Ulllted States Patent [19] [11] Patent Number: 6,117,362. Yen et al. [45] Date of Patent: Sep. 12, 2000

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1 US A Ulllted States Patent [19] [11] Patent Number: 6,117,362 Yen et al. [45] Date of Patent: Sep. 12, 2000 [54] LONG-PERSISTENCE BLUE PHOSPHORS OTHER PUBLICATIONS [75] Inventors: William M_ Yen, Athens, Ga_; Weiyi Abbruscato et al. (1971), Optical and Electrical Properties Jia, Mayaquez, puerto Rico; Lizhu Lu; of SrAl2O4:Eu2+ J. Electrochem. Soc. 118(6): Huabiao Yuan, both of Athens, Ga_ Autrata, R. et al. (1983), Single Crystal Aluminates A NeW Generation of Scintillators for Scanning Electron [73] Assignees; University of Georgia Research Microscopes and Transparent Screens in Electron Optical Foundation, Inc, Atlanta, Ga_; Devices, Scanning Electron. Microsc., pp University of Puerto Rico, San Juan, Babitskaya, RA. et al. (1981), Improvement and develop Puerto Rico ment of new effective luminophors having green and blue luminescence for gas discharge indicator panels, Chemical [21] Appi NO; 09/187,944 Abstracts 96:112888j (1982). _ Chen, R. and McKeever, S.W.S. (1997), Theory of Ther [22] Flled: NOV moluminescence and Related Phenomena, World Scienti?c, Singapore, pp [60] provisioliflllglicgii'ligpéggzfgggzg?v and Chemekova~ et al-th(1977) TerZiSy Dokl. Uses. Soveshch. provisional application No. 60/064,691, Nov. 7: lgzgsgglé- zg?ilst- 5 2Z (Chem. Abst, (1980) [51] Int. Cl C09K 11/55; C09K 11/64 czochraiski, J_ (1918), Em neues Verfahren Zur Messung U-S- Cl /946 def Chem. KristanisationsgeSchwindigkeit 92: def Metalle, [58] Field of Search /3014 R; 117/946, 117/950 (List continued on next page.). Primary Examiner C. Melissa KosloW [56] References Clted Attorney, Agent, or Firm Greenlee, Winner and Sullivan, U.S. PATENT DOCUMENTS P-C 3,294,699 12/1966 Lange /301.4 R [57] ABSTRACT 4,110,660 4,249,108 8/1978 Wolfe 2/1981 Wolfe 313/ /486 This invention relates to phosphors including long 4,623,816 11/1986 Hoffman et al /487 persistence blue phosphors. Phosphors of the invention are 4,733,126 3/1988 Yamakawa et al. 313/487 represented by the general formula: 5,350,971 9/1994 Jeong /487 5,358,734 10/1994 LenoX et al /71 MO. mal2o3:eu2",r3+ 5,376,303 12/1994 Royce et al /301.4 R 5,424,006 FOREIGN 6/1995 PATENT Murayama DOCUMENTS et al /3014 R wherein is Sr or [n a is combination a number ranging of Sr With from Ca about and Ba [0 or about both, R3+ 1s a trivalent metal ion or trivalent B1 or a mixture of these /1990 European Pat. Off. _ trivalent ions, Eu2+ is present at a level up to about 5 mol % O A2 3/1991 European Pat. Off.. of M, and R3+ is present at a level up to about 5 mol % of A1 6/1996 European Pat Off- - M. Phosphors of this invention include powders, ceramics, A1 4/1997 European Pat O?- - single crystals and single crystal?bers. A method of manu /1976 Japan ' facturing improved phosphors and a method of manufactur /1982 Japan ' /1993 Japan. ing single crystal phosphors are also provided /1994 Japan /1994 Japan. 30 Claims, 16 Drawing Sheets I 6000 a after 55:20 a after 20sec A after 60sec Intensity ( a.u.) Wavelength ( nm )

6,117,362 Page 2 OTHER PUBLICATIONS Jia, W. (1998), Phosphorescent dynamics in SrAi2O4:Eu2+, Dy3+ single crystal?bers, J. Luminescence 76 & 77:424 428. Katsumata, T. et al.

2 6,117,362 Page 2 OTHER PUBLICATIONS Jia, W. (1998), Phosphorescent dynamics in SrAi2O4:Eu2+, Dy3+ single crystal?bers, J. Luminescence 76 & 77: Katsumata, T. et al. (1998), Growth and characteristics of long persistent SrAl2O4 and CaAl2O4 based phosphor crystals by a?oating Zone technique, J. Cryst. GroWth 183: Katsumata, T. et al. (1998), Characteristics of Strontium Aluminate Crystals Used for Long Duration Phosphors, J. Am. Ceram. Soc. 81: Katsumata, T. et al. (1997), Effects of Composition on the Long Phosphorescent SrAl2O4:Eu2+, Dy3+ Phosphor Crys tals, J. Electrochem. Soc. 144(9):L243 L245. Kutty, T.R. et al. (1990), Luminescence of the Eu2+ in Strontium Aluminates Prepared by the Hydrothermal Method, Mater. Res. Bull. 25: MatsuZaWa, T. et al. (1996), A NeW Long Phosphorescent Phosphor With High Brightness, SrAl2O4:Eu2+,Dy3+, J. Electrochem. Soc. 143(8):2670. Ondracek, J. and Bohumil, H. (1991), Some?ndings on blue emitting luminophore based on (barium, europium (2+)) magnesium aluminate, Chemical Abstracts 116:161516b (1992). Palilla, EC. et al. (1968), Fluorescent Properties of Alka line Earth Aluminates of the Type MAIZO4 Activated by Divalent Europium, J. Electrochem. Soc. 115(6): Pfann, W.G. (1952), Principles of Zone Melting, Trans. AIME 194: Shinoya, S. (1998) in Phosphor Handbook, Shinoya, S. and Yen, W.M. (eds.), CRC Press, Inc., Boca Raton, NeW York, p. 3. Smets, B. et al. (1989), 2SrO-3Al2O3:Eu2+ and 1.29(Ba, Ca)O,6Al2O3:Eu2+. TWo NeW Blue Emitting Phosphors, J. Electrochem. Soc. 136(7): Sonoda, M. et al. (1983), Computed Radiography UtiliZing Scanning Laser Stimulated Luminescence, Radiology 148: Tissue, B.M. et al. (1991), Laser heated pedestal growth of laser and IR upconverting materials, J. Cryst. GroWth 109: Yen, W.M. (1995) Preparation of single crystal?bers, in Insulating Materials for Optoelectronics, F. Agullo LopeZ, ed., World Scienti?c, Singapore, Chapter 2, p. 77. Zlotnikova et al. (1990) Ukr. Khim Zh. (Russ. Ed.) 56(11): (Chem. Abst. (1991)115;3779s1<). Zorencko, Yu. V. et al. (1991), The Peculiarities of Receiv ing of Thin Film Single Crystal Oxide Luminophores, Cryst. Properties and Preparation 36 38:

3 U.S. Patent Sep. 12,2000 Sheet 1 0f 16 6,117,362 6 O O 0 _ after 5sec after20sec after60sec A 36:25 V m 40 O O _ Wavelength ( nm ) 600 FIG. 1

4 U.S. Patent Sep. 12,2000 Sheet 2 0f 16 6,117,362 I I I ITIIIVI T I I IITTTT I I I I II'III I 106 :- E 105 F E 3:.. (U ". B104 F '5 : : C ' - q, _ - H - - E _ - E 103 :- E I l lllll l I l Lllllll I I l Illlll I Delay Time ( minute ) FIG. 2

5 U.S. Patent Sep. 12,2000 Sheet 3 0f 16 6,117,362 _ Excitation Emission _ f? (a.u Intensity l l I l a I l l f Wavelength (nm) FIG. 3

6 U.S. Patent Sep. 12,2000 Sheet 4 0f 16 6,117,362 (s /s1unoo) mgsuelul

7 U.S. Patent Sep. 12,2000 Sheet 5 0f 16 6,117, I O 0 after 5sec after20sec after 60sec O 0 O _ V 36:25.:.m Wavelength ( nm ) 600 FIG. 5

8 U.S. Patent Sep. 12,2000 Sheet 6 0f 16 6,117,362 I IIIIIII' I I TI! III I IIIIIITI l IIIIIII I Illllll I l )( Intensity a.u. "<1 Illllll """l ' lllllll l mull l I I l Illllll I I lllllll l I LLIIIII l Delay Time ( minute ) FIG. 6

9 U.S. Patent Sep. 12,2000 Sheet 7 0f 16 6,117, " Excitation Emission (a.u.) Intensity l A. l Wavelength (nm) FIG. 7

10 U.S. Patent Sep. 12,2000 Sheet 8 0f 16 6,117,362 I I I I l l l I I D C D after 5sec after 20sec after 60sec () Intensity a.u Wavelength ( nm ) FIG. 8

11 U.S. Patent Sep. 12,2000 Sheet 9 0f 16 6,117,362 I I I IIIII' I I I IIIIIl I I IIIIIII I E 105 E ': m -. v 4 Q10 = 5 w :. c - I m l E. 103 E- _:. 2 l I l Illlll l l l llllll l l l Illlll I Delay Time ( minute) FIG. 9

12 U.S. Patent Sep. 12, 2000 Sheet 10 0f 16 6,117, Excitation Emission (a.u.) intensity I I l I l I I I l I I I l I l I Wavelength (nm) FIG. 10

13 U.S. Patent Sep. 12,2000 Sheet 11 0f 16 6,117,362 30x104 Y. X Q + I Nd La Lu Tb Gd Sm AOX D O Er Ce Yb Dy Tm A v 36:35.:.m A UYEWRIOO gum! O. *I O. 038.] O9 V gle 10 Time ( second ) FIG. 11

14 U.S. Patent Sep. 12,2000 Sheet 12 0f 16 6,117,362 uniqu A v 35:25.:.m Time ( second ) 3000 FIG. 12

15 U.S. Patent Sep. 12,2000 Sheet 13 0f 16 6,117, Excitation Emission (a.u.) Intensity I.. 1. l Wavelength (nm) FIG. 13

16 U.S. Patent Sep. 12, 2000 Sheet 14 0f 16 6,117,362 I I IIIIII' I I IIIIII' I I IIIIIII I L IIIIII' lllllll l 105 BI : : CU " -\ v _. > I : 4 u) 10 :- '5 C : I Q) E :- _: I llllllll l l IlllIlI l llllllli L Delay Time ( minute ) FIG. 14

17 U.S. Patent Sep. 12,2000 Sheet 15 0f 16 6,117, after 5sec after 20sec after 60sec V 36:25 A.:.m _ 4 05 O Wavelength ( nm ) 600 FIG. 15

18 U.S. Patent Sep. 12,2000 Sheet 16 0f 16 6,117, O 0 _ after 5sec after 20sec after 60sec 4000 A V 56:25.:.m Wavelength ( nm ) FIG

1 LONG-PERSISTENCE BLUE PHOSPHORS CROSS-REFERENCE TO RELATED APPLICATIONS This application takes priority under 35 USC 119(e) from US. provisional applications Ser. No. 60/064,690,?led Nov.

19 1 LONG-PERSISTENCE BLUE PHOSPHORS CROSS-REFERENCE TO RELATED APPLICATIONS This application takes priority under 35 USC 119(e) from US. provisional applications Ser. No. 60/064,690,?led Nov. 7, 1997 and Ser. No. 60/064,691,?led 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 US. government funding through NASA grant MURC-NCCW 0088 and NCC5 252, ARO DAAH and DOE DE-FG02 94ER The United States government has certain rights in this invention. FIELD OF THE INVENTION This invention is generally related to phosphors and more particularly is related to long-persistence blue phosphors. The invention is also directed to methods for making phos phors in powder and ceramic form as Well as single crystal phosphors. The invention is further directed to articles of manufacture comprising the phosphors of this invention. 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 persistent green phosphor, SrAl2O4:Eu2":Dy3+ has been produced. Strong green luminescence from Eu2+-doped SrAl2O4 Was reported by H. Lange in Belgian patent 1,347,45 and US. Pat. No. 3,294,696. Ef?cient luminescence in the spectral range nm Was also reported from Eu2+ doped CaAl2O4, MgAl2O4, BaAl2O4, and SrAl2O4 and their counterparts C. Palilla, A. using K. alkaline Levine earth and M. cationic R. Tomkus combinations. (1968) J. Electrochem. Soc. 115:642). Long lasting and more ef?cient phosphorescence has obtained in Eu2+ doped SrAl2O4 synthesized With excess alumina Which results in formation of trapping centers associated With the Sr+2 vacancy (Abbruscato et al. (1971) J. Electrochem. Soc. 118:930). Improved long persistence phosphors of certain alkaline earth aluminates Were reported by T. MatsuZaWa, Y. Aoki, N. Takeuchi and Y. Murayama (1996) J. Electrochem. Soc. 143(8):2670, and in US. Pat. No. 5,424,006. The brightness and persistence time of SrAl2O4:Eu2+ Was improved by co-doping various trivalent rare earth ions to produce appro priate trapping centers. The best result Was obtained by co-doping Dy+3 With Eu+2 into SrAl2O4 and Nd3+ With Eu2+ into CaAl2O4 to get long persistent green and purple emission, respectively. US. Pat. No. 5,424,006 also reports phosphors in Which Mg2+ is substituted for Sr2+ in SrAl2O4:Eu2+, Dy3+. EP published application 765,925 (Moriyama et al.) reports Eu2+-activated strontium aluminate phosphors in Which part of the Sr2+ of the host is replaced With Pb3+, Dy3+ or Zn. The Zinc-doped materials are reported to display enhanced brightness and persistence compared to SrAl2O4:Eu2+, Dy3+. EP published application 710,709 (Murayama et al.) reports phosphors of matrix M1 XAl2O4_x Where M is at least one metal selected from calcium, strontium, barium and, optionally, magnesium, and X is a number not equal to 0. The matrix comprises europium as an activator and a co-activator elected from a rare earth metal, manganese, tin or bismuth. 6,117, JP Patent (1976, Tokyo Shibaura Electric Co.) reports blue-emitting phosphors containing barium (or cal cium or strontium)-potassium (or sodium) aluminates acti vated With europium and manganese. JP Patent (1994, Matsushita Electronics) reports a strontium aluminate phosphor activated With europium modi?ed by incorporation of yttrium oxide. JP Patent (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): (Chem. Abst. (1991) 115:37798k) reports composition dependence of catho-luminescent properties of a Dy-doped SrAl2O4 Sr Al4O7 system. T. R. Kutty et al. (1990) Mater. Res. Bull. 25: reports luminescence of Eu2+, in strontium aluminates pre pared by the hydrothermal method. Blue to green lumines cent phosphors of general formula SrnAl2O3+n Where n 1 are reported. The reference also reports the preparation of certain aluminoborates. B. Smets et al. (1989) J. Electrochem. Soc. 136(7) : reports blue-emitting phosphors: 2SrO. 3Al2O3:Eu2+ and 1.29 (Ba, Ca)O, 6 Al2O3:Eu2+. In the background section of the reference the authors refer to an earlier report of blue-green emitting phosphors 4SrO. 7Al2O3:Eu2+ and BaO. 4Al2O3:Eu2+, Which could be syn thesized only in the presence of small amounts of B203. Chemekova et al. (1977) TerZisy Dokl. Uses. Soveshch. Rostu. Krist. 5th 2: (Chem. Abst. (1980) 93:85423h) reports synthesis of single crystals in the cal cium oxide-alumina system. Addition of europium is said to produce phosphors. SUMMARY OF THE INVENTION This invention relates to long-persistent phosphors of general formula: Where M is Sr or a combination of Sr With Ca and/or Ba; R3+ is a trivalent rare earth metal ion or Bi3+, or mixtures of these trivalent metal ions; and m is a number ranging from about 1.6 to about 2.2. The phosphors are prepared using a?ux, particularly B203. The preferred phosphor formula of this invention indicating the presence of B2O3?uX is: Where M, m and R3+ are as de?ned in formula 1 and Z is a number ranging from about 0.02 to about 0.2. The phosphors of this invention comprise an alkaline earth aluminate matrix activated With Eu2+ and doped With certain trivalent metal ions R3". The phosphors are activated With about 0.02 mol % to about 10 mol % (preferably about 0.2 mol % to about 1.0 mol %) of Eu2+, activator and co-doped With about 0.02 mol % to about 20 mol % (preferably about 0.2 mo. % to about 2 mol %) to of at least one trivalent rare earth metal ion or Bi3+. The activator and dopant concentration are measured in terms of mol % relative to the alkaline earth metal element, M. Preferred phosphors of this invention are blue With a phosphorescent band at about 488 nm. Phosphors of this invention have signi?cantly improved brightness compared to sul?de phosphors, such as CaSrS:Bi. Phosphors of this invention can have persistence times up to about 18 hr. The phosphors of this invention are chemically stable, resistant to moisture and UV radiation and are believed to be relatively harmless to the environment.

3 Preferred phosphors of this invention are those in Which M is Sr. Phosphors of this invention are activated With Eu2+ and are codoped With a trivalent rare earth metal ion or Bi3+.

20 3 Preferred phosphors of this invention are those in Which M is Sr. Phosphors of this invention are activated With Eu2+ and are codoped With a trivalent rare earth metal ion or Bi3+. The phosphors may be codoped With a single ion or a combina tion of such ions selected from the group of rare earth metal ions: Pr3+, H03", Nd3+, Dy3+, Er3+, La3+, Lu3+, Ce3+, Y3", Sm3+, Gd3+, Tb3+, Tm3+, and Yb3+ and the Group VA metal ion Bi3+. Preferred trivalent dopants are Pr3+, H03", Dy3+, and Nd3+. Co-doping of Dy3+ or Y3+ With another trivalent metal ion results in phosphor of improved brightness, e.g. MAl4O7:Eu2+, Pr3+, Dy3+ or MAl4O7:Eu2+, H03", Dy3+. Preferred phosphors are those With m ranging from about 1.70 to about 2.05 and, more preferred, are those Where m=1.75, the host material being M4Al14O25 and m=2, the host material being MAl4O7. More preferred are phosphors Where M=Sr and m=1.75 or m=2. Phosphors of this invention also include those in Which Mg2+ or Zn2+, or a mixture of both, is substituted for Al3+ in the matrix material and Where M2", particularly Sr2+, are replaced With an alkali metal (e.g., Na+ or K") ion in the matrix. These substitutions are believed to effect charge compensation. The phosphors of this invention can be prepared in powder form or as a ceramic. Phosphor materials of this invention can also be grown as single crystals Which display desirable phosphorescence properties, including long persistence. The phosphors of this invention can be used in a variety of applications, e.g., in luminous paints, luminous plastics and for night vision devices and manufactures. The phos phors in ceramic form can be used for manufacture of phosphorescent jewelry and other ornaments or apparel. The phosphors may also be used in manufacture of infrared laser beam sensors. BRIEF DESCRIPTION OF THE FIGURES FIG. 1 is a spectrum of the after-glow of a pelleted sample of SrAl4O7(0.1B2O3):0.01Eu2",0.02Pr3+ measured at vary ing time (5 60 sec) after exposure of the sample to a 4 W UV lamp for two minutes. FIG. 2 is a graph of decay of the after-glow of (a) SrAl4O7(0.1B2O3):0.01 Eu2+,0.02Pr3+; and (b) of commer cial blue phosphor CaSrSzBi after exposure of the phosphors to a 13 W?uorescent lamp for 10 minutes. The threshold of eye sensitivity is indicated by a horizontal dashed line. FIG. 3 illustrates the excitation and emission spectra of SrAl4O7(0.1B2O3):0.01Eu2",0.02Pr3+ Where excitation Was monitored at 488 nm. FIG. 4 is the X-ray diffraction pattern of a sample of SrAl4O7(0.1B2O3):0.01 Eu2+,0.02Pr3+. FIG. 5 is a spectrum of the after-glow of a sample of SrAl4O7(0.1B2O3):0.01Eu2+,0.02Ho3+, measured at varying times (5 60 sec) after exposure of the sample to a 4 W UV lamp for two minutes. FIG. 6 is a graph of decay of the after-glow of (a) SrAl4O7(0.1B2O3):0.01 Eu2+,0.02Ho3+; (b) SrAl4O7 (0.1B2O3):0.01Eu2",0.02Pr3+ and (c) of commercial blue phosphor CaSrSzBi after exposure of the phosphors to a 13 W?uorescent lamp for 10 minutes. The threshold of eye sensitivity is indicated by a horizontal dashed line. FIG. 7 illustrates the excitation and emission spectra of SrAl4O7(0.1B2O3):0.1Eu2",0.02Ho3+ Where excitation Was monitored at 488 nm. FIG. 8 is a spectrum of the after-glow of a sample of SrAl4O7(0.1B2O3):0.01Eu2",0.02Nd3+ measured at varying 6,117, time (5 60 sec) after exposure of the sample to a 4 W UV lamp for two minutes. FIG. 9 is a graph of decay of the after-glow of (a) SrAl4O7(0.1B2O3):0.01 Eu2+,0.02Nd3+; (b) SrAl4O7 (0.1B2O3):0.01Eu2",0.02Pr3+ and (c) of commercial blue phosphor CaSrSzBi after exposure of the phosphors to a 13 W?uorescent lamp for 10 minutes. The threshold of eye sensitivity is indicated by a horizontal dashed line. FIG. 10 illustrates the excitation and emission spectra of SrAl4O7(0.1B2O3):0.01Eu2",0.02Nd3+ Where excitation Was monitored at 488 nm. FIG. 11 is a graph of decay curves of the after-glow of SrAl4O7(0.1B2O3):0.01Eu2",0.02R3+ measured in the?rst 15 sec. after exposure to a 13 W?uorescence lamp (measured at 488 nm). Decay curves for R=La (V), Ce (0), Sm (Q), Gd Tb (*), Dy (III), Er (A), Tm (0), Yb (x), and Lu (+) are shown. The decay curve of the sample SrAl4O7:Eu,Nd (O) is also shown for comparison. FIG. 12 is a graph comparing after-glow decay curves for samples of SrAl4O7(0.1B2O3):0.01Eu, 0.01Pr co-doped With 0.01 Y (x), Lu(V) or La(A). FIG. 13 illustrates the excitation and emission spectra monitored at 488 nm of SrAl4O7(0.1B2O3) activated With Eu and codoped With Pr and Y. FIG. 14 is a graph comparing after-glow decay curves of SrAl4O7(0.1B2O3) activated With Eu and codoped With either (a) Pr and Dy, (b) Ho and Dy or (c) doped only With Pr. The threshold of eye sensitivity is indicated by a hori Zontal dashed line. FIG. 15 illustrates the spectra of the after-glow of SrO_64BaO_33Al4O7:0.01Eu, 0.02Pr after exposure to a 4 W UV lamp for 2 minutes as a function of time after illumi nation (III, after 5 sec.; 0, after 20 sec. and A, after 60 sec.). FIG. 16 illustrates the spectra of the after-glow of SrO_49CaO_49Al4O7:0.01Eu, 0.02Pr after exposure to a 4 W UV lamp for 2 minutes as a function of time after illumi nation (III, after 5 sec.; 0, after 20 sec. and A, after 60 sec.). DETAILED DESCRIPTION OF THE INVENTION This invention relates to long-persistence blue phosphors. Phosphors of this invention are based on doping of an activator (an emitter) into a host matrix. Several basic physical factors should be considered in developing such phosphors. The host (or matrix) and activator are selected to provide the desired emission color (dependent upon the Wavelength of emission) and high quantum e?iciency. The energy of the localized ground state of the activator should be Well above the valence band of the host to allow persis tent phosphorescence to occur. Persistent phosphorescence Was discovered in the 11th century in China and Japan and in the 16th century in Europe (Shionoya, S. (1998) in Phosphor Handbook, Shionoya, S. and Yen, W. M. (eds.), CRC Press, Inc., Boca Raton, N.Y, p. 3). The phenomenon involves two kinds of active centers: emitters and traps. The phosphorescent dynamics are com plex and many aspects remain unclear. Thermoluminescence and photostimulable phosphorescence are physically gov erned by mechanisms similar to persistent phosphorescence Chen, R and McKeever, S. W. S. (1997), Theory of Ther moluminescence and Related Phenomena, World Scienti?c, Singapore; Sonoda, M. et al. (1983) Radiology 148:833). The main difference between these three phenomena appears to be the depth of traps. When a phosphor possesses centers With certain trapping depth Which can be effectively acti

RARE-EARTH DOPED PHOSPHATE GLASSES FOR NEODYMIUM LASER SYSTEMS POSSESSING A GREATLY ENHANCED PUMP POWER CONVERSION

Submit To: The American Ceramic Society, 12 Annual Meeting & Exposition April 3 May 3, 2, St. Louis, Missouri RARE-EARTH DOPED PHOSPHATE GLASSES FOR NEODYMIUM LASER SYSTEMS POSSESSING A GREATLY ENHANCED