LUMINESCENCE OF CALCIUM ORTHOPHOSPHATES ACTIVATED WITH DIVALENT EUROPIUM

Transcription

1 _._--- R672 Philips Res. Reps 23, ,1968 LUMINESCENCE OF CALCIUM ORTHOPHOSPHATES ACTIVATED WITH DIVALENT EUROPIUM by W. L. WANMAKER and J. W. er VRUGT Absrac The phosphor a-ca3(p04)z-eu2+ shows under ulraviole exciaion a broad emission band wih a peak a 480 nm; in he {3 phase his peak is siuaed a 415 nm. The phosphor Ca.sMg.S(P04)z-Eu2+ has is emission maximum a 460 nm, a quanum efficiency for nm exciaion of abou 50 per cen and an energy-conversion efficiency for cahode-ray (20 kv) exciaion of 6 per cen. 1. Inrodueion Recenly a number of papers were published concerning he luminescence of alkaline-earh phosphaes acivaed wih divalen europium. Nazarova 1) described he cahodoluminescence of Sr(p03h-Eu, Sr3(P0 4 keu, Sr2P20rEu and a-ca2p20 7 -Eu. The phooluminescence of SrMgz(P0 4 )z-eu,mn and Mg3(P0 4 keu,mn was repored by Gorbacheva 2). The presen auhors described he luminescence of alkaline-earh pyrophosphaes acivaed wih divalen europium 3). In his paper we repor on he luminescence of calcium orhophosphaes acivaed wih divalen europium. 2. Experimenal The phosphors were prepared as described previously 3) from he following luminescen-grade saring maerials: CaHP04, CaCO;, BaC03, MgNH4P04, MgC03 and EU203' The puriy of EU203 was 99 9 per cen (as supplied by he firm Péchiney-Sain Gobain). The exciaion specra, diffuse-reflecion specra, emission specra and he efficiencies for ulraviole and cahode-ray exciaion were measured by a procedure described earlier 4,5). 3. Resuls and discussion 3.1. Ca3(P04)2.The compound Ca3(P04)2 is dimorphous: he a-ca3(p04h phase is sable a emperaures higher han 1180 C and he f3 phase is sable below his emperaure 6). I may be seen from fig. 1 ha he a-phase phosphor acivaed wih divalen europium shows a broad emission band (A mbx = 480 nm). The,B-phase phos-

2 LUMINEScENCE OF Ca ORTHOPHOSPHATES ACTIVATED WITH Eu Relaive inensiy J..(nm) Fig. 1. Specral-energy disribuion of he emission of X-Ca3(P04h-O'02 Eu2+ (curve 1) and of P-Ca3(P04h-O'02 Eu 2 + (curve 2). Mainly 254-nm exciaion. l00i r---~ ~------~----.Reflecion (r) (%) Rel. quanum oupu (q)(%) 50'r---~~ ~~~----~~ J..(nm} Fig. 2. Diffuse-reflecion specra and exciaion specra of he luminescence of X-Ca3(P04h- 0'02 Eu2+ (curves 1) and of,b-ca3(p04h-0'02 Eu 2 + (curves 2). Relaive inensiy \. / --" OLL~~----~500~----~~~----~nmd -.À (nm) Fig. 3. Specral-energy disribuion ofhe emission of P-Ca3(P04h-O'02 Eu,0'10 Mn (curve 1) and of Cal.sMgl.S(P04h-O 02 Eu,0'10 Mn (curve 2). Mainly 254-nm exciaion.

3 364 W. L. WANMAKER and J. W. er VRUGT phor shows (in addiion o weak red emission lines, due o unreduced Eu3+) an emission band a 415 nm. In an invesigaion of in-acivaed calcium orhophosphaes we found ha magnesium raises he ransiion emperaure of Ca3(P04)z and barium lowers i 7). The same effec was observed wih Ca3(P04)z-Eu2+. Up o an amoun of 0 12 gramaom Eu per mole of Ca3(P04)z no effec of he Eu concenraion on he ransiion emperaure could be observed. The concenraion quenching in he ex phase sars wih abou 0 08 gramaom Eu per mole of Ca3(P04)2 and in he P phase wih abou 0 04 gramaom. These resuls arein accordance wih Blasse's heory haconcenraion quenching sars a a lower acivaor concenraion if he overlap of he exciaion and emission bands increases 8). I follows from figs 1 and 2 ha he overlap of he emission band band of he p-phase phosphor wih is exciaion band is higher han for he ex phase. When Eu and Mn are added simulaneously a Mn2+-emission band appears, in addiion o he Eu 2 + emission. Figure 3 shows ha in p-caip04)z-eu,mn he second band is locaed a 650 nm, he same wavelengh as found in his hos laice wih Sn 9), Ce 10) and Cu 11) as a sensiizer ion. Table I shows he efficiencies a room emperaure of he Eu2+ emission of our phosphors, boh for ulraviole exciaion and for exciaion wih cahode rays. I may be seen from his able ha he quanum efficiency of he ex phase of Ca3(P04)2-Eu2+ is higher han ha of he p-phase phosphor. As he preparaion condiions of he phosphors were no opimized he daa can give only a general impression of he efficiencies of hese ypes of phosphors. TABLE Efficiencies of Eu2+-acivaed calcium orhophosphaes; 1]CR = energy-conversion efficiency (%) for cahode-ray (20 kv) exciaion I phosphor quanum efficiency (%) cahode nm max. value ray exciaion in u.v. 1]CR region ex-ca2 96(P04)z-0 02Eu P-Ca2' 96(PO4h-0 02Eu Ca1 50Mg1'46(P04)z-0 02Eu Figure 4 shows he relaive brighness of ex- and p-ca3(p04)2-eu2+ as a funcion of emperaure, boh phosphors showing a srong decrease in brigh-

4 LUMINESCENCE OF Ca ORTHOPHOSPHATES ACTIVATED WITH Eu ness when heaed above room emperaure. OO Relaive brighness 50.~ ", "..., ''',... <, 1\ -., \ y '-',3..., '- <, r- --- " _ Temperaure (oe) Fig, 4. Variaion of brighness wih emperaure of Eu 2 + -acivaed calcium orhophosphaes. Mainly 254-nm exciaion. ' curve 1 phosphor a-ca3(p04h-o'02 Eu 2 P-Ca3(P04h-O'02 Eu 3 Cal.sMgl.S(P04h-O 02 Eu 3.2. Ca1'SMg1'S(P04)2 In he sysem Ca3(P04h-Mg3(P04h only one compound exiss wih wo caions, viz. Ca1.sMg1'S(P04)212). Acivaion of Mg3(P04h wih divalen europium resuls in phosphors of low brighness, bu Ca1.sMg1'S(P04)2-Eu2+ is an efficien phosphor, since a quanum efficiency of 52 per cen wih nm exciaion was measured (able 1). The efficiency wih cahode-ray exciaion is high as compared wih oher Eu2+-acivaed phosphors 3.13). Reflecion (r) (Ye) Rel. quanum oupu ~OO oor---,:::::>"'<~-,----,... -,;-----r---,1oo jl ~----\---1 -l50 I \ (r) Relaive inensiy ~~00~---300~-----L4~ ~00~----~600~~0 -.À (nm) Fig. 5. Diffuse-reflecion specrum, exciaion specrum of he luminescence and specralenergy disribuion of he emission (254-nm exciaion) of Cal.sMg1.S(P04h-O 02 Eu2+. The emission peak ofhis phosphor is siuaed a nm (fig. 5). In some cases he peak was found a 440 nm and one sample showed an emission wih a fla maximum a nm. This may indicae he presence of more han

5 366 W. L. WANMAKER and J. W. er VRUGT one acivaor sie, a phenomenon also found wih in-acivaed calcium orhophosphaes 7). As he absorpion of he hos laice Cal.sMgl'S(P04h a a wavelengh of nm is only abou 30 per cen, he absorpion of he exciing radiaion of he phosphor in his, region akes place in he Eu2+ ions: 4f7 -+4f 6 5d. The brighness a elevaed emperaures of Cal.sMgl'S(P04)2-Eu2+ is higher han hose of 0:- and!j-ca3(p04)2-eu2+, as may be seen from fig. 4. Wih manganese as a coacivaor a Mn emission band appears a 630 nm (fig. 3). Acknowledgemen The auhors wish o express heir hanks o Mr J. G. Verlijsdonk and Mr G. J. R. A. Tops for preparing he phosphors and measuring he emperaure dependence of he phosphors; o Mr C. Bakker for measuring he reflecion and exciaion specra and o Dr A. Bril for measuring he efficiencies of he phosphors. Eindhoven, 24h April 1968 REFERENCES 1) V. P. Nazarova, Bull. Acad. Sci. USSR, Phys. Ser. 25, 323, ) N. A. Gorbacheva, Jzves. Akad. Nauk SSSR, Phys. Ser. 30, 1521, ) W. L. Wanmaker and J. W. er Vrug, Philips Res. Reps 22, 355, ) A. Bril and W. L. Wanrnaker, J. elecrochem. Soc. 111, 1363, ) A. Bril and H. A. Klasens, Philips Res. Reps 7, 401, ) G. Trömel and H. Möller, Z. anorg. allg. Chemie 206, 239, ) W. L. Wanmaker and D. Radielovi é, Elecrochem. Technology 2, 16, ) G. Blasse, Philips Res. Reps 23, , ) K. H. Buler, J. elecrochem. Soc. 100, 250, ) H. C. Froelich and J. M. Margolis, J. elecrochem. Soc. 98, 400, ) W. L. Wanmaker and C. Bakker, J. elecrochem. Soc. 106, 1027, ) J. Ando, Bull. chem. Soc. Japan 31, 201, ) G. Blasse, W. L. Wanrnaker, J. W. er Vrug and A. Bril, Philips Res. Reps 23, 189, 1968.