, (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 forAI3+, 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 13W 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 13W 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 13W 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 13W 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’,0.01Dy3+ 60 after exposure to a 13W fluorescent lamp. 5

2o

25

3o 60 minutes after exposure to a 13Wfluorescent lamp.

40

45

DETAILED DESCRIPTION OF THE INVENTION This invention relates to long-persistence green phos65 phors. Several basic physical factors shouldbe consideredin 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 providethe desired color (dependent uponthe 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 inthe phosphors of this invention is Eu".

Persistent phosphorescence was discovered in the 11th century

### inChinaandJapan and

### inthe 16th century 

### inEurope (Shionoya, S.(1998) in

### PhosphorHandbook, Shionoya, S. and Yen,W. M. (eds.), CRC Press, Inc., Boca Raton, N.Y., p. 3).The phenomenon involves twokindsof active centers: Phosphors of this invention have the general formula:

where is 1-2x-2y; can rangefrom abouto.oool to about 0.05and ispreferably about 0.001to about 0.02; y canrange from about 0.0001to 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 manyaspects remain creatingpropertrappingcenters 

### inthe 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 VAmetal 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 creThemain differencebetweenthese threephenomena appears atingtrapping centers includetrivalent 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 showpersistent phospho- This invention demonstrates that energy efficiency, the rescence. Deeper trapping centers canbe 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 aportion ofN3+ 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 

### inwhich 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 ofthis invention canexhibit enhanced Rb'. These monovalent and divalent ions arebelieved 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 inpowintensity 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 ofthis 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 asindicated 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 apersistence time of20to 40minutes. 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 1300" 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 canbe replaced in all formulations of this invention materials, including single crystals and single crystal fibers, 60 by an amount of H3B03sufficient to provide an equivalent of this invention can exhibit phosphorescence persistence molar amount of B (i.e., 2H3B03replace each B,03). times of greater than about 

### 3-5 hrs. More preferred phos- This invention is based at least inpart on the finding that phors exhibit persistence times greaterthan 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 steptorapidly 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 

## 6,267,911B3 

## 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 aluminatesof this invention resultsin 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 aroom 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 quenchingis 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 orby 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 attemperature 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 lowertemperature a-phase.The crystal structureofthe high temperature phase, fl-SrAl,O,, ishexagonal.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 stepin 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 inwhich divalent and monovalent ions are substituted into the matrix.

Charge compensators can be included in either o(quenched)- and a(non-quenched)-SrAlz04to 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-dopingmonovalent alkalimetal 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 ispreferably about 0.005to about 0.02, y can range from about 0.0001to about 0.15and is preferably 20 equal to 2x. M is most generally an alkaline earth metal, but is preferably Sror a mixture of Srwith Ca, Ba or both. R is generally one or more trivalent metal ions, but ispreferably 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 aremilled 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 ifhigh 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 atthat temperature for afewminutes. This step minimizes thermal shockto 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 offormula 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, orR, may represent amixture ofdifferent trivalent metal ions. The number x can range from about 0.0001 to about 0.05and ispreferably about 0.005to 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 

## 6,267,911B3 

## 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 phosphorshave the general formula: M@.l,-,O,.qXO: 2wEuZf,2yR3', where k=1-2x-2y, x can range from about 0.0001 to about 0.05andispreferably about 0.005to about 0.02, y canrange from about 0.0001to 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 replaceAI3+, 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 andnon-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 canrange from about 0.0001to 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+,ispreferably 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 asindicated inthe 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) isoptional. The quenching step discussed above is also optional when making single crystals or single crystalfibers.

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 filledwith 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 theLHGPprocesswasatwined 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 centimetersinlength. 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 ensurethat the crystalwasCaAl,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 ispreferable to ensure formation ofthe 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.) forten 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 ofparagraph Awhichalso containup

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

### Zn" substituted forAI3+, 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 forp~3+ 

### inthe formulaorup 5 quenched from the sintering temperature to a temperature to about

# zY moles of amonovalent 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. Anoptionalintermediate 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 ofparagraph are those wherein R3+ 

### is Dy3+or quenched from the intermediate high temperature to a tema ofDy3+and y3+, phosphor materialofclaim 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+,

### inthe 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 

### 10wherein said phosphor further comprises up to about 2y phor materials of paragraph C include phosphors further 

### 1s high temperaturephase to a temperaturesubstantially to room temperature. The quenching step is preferably

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

### K+ D,Asingle crystalphosphor material containing a phosphor 20 sizedwith aquenching step are designated O-phase retained 

### in the high temperaturephase.

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 VAtrivalent 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 1.3ton/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 1.3ton/cm2pressure. The powder or the pressed pellets are sintered at about 1,300' C. for about one hour inaH,N, flowing gasmixture k is 1-2x-2y; x is a number ranging from about 0.0001 to about 0.05; (i.% a reducing atmosphere) containing2-5'32 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 componentstoproduce afine 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 Sror or combinations thereof, phors



### is a number 

### ranging from about to about 3x; and

group pr3+2 Ho3-2Nd3+2 Dy3+2 Er3+2La3'2 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 molesof

### 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 1hour at a temperature of about to the lower temperaturea-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 stepse or f at about 65 Green Phosphors
1300"C. for one hour in a reducing atmosphere;

## US 

## 6,267,911B3 

## 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 forAI3+ ascharge 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 ispreferably pressed into pellets under 1.3ton/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 1.3ton/cm2 pressure.

The powder or the pressed pellets are sintered at about 1,300' C. for about one to two hours in aH,N, flowing gas mixture containing 2-5% H, by volume at a flow rate of about 0.1liter per minute.The sampleisthen cooledto 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 Preparationof 0-Phase SrAl,O,:Eu, R where Ris aTrivalent Rare Earth Ion or Bi3+ and Comparison with anAnalogous 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 0.0001to about 0.05;

y=x to 2x;
z=oto 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 1to 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 wasdivided into two parts. Onepart (labeled asa-SAO-EDfor a-SrAl,O,) wasprocessed asindicated 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 asindicatedin Table 1.Table 1 provides after-glow intensity measurements of the 0-phase material relative to the a-phase material (the reference).

FIG. 

### 1illustratestheluminescent spectraof (a) fl-SrAI,O, phosphor (0-SAO-ED) and(b) a-SrAl,O, (a-SAO-ED) 10 sec. after exposure to a 13W fluorescent lamp. The luminescent spectrumofthe 0-phase issimilarto that of a-phase, but shifted to the long wavelength sideby about 3nm. 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 13W 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 13W 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 ofboric acid. 0-phase material can be prepared for each of these exemplified materials using processing as in Example 1. A Substitution of Mg2+forAI3+ 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 forAI3+, 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 10sec after exposure to a 13W fluorescence lamp. FIG. 

### 4is 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 13Wfluorescence lamp. FIG. 5 illustrates the excitation spectraofthe sampleswith (a) andwithout (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=oto 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 

## 6,267,911B3 

## 15 B: Substitution of Mg2+ forAI3+ in MAI,O,:Eu, Dy This example isused 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 describedby the ratio of the after-glow between each sample and the corresponding reference sample at specifiedtimes following exposure to a 4W UV lamp. The results areinTable2.It canbe seen from the data of Table2 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+ becomesmore important in the phosphors which are heavily doped with R3+.
TABLE 2 Improvement of luminescence by adding MgZfas a charge compensator into SrAl,O,:Eu, Dv samples
SAO-ED- SAO-EDafter 02 Mg/ 04 Mg/ SAO-ED-08Mg/ 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+ forAI3+ 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 Sampleswere prepared by combining components in the following molar proportions: Sample: (SrAI,O4:0.02Eu, 0.04Dy) SAO-ED-04Znwith 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 sampleswere 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 13W fluorescence lamp. FIG. 

### 7is 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) codopinginthe first 60minutes 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, 10second 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. Thehorizontal dashed lineisthe thresholdofeye-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 crystalswere 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 asdescribed 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 characteristicsofthe phosphorescence ofthe crystal (a) after 1 100 133 112 246 exposure to a 13W fluorescentlamp. 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 16hours.

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 SingleCrystal 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: directlyfrom a meltbythe Czockraski method 

### (J,Czochral- phosphors, wherek=1-2x-2y and is a ion,

heatedpedestal growth method 

### (B. MTissue et al. (1991)J. Crystal Growth 109:323andW. 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 componentsare 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+0.98A1,0,+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 ahomogeneous finepowder. The powderisthen pressed growth method asdescribed above.The after-glow spectrum into pellets under 1.3ton/cm2 pressure. Pellets are prefired ofthe single crystal, after exposure to a 4

## w Lwvlamp 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 ispulverized and milled into afine 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 characteristicsofthe phosphorescence ofthe 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 Samplesin 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 otherions 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 amonovalent metal

Cooled sintered pellets are cut into thin bars of cross- ion, Particularly Na' Or 

### K+, are Prepared by combining section 1mmxl mm. The bars are carefully cleaned using a SO components as fOllOWS: solvent (such as an alcohol or acetone) before introduction

The crystalgrowth chamber isfilled with inert gas (alone or mixed with el% H,) at a pressure of 1atm. during the entire period of heating, melting and growing of crystals. 

### ss crystals. The atmosphere used in the following specificexampleswas 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 1to 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

Singlecrystals ofSrA1204:0.02 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 asdescribed 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 characteristicsofthe phosphorescence ofthe crystal (a) after exposure to a 13W fluorescent lamp.

## US 

## 6,267,911B3 

## 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, needstobe addedwhen 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+,0.01Nd3+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 50nm. FIG. 

### 14is a graph ofthe decay characteristicsofthe phosphorescence of the crystal(a) afterexposureto a 13Wfluorescent lamp. The persistence time of the phosphorescence of the crustal is longer than 16hours.

Single crystals of CaAl,0,:Eu2+, Nd3+ with Mg2+ (substituted forAI3+ in the matrix were also synthesized and they exhibited similar phosphorescent properties. E: Mixed-single -crystalfibersofSr,.,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. 

### 15is a graph of the decay characteristics of the mixed single crystal (a) after exposure to a 13W fluorescent lamp. The mixed crystal showsvery weakphosphorescence 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 effectupon 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 0.0001to about 0.15, M is an alkaline earth metal, and 

### R3+ is one or more trivalent metal ions and wherein aportion of theAI3+ 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 

### 1wherein x is anumber ranging from about 0.005 to about 0.02.



### 4.The phosphor of claim 

### 1wherein the value of y is two 

### s times the value of x. 5.The phosphor of claim 

### 1wherein 

### 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 

### 1which is prepared employing flux.



### 10.The phosphor of claim 

### 9 wherein the flux is B,O, or equivalents thereof.



### 11.The phosphor of claim 

### 1represented by the formula: 

### io

IS

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

### X is a divalent ion and q is the amount of divalention substituted for AI3+in the phosphor and q is a number



### 12.The phosphor of claim 

### 1wherein 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 

### 1wherein 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 ispresent in an amount about equal to the amount



### 16.The phosphor of claim 

### 1which is formed as a single


### 17.The phosphor of claim 

### 16 which has the formula: 25 ranging from about equal to 0.001to 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 0.0001to 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 

## 6,267,911B3 

## 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 0.0001to about 0.15, 

### M is an alkaline earth metal, and 

### R3+ is one or more trivalent metal ions and wherein aportion 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 ofclaim

### 30which canbe 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 0.0001to about 0.15,

### M is an alkaline earth metal,

### R3+isone or more trivalent metal ions andwhich 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 0.0001to about 0.05, y is anumber ranging from about 0.0001to 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) quenchingthe sintered materialto a temperature below

650” C.to obtain a phosphor material that substantially remains in the 0-phase at room temperature; and (d) crystalizing single crystalsfrom 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 0.0001to about 0.05, y is anumber ranging from about 0.0001to 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). 

## *****