Abstract:
The application relates to fluorescent powder which has a garnet structure and can be effectively excited by ultraviolet light or blue light, a method for preparing the fluorescent powder, and a light emitting device, an image display device and an illumination device comprising the fluorescent powder. A chemical formula of the fluorescent powder is expressed as: (M 1 a-xM 2 x)ZrbM 3 cOd, where M 1  is one or two elements selected from Sr, Ca, La, Y, Lu and Gd, Ca or Sr being necessary; M 2  is one or two elements selected from Ce, Pr, Sm, Eu, Tb and Dy, Ce being necessary; M 3  is at least one element selected from Ga, Si, and Ge, Ga being necessary; and 2.8≦a≦3.2, 1.9≦b≦2.1, 2.8≦c≦3.2, 11.8≦d≦12.2, and 0.002≦x≦0.6.

Description:
CROSS-REFERENCE TO RELATED PATENT APPLICATIONS 
       [0001]    This patent application is a United States national phase patent application based on PCT/CN2015/085962 filed Aug. 3, 2015, which claims the benefit of Chinese Patent Application No. 201410546588.0 filed Oct. 15, 2014, the disclosures of which are hereby incorporated herein by reference in their entirety. 
     
    
     TECHNICAL FIELD 
       [0002]    The application relates to the field of inorganic Light Emitting Diode (LED) luminous materials, particularly to a fluorescent powder, and more particularly to a fluorescent powder having a garnet structure. The fluorescent powder is effectively excitable by ultraviolet light or blue light to emit visible light. The application also relates to a method for preparing the fluorescent powder, and a light emitting device, an image display device and an illumination device comprising the fluorescent powder. 
       BACKGROUND 
       [0003]    An LED has the advantages of high light emitting efficiency, low power consumption, long life, low pollution, small size, high operation reaction speed and the like, and is widely applied to the fields of illumination, display and the like, wherein YAG:Ce 3+  (Y 3 Al 5 O 12 :Ce 3+ ) yellow powder matches a blue-light LED chip to achieve white light, has the characteristics of high efficiency, low cost, simple manufacture and the like, and is thus widely adopted. An important reason lies in YAG yellow powder having a garnet structure has extremely stable physical and chemical properties and incomparable high light efficiency. Thus, the research and development of fluorescent powder having a garnet structure will always be the research hot focus at home and abroad. Particularly, a Ce 3+  ion having a d-f transition serves as an activating agent, and an excitation spectrum presented thereby in the garnet structure has very strong excitation peaks in an ultraviolet area and a blue-light area separately, and can well match ultraviolet, near-ultraviolet or blue-light chips. 
         [0004]    The synthetic temperature of a garnet structure compound such as YAG (and YAG doped with Ga, La, Lu, Gd and other elements) and Ca 3 Sc 2 Si 3 O 12  is usually more than 1,500° C. Reduction of the synthetic temperature can reduce the cost, and the effects of energy conservation and emission reduction are obvious. Therefore, searching for garnet-type fluorescent powder capable of being synthesized at a low temperature plays an important role in promoting energy conservation and emission reduction and improving the level of ecological civilization. 
         [0005]    The general formula of the garnet structure is A 3 B 2 (XO 4 ) 3 , where A, B and X usually refer to octa-coordination, hexa-coordination, and tetra-coordination; and B and an adjacent atom O form an octahedron usually, and X and the adjacent atom O form a tetrahedron usually. B-site elements of a garnet structure compound doped with rare-earth elements and taken as fluorescent powder are classified, and there are divalent metal elements (such as a non-patent document 1, Mg in Lu 2 CaMg 2 (Si,Ge) 3 O 12 ), trivalent metal elements (such as the patent document 1, Al in YAG; a patent document 2, Sc in Ca 3 Sc 2 Si 3 O 12 ), and pentavalent metal elements (such as a patent document 3, Ta in Li 5 La 2 Ta 2 O 12 ), usually; and the B-site elements are compounds Ca 2 LaZr 2 Ga 3 O 12  of a tetravalent metal element Zr (such as the non-patent document 2), and solid solution of rare-earth elements as fluorescent powder is not reported yet. In addition, on the basis of this series of garnet structure compounds, Ga is partially replaced with tetravalent metal elements, such that the usage of Ga and the usage of lanthanide elements may be reduced to obtain new compounds such as Ca 3 Zr 2 Ga 2 SiO 12 , Ca 3 Zr 2 Ga 2 GeO 12  and the like, and the synthetic temperatures of this series of compounds and the new compounds obtained by doping with the rare-earth elements are within 1,400° C. 
         [0006]    In the conventional, a minority of Zr-comprising garnet structure compounds exists. According to crystallography sites occupied by Zr, these compounds are mainly divided into three classes:
       the first class is representative of Ca 3 Sc 2 Si 3 O 12  in a patent document 3, wherein Zr serving as a small number of doped elements partially replaces Si, Ge and other elements located in the site X;   the second class is that Zr occupies the site B, for example, Ca—Zr in patent documents 4 and 5 replace (Y/La/Lu) and Al in (Y/La/Lu) 3 Al 5 O 12  respectively, and Zr—Mg replace Al—Al in (Y/La/Lu) 3 Al 5 O 12 ; and   the third class is that a small number of Zr serving as a charge compensating agent occupies the site A, and for example, in a patent document 6, Zr 4+  or Hf 4+  is adopted to serve as a charge compensating agent replaced with a small number of elements.       Non-patent document 1: Anant A. Setlur, William J. Heward, Yan Gao, Alok M. Srivastava, R. Gopi Chandran, and Madras V. Shankar, Chem. Mater., 2006, 18(14):3314-3322;   Non-patent document 2: S. Geller, Materials Research Bulletin, 1972, 7(11):1219-1224;   Patent document 1: U.S. Pat. No. 5,998,925B;   Patent document 2: U.S. Pat. No. 7,189,340B;   Patent document 3: CN 103509555 A;   Patent document 4: CN 103703102 A;   Patent document 5: CN 101760197 A; and   Patent document 6: CN 101323784 A.   
 
       SUMMARY 
       [0018]    The application is intended to provide a fluorescent powder which can be effectively excited by ultraviolet light or blue light to emit light, a preparation method therefor, and a light emitting device, an image display device and an illumination device comprising the fluorescent powder. 
         [0019]    To this end, the application adopts the technical solution as follows. 
         [0020]    The application provides a fluorescent powder and the fluorescent powder has a garnet crystal structure. A chemical formula thereof is expressed as: (M 1   a-x M 2   x )Zr b M 3   c O d , wherein M 1  is one or two elements selected from Sr, Ca, La, Y, Lu and Gd, Ca or Sr being necessary; M 2  is one or two elements selected from Ce, Pr, Sm, Eu, Tb and Dy, Ce being necessary; and M 3  is at least one element selected from Ga, Si, and Ge, Ga being necessary. 2.8≦a≦3.2, 1.9≦b≦2.1, 2.8≦c≦3.2, 11.8≦d≦12.2, and 0.002≦x≦0.6. Furthermore, 2.9≦a≦3.1, 1.9≦b≦2.0, 2.9≦c≦3.1, 11.9≦d≦12.1, and 0.02≦x≦0.4, preferably. Furthermore, a=3.0, b=2.0, c=3.0, and d=12.0, preferably. 
         [0021]    The garnet structure refers to a crystal structure which belongs to a cubic system and has an Ia-3d space group, the general formula thereof is A 3 B 2 (XO 4 ) 3 , where A, B and X usually refer to octa-coordination, hexa-coordination, and tetra-coordination; and B and an adjacent atom O form an octahedron usually, and X and the adjacent atom O form a tetrahedron usually. In the fluorescent powder, M 1  and M 2  occupy the site A, Zr occupies the site B of the hexa-coordination, M 3  occupies the site X, and it may be proved by refinement of an X-powder ray diffraction pattern (it is illustrated with refinement of an X-powder ray diffraction pattern of (Ca 2 Y 0.94 ,Ce 0.06 )Zr 2 Ga 3 O 12 , the refinement range is 10°≦2θ≦100°, a target material used by a diffractometer is a Co target, λ=0.178892 nm, and an initial model adopted for refinement is a typical garnet structure compound Y 3 Al 5 O 12 ; a refinement result is that a crystal system, a space group, crystal cell parameters and refinement residual factors are shown in Table 1; structural information such as atom coordinates, site occupancy ratios and temperature factors are shown in Table 2; a data fitting chart is shown in  FIG. 7 ). 
         [0000]    
       
         
               
             
               
               
               
             
               
             
               
               
               
             
               
             
               
               
               
             
           
               
                 TABLE 1 
               
               
                   
               
               
                 Crystal system, space group, crystal cell parameters and 
               
               
                 refinement residual factors of (Ca 2 Y 0.94 ,Ce 0.06 )Zr 2 Ga 3 O 12   
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                   
                 Molecular formula 
                 (Ca 2 Y 0.94 ,Ce 0.06 )Zr 2 Ga 3 O 12   
               
               
                   
                 Crystal system 
                 Cubic system 
               
               
                   
                 Space group 
                 Ia-3d 
               
             
          
           
               
                 Crystal cell parameters: 
               
             
          
           
               
                   
                 a = b = c (Å) 
                 12.6316(3) 
               
               
                   
                 α = β = γ (deg) 
                 90 
               
               
                   
                 V (Å 3 ) 
                 2015.48(0) 
               
               
                   
                 Z 
                 8 
               
             
          
           
               
                 Residual factors: 
               
             
          
           
               
                   
                 R p  (%) 
                 8.32 
               
               
                   
                 R wp  (%) 
                 11.6 
               
               
                   
                 x 2   
                 3.18 
               
               
                   
                   
               
             
          
         
       
     
         [0000]    
       
         
               
             
               
               
               
               
             
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
             
           
               
                 TABLE 2 
               
             
             
               
                   
               
               
                 Structural information such as atom coordinates, site occupancy 
               
               
                 ratios and temperature factors of (Ca 2 Y 0.94 , Ce 0.06 )Zr 2 Ga 3 O 12   
               
             
          
           
               
                   
                   
                 Site 
                   
               
               
                   
                 Atom position 
                 occupancy 
                 Temperature 
               
             
          
           
               
                 Atom 
                 Site 
                 x 
                 y 
                 z 
                 ratio 
                 factor 
               
               
                   
               
             
          
           
               
                 Ca 
                 24c 
                 0.12500 
                 0.00000 
                 0.25000 
                 0.16667 
                 0.16903 
               
               
                 Ce 
                 24 
                 0.12500 
                 0.00000 
                 0.25000 
                 0.00500 
                 0.16903 
               
               
                 Y 
                 24c 
                 0.12500 
                 0.00000 
                 0.25000 
                 0.07833 
                 0.16903 
               
               
                 Zr 
                 16a 
                 0.00000 
                 0.00000 
                 0.00000 
                 0.16667 
                 0.01778 
               
               
                 Ga 
                 24d 
                 0.37500 
                 0.00000 
                 0.25000 
                 0.25000 
                 0.13025 
               
               
                 O 
                 96h 
                 0.97016 
                 0.05468 
                 0.15353 
                 1.00000 
                 0.11939 
               
               
                   
               
             
          
         
       
     
         [0022]    In the fluorescent powder, Zr independently occupies the site B of the hexa-coordination, which is intended to obtain an emission wavelength shorter than YAG. Because the ion radius (0.72 Å) of Zr 4+  is larger than the ion radius (0.535 Å) of Al 3+ , doping of the site B with a large-radius ion causes crystal cell volume expansion, and can weaken the crystal field where Ce 3+  is placed, thereby reducing the 5d energy level splitting degree and realizing short-wavelength emission. Moreover, B is Zr independently, the ion radius difference of the site B can be reduced, and the lattice stress is reduced, such that the garnet structure is more stable. 
         [0023]    The above structure refinement result shows that in the fluorescent powder of the application, Zr occupies the site B in the garnet structure. Therefore, the application eliminates relevancy to patent documents 3 and 6. The main difference between a patent document 5 and the application lies in that: Zr and an equal number of Mg or Zn are introduced to the site B at the same time in the patent document 5, and the site A only comprises trivalent rare-earth elements; however, the site B in the application only has Zr, and the site A must comprise bivalent alkaline-earth metal elements. In addition, the main difference between a patent document 4 and the application lies in that: the patent document 4 must comprise Al, and the synthetic temperature is higher than 1,500° C.; however, the application does not comprise Al but must comprise Ga, the synthetic temperature is lower than 1,400° C., and the application further includes: introducing bivalent metal elements (such as Ca and Sr) and tetravalent metal elements (such as Si and Ge) to the sites A and X respectively to further reduce the usage of rare-earth elements in the site A. 
         [0024]    In the fluorescent powder, an atom number ratio m of (Ca+Sr) to M 1  is: 2/3≦m≦1. Setting of this range is intended to reduce the usage of rare-earth elements and meet molecular charge balance. 
         [0025]    In the fluorescent powder, an atom number ratio n of Ce to M 2  is: 0.8≦n≦1. Setting of this range is intended to emphasize a principal role of Ce 3+  as an activating agent, so as to obtain fluorescent powder having excellent light emitting performance. 
         [0026]    In the fluorescent powder, an atom number ratio k of Ga to M 3  is: 2/3≦k≦1. Setting of this range is intended to stabilize a garnet phase. Since the ion radius and charge differences of Si, Ge and Ga are large, Ga is controlled to exceed 2/3, and fluorescent powder having a stable garnet structure can be obtained. 
         [0027]    In the fluorescent powder, Si and Ge are introduced into M 3  to be capable of replacing part of Ga and reducing the usage of rare-earth elements in M 1 , but the introduction amount does not exceed ⅓ of the total number of M 3  atoms, which plays a role in enhancing ultraviolet and near-ultraviolet excitation and realizing the continuous adjustability of emission wavelengths. 
         [0028]    In a word, setting of the ranges contributes to obtaining a stable garnet structure phase and fluorescent powder having excellent light emitting performance. 
         [0029]    Preferably, in the fluorescent powder having a garnet structure of the application, M 1  comprises Ca or Sr preferably. The preference solution may reduce the size difference of ions in the same site, thereby reducing the lattice stress, and contributing to stabilization of the garnet structure. 
         [0030]    More preferably, in the fluorescent powder having a garnet structure of the application, M 1  in the fluorescent powder comprises Ca preferably. Since the radius of Ca ions and rare-earth ions are close and well match a light emitting centre M 2 , and a fluorescent powder having a stable structure and better light emitting performance can be obtained favourably. 
         [0031]    In the fluorescent powder, parameters a, b, c and d are preferred as: a:b:c:d=3:2:3:12. Preference of the parameters in such ratio contributes to stabilization of a garnet phase and completeness of crystallization. 
         [0032]    A preparation method for the fluorescent powder may include the steps as follows.
       (1) serving compounds corresponding to M 1 , M 2 , M 3  and Zr as raw materials and egrounding and unifromly mixing the compounds;   (2) roasting a mixture obtained in Step (1) in a reducing atmosphere at high temperatures; and   (3) after-treating a roasted product obtained in Step (2), and the fluorescent powder is obtained.       
 
         [0036]    In Step (1), the compounds corresponding to the raw materials M 1 , M 2 , M 3  and Zr includes oxides, carbonates, oxalates and nitrates. 
         [0037]    In Step (2), high-temperature roasting is performed for one or several times, the roasting temperature ranges from 1,100° C. to 1400° C. at each time, and roasting lasts for 0.5 h to 20 h at each time. 
         [0038]    In Step (3), after-treatment includes crushing, grinding or/and classifying. 
         [0039]    In a word, the fluorescent powder involved in the application has excellent light emitting performance, and can realize emission from blue light to yellow-green light wave bands under the excitation of ultraviolet, near-ultraviolet and short-wavelength blue light by adjusting matrix components. 
         [0040]    In addition, the application also provides a light emitting device. The light emitting device includes a light source and fluorescent powder, and at least one kind of fluorescent powder may be selected from the abovementioned fluorescent powder and the fluorescent powder prepared using the abovementioned preparation method. 
         [0041]    Finally, the application also provides an image display device and an illumination device, wherein the image display device and the illumination device include the abovementioned light emitting device. 
         [0042]    The application has the advantages as follows:
       The fluorescent powder involved in the application has a wide effective excitation range, is suitable for being excited by ultraviolet, near-ultraviolet and short-wavelength blue light, and is high in applicability.   The fluorescent powder involved in the application can emit blue light-yellow green light under the excitation of ultraviolet, near-ultraviolet and short-wavelength blue light, and is high in light emitting efficiency.   The fluorescent powder of the application has a garnet structure, and the physical and chemical properties are very stable.   The synthetic temperature of the fluorescent powder involved in the application is low, the preparation process is simple, special reaction equipment is not needed, and industrialized production is convenient.       
 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0047]    The drawings of the specification, forming a part of the application, are intended to provide further understanding of the application. The schematic embodiments and illustrations of the application are intended to explain the application, and do not form improper limits to the application. In the drawings: 
           [0048]      FIG. 1  is an X-powder diffraction diagram of (Ca 2 La 0.96 ,Ce 0.04 )Zr 2 Ga 3 O 12 ; 
           [0049]      FIG. 2  is an excitation spectrum diagram of (Ca 2 La 0.96 ,Ce 0.04 )Zr 2 Ga 3 O 12 ; 
           [0050]      FIG. 3  is an emission spectrum diagram of (Ca 2 La 0.96 ,Ce 0.04 )Zr 2 Ga 3 O 12 ; 
           [0051]      FIG. 4  is an X-powder diffraction diagram of (Ca 2.91 ,Ce 0.06 )Zr 2 (Ga 2 Ge)O 12 ; 
           [0052]      FIG. 5  is an excitation spectrum diagram of (Ca 2.91 ,Ce 0.06 )Zr 2 (Ga 2 Ge)O 12 ; 
           [0053]      FIG. 6  is an emission spectrum diagram of (Ca 2.91 ,Ce 0.06 )Zr 2 (Ga 2 Ge)O 12 ; and 
           [0054]      FIG. 7  is an X-powder diffraction refinement pattern of (Ca 2 Y 0.94 , Ce 0.06 )Zr 2 Ga 3 O 12 . 
       
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
       [0055]    The following further illustrations of the embodiments for fluorescent powder of the application and a preparation method thereof will contribute to further understanding of the application. A protective range of the application is not limited by these embodiments, and the protective range thereof is decided by the claims. 
         [0056]    Comparing Sample 
         [0057]    0.2 mol of CaCO 3 , 0.05 ml of La 2 O 3 , 0.2 mol of ZrO 2  and 0.15 mol of Ga 2 O 3  are weighed according to a chemical formula (Ca 2 La)Zr 2 Ga 3 O 12 . After these raw materials are fully ground and uniformly mixed, an obtained mixture is roasted for 4 h at the temperature of 1,350° C. in a CO atmosphere. A roasted product is after-treated, including crushing, classifying, washing, drying, sieving and the like to obtain a compound having a composition: (Ca 2 La)Zr 2 Ga 3 O 12 . A sample is extracted for spectrum test, an emission spectrum being not seen under the excitation of ultraviolet and blue-light areas. The relative luminous intensity under the excitation of 420 nm is 0, as shown in Table 3. 
       Embodiment 1 
       [0058]    0.2 mol of CaCO 3 , 0.048 ml of La 2 O 3 , 0.2 mol of ZrO 2 , 0.15 mol of Ga 2 O 3  and 0.004 mol of CeO 2  are weighed according to a chemical formula (Ca 2 La 0.96 ,Ce 0.04 )Zr 2 Ga 3 O 12  of fluorescent powder. After these raw materials are fully ground and uniformly mixed, an obtained mixture is roasted for 4 h at the temperature of 1,350° C. in a CO atmosphere. A roasted product is after-treated, including crushing, classifying, washing, drying, sieving and the like to obtain fluorescent powder having a composition: (Ca 2 La 0.96 ,Ce 0.04 )Zr 2 Ga 3 O 12 . An X-powder diffraction diagram (Co target, λ=0.178892 nm) thereof is shown in  FIG. 1 . An excitation spectrum (515 nm monitoring) and an emission spectrum (420 nm excitation) thereof are shown in  FIG. 2  and  FIG. 3 . From the drawings, it can be obtained that an excitation wavelength range covers 280 to 480 nm, under the 420 nm excitation, the peak wavelength of the emission spectrum is 515 nm, and the relative luminous intensity is shown in Table 3. 
       Embodiment 2 
       [0059]    0.291 mol of CaCO 3 , 0.2 mol of ZrO 2 , 0.1 mol of GeO 2 , 0.1 mol of Ga 2 O 3  and 0.006 mol of CeO 2  are weighed according to a chemical formula (Ca 2.91 ,Ce 0.06 )Zr 2 (Ga 2 Ge)O 12  of fluorescent powder. After these raw materials are fully ground and uniformly mixed, an obtained mixture is roasted for 8 h at the temperature of 1,320° C. in a CO atmosphere. A roasted product is after-treated, including crushing, classifying, washing, drying, sieving and the like to obtain fluorescent powder having a composition: (Ca 2.91 ,Ce 0.06 )Zr 2 (Ga 2 Ge)O 12 . An X-powder diffraction diagram (Co target, λ=0.178892 nm) thereof is shown in  FIG. 4 . An excitation spectrum (475 nm monitoring) and an emission spectrum (420 nm excitation) thereof are shown in  FIG. 5  and  FIG. 6 . From the drawings, it can be obtained that an excitation wavelength range covers 280 to 440 nm, under the 420 nm excitation, the peak wavelength of the emission spectrum is 475 nm, and the relative luminous intensity is shown in Table 3. 
       Embodiment 3 
       [0060]    0.2 mol of CaCO 3 , 0.2 mol of ZrO 2 , 0.047 mol of Y 2 O 3 , 0.15 mol of Ga 2 O 3  and 0.006 mol of Ce(NO 3 ) 3  are weighed according to a chemical formula (Ca 2 Y 0.94 ,Ce 0.06 )Zr 2 Ga 3 O 12  of fluorescent powder. After these raw materials are fully ground and uniformly mixed, an obtained mixture is roasted for 6 h at the temperature of 1,360° C. in an H 2 /N 2  mixed atmosphere. A roasted product is after-treated, including crushing, classifying, washing, drying, sieving and the like to obtain fluorescent powder having a composition: (Ca 2 Y 0.94 ,Ce 0.06 )Zr 2 Ga 3 O 12 . X-powder ray diffraction refinement fitting parameters thereof are shown in Table 1 and Table 2. Fitting of a pattern is shown in  FIG. 7 . An excitation wavelength range covers 280 to 480 nm, under the 420 nm excitation, the peak wavelength of the emission spectrum is 512 nm, and the relative luminous intensity is shown in Table 3. 
       Embodiment 4 
       [0061]    0.2 mol of CaCO 3 , 0.2 mol of ZrO 2 , 0.046 mol of Lu 2 O 3 , 0.15 mol of Ga 2 O 3  and 0.008 mol of CeO 2  are weighed according to a chemical formula (Ca 2 Lu 0.92 ,Ce 0.08 )Zr 2 Ga 3 O 12  of fluorescent powder. After these raw materials are fully ground and uniformly mixed, an obtained mixture is roasted for 4 h at the temperature of 1,100° C. in air. A roasted product is crushed and then secondarily roasted for 6 h at the sintering temperature of 1,350° C. in a CO atmosphere. A secondarily roasted product is after-treated, including crushing, classifying, washing, drying, sieving and the like to obtain fluorescent powder having a composition: (Ca 2 Lu 0.92 ,Ce 0.08 )Zr 2 Ga 3 O 12 . An excitation wavelength range covers 280 to 480 nm, under the 420 nm excitation, the peak wavelength of the emission spectrum is 502 nm, and the relative luminous intensity is shown in Table 3. 
       Embodiment 5 
       [0062]    0.2 mol of CaCO 3 , 0.045 mol of Gd 2 O 3 , 0.2 mol of ZrO 2 , 0.15 mol of Ga 2 O 3  and 0.01 mol of CeO 2  are weighed according to a chemical formula (Ca 2 Gd 0.9 ,Ce 0.1 )Zr 2 Ga 3 O 12  of fluorescent powder. After these raw materials are fully ground and uniformly mixed, an obtained mixture is roasted for 6 h at the temperature of 1,400° C. in an H 2 /N 2  mixed atmosphere. A roasted product is after-treated, including crushing, classifying, washing, drying, sieving and the like to obtain fluorescent powder having a composition: (Ca 2 Gd 0.9 ,Ce 0.1 )Zr 2 Ga 3 O 12 . An excitation wavelength range covers 280 to 480 nm, under the 420 nm excitation, the peak wavelength of the emission spectrum is 514 nm, and the relative luminous intensity is shown in Table 3. 
       Embodiment 6 
       [0063]    0.275 mol of CaCO 3 , 0.01 mol of SrCO 3 , 0.2 mol of ZrO 2 , 0.02 mol of SiO 2 , 0.1 mol of Ga 2 O 3 , 0.08 mol of GeO 2  and 0.01 mol of CeO 2  are weighed according to a chemical formula (Ca 2.75 Sr 0.1 ,Ce 0.1 )Zr 2 (Ga 2 Ge 0.8 Si 0.2 )O 12  of fluorescent powder. After these raw materials are fully ground and uniformly mixed, an obtained mixture is roasted for 0.5 h at the temperature of 1,200° C. in air. A primarily roasted product is crushed and then secondarily roasted for 6 h at the sintering temperature of 1,320° C. in a CO atmosphere. A secondarily roasted product is after-treated, including crushing, classifying, washing, drying, sieving and the like to obtain fluorescent powder having a composition: (Ca 2.75 Sr 0.1 ,Ce 0.1 )Zr 2 (Ga 2 Ge 0.8 Si 0.2 )O 12 . An excitation wavelength range covers 280 to 460 nm, under the 420 nm excitation, the peak wavelength of the emission spectrum is 482 nm, and the relative luminous intensity is shown in Table 3. 
       Embodiment 7 
       [0064]    0.25 mol of CaCO 3 , 0.0225 mol of Lu 2 O 3 , 0.2 mol of ZrO 2 , 0.05 mol of SiO 2 , 0.125 mol of Ga 2 O 3 , 0.0005 mol of Eu 2 O 3  and 0.004 mol of CeO 2  are weighed according to a chemical formula (Ca 2.5 Lu 0.45 ,Ce 0.04 Eu 0.01 )Zr 2 (Ga 2.5 Si 0.5 )O 12  of fluorescent powder. After these raw materials are fully ground and uniformly mixed, an obtained mixture is roasted for 8 h at the temperature of 1,400° C. in a CO atmosphere. A roasted product is after-treated, including crushing, classifying, washing, drying, sieving and the like to obtain fluorescent powder having a composition: (Ca 2.5 Lu 0.45 ,Ce 0.04 Eu 0.01 )Zr 2 (Ga 2.5 Si 0.5 )O 12 . An excitation wavelength range covers 280 to 480 nm, under the 420 nm excitation, the peak wavelength of the emission spectrum is 493 nm, and the relative luminous intensity is shown in Table 3. 
       Embodiment 8 
       [0065]    0.2997 mol of CaCO 3 , 0.2 mol of ZrO 2 , 0.1 mol of SiO 2 , 0.1 mol of Ga 2 O 3  and 0.0002 mol of CeO 2  are weighed according to a chemical formula (Ca 2.997 ,Ce 0.002 )Zr 2 (Ga 2 Si)O 12  of fluorescent powder. After these raw materials are fully ground and uniformly mixed, an obtained mixture is roasted for 4 h at the temperature of 1,380° C. in a CO atmosphere. A roasted product is after-treated, including crushing, classifying, washing, drying, sieving and the like to obtain fluorescent powder having a composition: (Ca 2.997 ,Ce 0.002 )Zr 2 (Ga 2 Si)O 12 . An excitation wavelength range covers 280 to 450 nm, under the 420 nm excitation, the peak wavelength of the emission spectrum is 487 nm, and the relative luminous intensity is shown in Table 3. 
       Embodiment 9 
       [0066]    0.24 mol of CaCO 3 , 0.19 mol of ZrO 2 , 0.0375 mol of Y 2 O 3 , 0.14 mol of Ga 2 O 3 , 0.004 mol of CeO 2  and 0.00017 mol of Pr 6 O 11  are weighed according to a chemical formula (Ca 2.4 Y 0.75 ,Ce 0.04 Pr 0.01 )Zr 1.9 Ga 2.8 O 11.8  of fluorescent powder. After these raw materials are fully ground and uniformly mixed, carbon powder is added, and an obtained mixture is roasted for 15 h at the temperature of 1,350° C. A roasted product is after-treated, including crushing, classifying, washing, drying, sieving and the like to obtain fluorescent powder having a composition: (Ca 2.4 Y 0.75 ,Ce 0.04 Pr 0.01 )Zr 1.9 Ga 2.8 O 11.8 . An excitation wavelength range covers 280 to 480 nm, under the 420 nm excitation, the peak wavelength of the emission spectrum is 510 nm, and the relative luminous intensity is shown in Table 3. 
       Embodiment 10 
       [0067]    0.2 mol of SrCO 3 , 0.035 mol of Gd 2 O 3 , 0.21 mol of ZrO 2 , 0.16 mol of Ga 2 O 3 , 0.008 mol of CeO 2  and 0.001 mol of Dy 2 O 3  are weighed according to a chemical formula (Sr 2 Gd 0.7 ,Ce 0.08 Dy 0.02 )Zr 2.1 Ga 3.2 O 12.2  of fluorescent powder. After these raw materials are fully ground and uniformly mixed, an obtained mixture is roasted for 20 h at the temperature of 1,400° C. in a CO atmosphere. A roasted product is after-treated, including crushing, classifying, washing, drying, sieving and the like to obtain fluorescent powder having a composition: (Sr 2 Gd 0.7 ,Ce 0.08 Dy 0.02 )Zr 2.1 Ga 3.2 O 12.2 . An excitation wavelength range covers 280 to 480 nm, under the 420 nm excitation, the peak wavelength of the emission spectrum is 526 nm, and the relative luminous intensity is shown in Table 3. 
       Embodiment 11 
       [0068]    0.294 mol of SrCO 3 , 0.1 mol of SiO 2 , 0.2 mol of ZrO 2 , 0.1 mol of Ga 2 O 3  and 0.004 mol of CeO 2  are weighed according to a chemical formula (Sr 2.94 ,Ce 0.04 )Zr 2 (Ga 2 Si)O 12  of fluorescent powder. After these raw materials are fully ground and uniformly mixed, an obtained mixture is roasted for 6 h at the temperature of 1,300° C. in air. A roasted product is crushed and then secondarily roasted for 10 h at the sintering temperature of 1,400° C. in a CO/N 2  atmosphere. A secondarily roasted product is after-treated, including crushing, classifying, washing, drying, sieving and the like to obtain fluorescent powder having a composition: (Sr 2.94 ,Ce 0.04 )Zr 2 (Ga 2 Si)O 12 . An excitation wavelength range covers 280 to 480 nm, under the 420 nm excitation, the peak wavelength of the emission spectrum is 494 nm, and the relative luminous intensity is shown in Table 3. 
       Embodiment 12 
       [0069]    0.2 mol of SrCO 3 , 0.2 mol of ZrO 2 , 0.0475 mol of La 2 O 3 , 0.15 mol of Ga 2 O 3  and 0.005 mol of CeO 2  are weighed according to a chemical formula (Sr 2 La 0.95 ,Ce 0.05 )Zr 2 Ga 3 O 12  of fluorescent powder. After these raw materials are fully ground and uniformly mixed, an obtained mixture is roasted for 6 h at the temperature of 1,200° C. in air. A roasted product is crushed and then secondarily roasted for 2 h at the sintering temperature of 1,370° C. in an H 2 /N 2  atmosphere. A secondarily roasted product is after-treated, including crushing, classifying, washing, drying, sieving and the like to obtain fluorescent powder having a composition: (Sr 2 La 0.95 ,Ce 0.005 )Zr 2 Ga 3 O 12 . An excitation wavelength range covers 280 to 480 nm, under the 420 nm excitation, the peak wavelength of the emission spectrum is 535 nm, and the relative luminous intensity is shown in Table 3. 
       Embodiment 13 
       [0070]    0.2 mol of CaCO 3 , 0.2 mol of ZrO 2 , 0.02 mol of Y 2 O 3 , 0.15 mol of Ga 2 O 3 , 0.05 mol of CeO 2  and 0.0025 mol of Tb 4 O 7  are weighed according to a chemical formula (Ca 2 Y 0.4 ,Ce 0.5 Tb 0.1 )Zr 2 Ga 3 O 12  of fluorescent powder. After these raw materials are fully ground and uniformly mixed, an obtained mixture is roasted for 4 h at the temperature of 1,350° C. in a CO atmosphere. A roasted product is after-treated, including crushing, classifying, washing, drying, sieving and the like to obtain fluorescent powder having a composition: (Ca 2 Y 0.4 ,Ce 0.5 Tb 0.1 )Zr 2 Ga 3 O 12 . An excitation wavelength range covers 280 to 450 nm, under the 420 nm excitation, the peak wavelength of the emission spectrum is 542 nm, and the relative luminous intensity is shown in Table 3. 
       Embodiment 14 
       [0071]    0.28 mol of CaCO 3 , 0.2 mol of ZrO 2 , 0.08 mol of SiO 2 , 0.008 mol of Gd 2 O 3 , 0.11 mol of Ga 2 O 3  and 0.004 mol of CeO 2  are weighed according to a chemical formula (Ca 2.8 Gd 0.16 ,Ce 0.04 )Zr 2 (Ga 2.2 Si 0.8 )O 12  of fluorescent powder. After these raw materials are fully ground and uniformly mixed, an obtained mixture is roasted for 6 h at the temperature of 1,320° C. in a CO atmosphere. A roasted product is after-treated, including crushing, classifying, washing, drying, sieving and the like to obtain fluorescent powder having a composition: (Ca 2.8 Gd 0.16 ,Ce 0.04 )Zr 2 (Ga 2.2 Si 0.8 )O 12 . An excitation wavelength range covers 280 to 450 nm, under the 420 nm excitation, the peak wavelength of the emission spectrum is 492 nm, and the relative luminous intensity is shown in Table 3. 
       Embodiment 15 
       [0072]    0.22 mol of SrCO 3 , 0.2 mol of ZrO 2 , 0.02 mol of SiO 2 , 0.0365 mol of La 2 O 3 , 0.14 mol of Ga 2 O 3 , 0.005 mol of CeO 2  and 0.001 mol of Sm 2 O 3  are weighed according to a chemical formula (Sr 2.2 La 0.73 ,Ce 0.05 Sm 0.02 )Zr 2 (Ga 2.8 Si 0.2 )O 12  of fluorescent powder. After these raw materials are fully ground and uniformly mixed, an obtained mixture is roasted for 6 h at the temperature of 1,200° C. in air. A roasted product is crushed and then secondarily roasted for 2 h at the sintering temperature of 1,380° C. in an H 2 /N 2  atmosphere. A secondarily roasted product is after-treated, including crushing, classifying, washing, drying, sieving and the like to obtain fluorescent powder having a composition: (Sr 2.2 La 0.73 ,Ce 0.05 Sm 0.02 )Zr 2 (Ga 2.8 Si 0.2 )O 12 . An excitation wavelength range covers 280 to 480 nm, under the 420 nm excitation, the peak wavelength of the emission spectrum is 524 nm, and the relative luminous intensity is shown in Table 3. 
       Embodiment 16 
       [0073]    Green fluorescent powder obtained in Embodiment 1 and red powder of K 2 SiF 6 :Mn are scattered in resin in a ratio of 7:1, and after being mixed, the slurry is coated on a 450 nm blue-light LED chip, solidified, welded to a circuit and sealed by the resin to obtain a light emitting device emitting white light, the chromaticity coordinate being (0.3885, 0.3692), the colour rendering index being 87.2, and the correlated colour temperature being 3624K. 
       Embodiment 17 
       [0074]    Blue fluorescent powder obtained in Embodiment 2, β-SiAlON:Eu green fluorescent powder and CaAlSiN 3 :Eu red fluorescent powder are scattered in resin in a ratio of 3:6:1, and after being mixed, the slurry is coated on a 405 nm ultraviolet LED chip, solidified, welded to a circuit and sealed by the resin to obtain a light emitting device emitting white light, the chromaticity coordinate being (0.3963, 0.3785), and the colour reproduction range being 80% NTSC. 
       Embodiment 18 
       [0075]    Blue fluorescent powder obtained in Embodiment 7, green fluorescent powder obtained in Embodiment 13 and (Sr,Ca) 2 Si 5 N 8 :Eu red fluorescent powder are scattered in resin in a ratio of 4:7:1, and after being mixed, the slurry is coated on a 405 nm ultraviolet LED chip, solidified, welded to a circuit and sealed by the resin to obtain a light emitting device emitting white light, the chromaticity coordinate being (0.3796, 0.3589), the colour rendering index being 85.6, and the correlated colour temperature being 4230K. 
         [0000]    
       
         
               
             
               
               
               
               
             
               
               
               
               
             
           
               
                 TABLE 3 
               
             
             
               
                   
               
               
                 Chemical formulae of comparing example and Embodiments 1-15, and 
               
               
                 emission main peak position and relative luminous intensity under 420 nm excitation 
               
               
                 (the luminous intensity of Ca 2 La 0.96 Zr 2 Ga 3 O 12 :Ce 0.04  is selected to be 100% under the 
               
               
                 420 nm excitation) 
               
             
          
           
               
                   
                   
                 Emission 
                 Relative 
               
               
                   
                   
                 main peak 
                 luminous 
               
               
                   
                 Chemical formula of fluorescent 
                 position 
                 intensity 
               
               
                 Serial number 
                 powder 
                 (nm) 
                 (%) 
               
               
                   
               
             
          
           
               
                 Comparing 
                 (Ca 2 La)Zr 2 Ga 3 O 12   
                 Null 
                 0 
               
               
                 example 
               
               
                 Embodiment 1 
                 (Ca 2 La 0.96 ,Ce 0.04 )Zr 2 Ga 3 O 12   
                 515 
                 100 
               
               
                 Embodiment 2 
                 (Ca 2.91 ,Ce 0.06 )Zr 2 (Ga 2 Ge)O 12   
                 475 
                 112 
               
               
                 Embodiment 3 
                 (Ca 2 Y 0.94 ,Ce 0.06 )Zr 2 Ga 3 O 12   
                 512 
                 105 
               
               
                 Embodiment 4 
                 (Ca 2 Lu 0.92 ,Ce 0.08 )Zr 2 Ga 3 O 12   
                 502 
                 101 
               
               
                 Embodiment 5 
                 (Ca 2 Gd 0.9 ,Ce 0.1 )Zr 2 Ga 3 O 12   
                 514 
                 102 
               
               
                 Embodiment 6 
                 (Ca 2.75 Sr 0.1 ,Ce 0.1 )Zr 2 (Ga 2 Ge 0.8 Si 0.2 )O 12   
                 482 
                 95 
               
               
                 Embodiment 7 
                 (Ca 2.5 Lu 0.45 ,Ce 0.04 Eu 0.01 )Zr 2 (Ga 2.5 Si 0.5 )O 12   
                 493 
                 107 
               
               
                 Embodiment 8 
                 (Ca 2.997 ,Ce 0.002 )Zr 2 (Ga 2 Si)O 12   
                 487 
                 98 
               
               
                 Embodiment 9 
                 (Ca 2.4 Y 0.75 ,Ce 0.04 Pr 0.01 )Zr 1.9 Ga 2.8 O 11.8   
                 510 
                 102 
               
               
                 Embodiment 10 
                 (Sr 2 Gd 0.7 ,Ce 0.08 Dy 0.02 )Zr 2.1 Ga 3.2 O 12.2   
                 526 
                 96 
               
               
                 Embodiment 11 
                 (Sr 2.94 ,Ce 0.04 )Zr 2 (Ga 2 Si)O 12   
                 494 
                 103 
               
               
                 Embodiment 12 
                 (Sr 2 La 0.95 ,Ce 0.05 )Zr 2 Ga 3 O 12   
                 535 
                 96 
               
               
                 Embodiment 13 
                 (Ca 2 Y 0.4 ,Ce 0.5 Tb 0.1 )Zr 2 Ga 3 O 12.   
                 542 
                 106 
               
               
                 Embodiment 14 
                 (Ca 2.8 Gd 0.16 ,Ce 0.04 )Zr 2 (Ga 2.2 Si 0.8 )O 12   
                 492 
                 102 
               
               
                 Embodiment 15 
                 (Sr 2.2 La 0.73 ,Ce 0.05 Sm 0.02 )Zr 2 (Ga 2.8 Si 0.2 )O 12   
                 524 
                 97