LA3+ AND LU3+ ISOELECTRONIC CENTERS IN YAG

Roentgenoluminescence from Y3-xLaxAl5O12 (0 < x < 0.013) (YAG:La) and Y3-xLuxAl5O12 (0 < x < 3) (YAG:Lu) crystals grown by horizontal direct ional crystallization was investigated in the spectral range 200-400 n m between 80 and 500 K. The roentgenoluminescence spectrum of YAG:La e xhibits a broad band around 273 nm, assigned to La-Y isoelectronic cen ters formed upon substitution of La3+ for Y3+ in dodecahedral sites of the garnet structure. During heating of YAG:La crystals x-irradiated at 80 K, we observed thermoluminescence due to the recombination of de trapped electrons with holes at La sites, In contrast to intrinsic emi ssion (broad bands peaked at 265 and 295 nm) strongly quenched at 300 K, temperature quenching of the Lay band starts above 300 K. According ly, La doping causes a sharp increase in the intensity of UV luminesce nce at 300 K (by a factor of similar to 10 at x = 0.013). In contrast to La, the Lu dopant has virtually no effect on the spectral and tempe rature characteristics of the intrinsic UV emission because of the alm ost identical properties of the Y3+ and Lu3+ ions.