Infrared luminescence, thermoluminescence and defect centres in Er and Yb co-doped ZnAl2O4 phosphor

Er and Yb co-doped ZnAl2O4 phosphors were prepared by solution combustion synthesis and the identification of Er and Yb were done by energy-dispersive X-ray analysis (EDX) studies. A luminescence at 1.5 mu m, due to the I-4(13/2) -> I-4(15/2) transition, has been studied in the NIR region in Er and Yb co-doped ZnAl2O4 phosphors upon 980 nm CW pumping. Er-doped ZnAl2O4 exhibits two thermally stimulated luminescence (TSL) peaks around 174A degrees C and 483A degrees C, while Yb co-doped ZnAl2O4 exhibits TSL peaks around 170A degrees C and 423A degrees C. Electron spin resonance (ESR) studies were carried out to identify defect centres responsible for TSL peaks observed in the phosphors. Room temperature ESR spectrum appears to be a superposition of two distinct centres. These centres are assigned to an O- ion and F+ centre. O- ion appears to correlate with the 174A degrees C TSL peak and F+ centre appears to relate with the high temperature TSL peak at 483A degrees C in ZnAl2O4:Er phosphor.