Growth and properties of LuAP:Ce with complex and simple substitutions

Transcription

1 Growth and properties of LuAP:Ce with complex and simple substitutions A.G.Petrosyan, M.Derdzyan, C.Pedrini, P.Lecoq, I.Kamenskikh, C.Dujardin, K.Ovanesyan

2 Institutions (a) Institute for Physical Research, Laboratory of Crystal Growth of Luminescent Materials, Ashtarak-2, , Armenia (b) Université de Lyon, Lyon, F-69003, France ; université Lyon 1, Villeurbanne, F-69622, France ; CNRS, UMR5620, Laboratoire de Physico-Chimie des Matériaux Luminescents, Villeurbanne, F-69622, France. (c) CERN, Division EP, CH-1211 Geneve 23, Switzerland (d) M.V.Lomonosov Moscow State University, Physics Department, Synchrotron Radiation Laboratory, Moscow, Russia Crystal Clear Collaboration

3 Contents Introduction Residual absorption in LuAP:Ce LuAP:Ce, Hf LuAP:Ca & LuAP:Hf LuAP:Ce, Sc Conclusions

4 The phase diagram of the Lu2O3-Al2O3 system T, С L + Lu 2 O 3 2:1 + Lu 2 O 3 L+ 2:1 2:1 + 3:5 ss 2:1 + 1:1 L + 3:5 ss 1:1 + 3:5 ss L+ 3:5 3:5 ss L + α-al 2 O Lu 2 O 3 + 3:5 ss 2:1 + 3:5 ss 3:5 + α-al 2 O 3 Lu 2 O Al 2 O 3 mol. % Al 2 O 3 J. Crystal Growth 2006

5 Vertical Bridgman Bridgman LuAP:Ce (18 * mm) or (13 * mm)

6 Spectral properties of Bridgman LuAP:Ce Transmission at λ=600 nm : 82% Transmission at λ=350 nm : 79%; Absorption coefficient at 260 nm : 1,5-6 см-1; Slope of the optical edge : 7,4-7.8 %/nm. Light yield ratio, 2*2*8mm elements (vertical/horizontal): 65-70%. Transmission, % LuAP:Ce Ce ~ 0,3% Transmission at 365nm in between 78%-80% Slope=7,4 %/nm λ, nm

7 Non-isovalent substitutions Ca2+, Hf4+, Zr4+, Ta5+, Th4+, Si4+ LuAP, LuYAP(Lu*70%) pure and Ce-doped Amounts: ppm Lu-site occupancy: Ca2+, Th4+, Zr4+, Hf4+ Al-site occupancy: Si4+, Ta5+

8 LuAP:Ce; LuAP:Ce,Hf (or Zr) Absorption coefficient (cm -1 ) ,3 cm -1 LuAP:Ce, Hf (30 ppm) LuAP:Ce Absorption coefficient at 260 nm (cm -1 ) 18 LuAP:Ce LuAP:Ce (super pure) 16 LuAP;Ce (low purity) LuAP:Ce, Hf (30 ppm) 14 LuAP:Ce, Hf (60 ppm) 12 LuAP:Ce, Zr (60 ppm) Ce (at.%) 0 1,4 cm λ (nm) T, % nm 20 a Nucl.Instr.& Meth., λ, nm

9 LuAP with non-isovalent substitutions Absorption coefficient (cm -1 ) nm 275 nm Absorption coefficient, cm LuAlO 3, Ca (20 ppm) LuAlO 3 Dif. abs. coef., cm nm 275 nm λ, nm λ (nm) Ca2+ ions increase absorption at 220 nm and 275 nm; Hf4+ ions produce the opposite effect. F-type centers responsible for absorptions at 220 and 275 nm Absorption coefficient, cm LuAlO 3,Hf (40 ppm) LuAlO nm 275 nm ΔK, cm -1 λ, nm λ, nm λ, nm

10 Positive role of Hf (or Zr, Ta, Si, Th) co-dopants 1. The concentration of oxygen vacancies can be decreased; absorption coefficient at 260 nm can be controlled 2. The intensity of the red luminescence at 600 nm is lower(measurements by I.Kamenskikh, 2007) 3. The decay time of the slow component is shorter by ns (CERN measurements 2006) No big influence upon the light yield so far observed (Lyon &CERN measurements)

11 Evident problems in LuAP:Ce Still high reabsorption, which increases with %Ce. Insufficient Ce concentration; no clear saturation of the light yield with Ce concentration; max achieved %Ce=0.5%

12 Ce distribution coefficient Size mismatch between Lu3+ (0.97 A) and Ce3+ (1.13 A) k= 0.17 Difficulty in isomorphous substitution of more than 0.4%. The doping process tends to distort the perovskite lattice of LuAP. High Ce gradients over the crystal length Means are required to incorporate Ce in an equilibrium manner

13 Possible ways Increase the unit cell volume Earlier tested examples - LuYAP and LuGdAP. Addition of a tripositive ion which is smaller than Lu3+ for volumetric size compensation

14 M.Kestigian and W.Holloway, 1968 (Sperry Rand) YAG: Nd, Lu The average radius of Nd3+ and Lu3+ is equal to that of Y3+. The lattice parameter must be the same as for YAG. Suggested mechanism volumetric size compensation. Result: incorporation of higher concentrations of Nd in optical quality YAG. Later studies : Lu3+ goes to Al3+ sites increasing the unit cell volume. M.Weber, R. Monchamp, et al, 1970 R. Monchamp, 1971

15 Isovalent substitution by Sc Ce 3+ r =1.14 Å Sc 3+ r =0.87Å ½ [r(ce)+r(sc)] = r(lu) Lu 3+ r =0.97Å Al 3+ r =0.53Å O 2- r = 1.40Å

16 Unit cell volume versus %Ce and Ce distribution in LuAP:Ce and LuAP:Ce,Sc V, A LuAP:Ce LuAP:Ce, Sc Ce concentration, at.% LuAP-Ce 0,5 at.%, Sc 0,5 at.% LuAP-Ce 0,5 at.% k = 0,3 k = 0, Ce, at.% g In LuAP:Ce,Sc, the distribution coefficient of Ce is almost twice larger

17 Conclusions 1. Additional impurities can be incorporated into the LuAP lattice to monitor the concentration of oxygen vacancies or the crystallographic structure. 2. Tetravalent ions suppress the oxygen vacancies and provide for LuAP:Ce crystals with low concentration of F-centers and low residual absorption at 260 nm 3. Volumetric size compensation mechanism is realized by simultaneous incorporation of Ce and Sc into the LuAP lattice. In LuAP:Ce,Sc the Ce3+ ions are incorporated into the lattice in an equilibrium manner. 4. It is expected that crystals with higher Ce concentration (over 0.5%) and less distortions of the lattice can be grown.

18 Acknowledgments This work was supported by : ISTC (Project # 1165), Armenian Ministry of Education and Science (Project # 0052) It was performed under the auspices of the Crystal Clear Collaboration.