On the luminescent behaviour of europium in yttrium oxide and yttrium vanadate hosts

Abstract

Europium-doped Y2O3 and YVO4 were excited by ultraviolet and 10 kV electrons to give the red emission of Eu3+. Increase in the fluorescence output with temperature under uv excitation results from an increased absorption and a more efficient energy transfer to the Eu3+ ions from charge-transfer states involving the Y-O and V-O componensts of the lattices. The absence of thermal quenching of fluorescence for (Y2O3∶Eu) is attributed to the high energy of its charge-transfer states which forbids the5D0 state to come into thermal contact with them. Complete quenching would occur above 2000 K as predicted from an estimated activation energy of 24 417 cm−1. Quenching of cathodoluminescence of (YVO4∶Eu) commences at 150 K due to the lower energy of its charge-transfer states. The experimentally-deduced temperature for complete quenching of cathodoluminescence for (YVO4∶Eu) is lower than that predicted from an estimated thermal activation energy of 14 217 cm−1; the difference being attributed to localized heating effects induced by electron bombardment. It is suggested that europium ions do not take part in thermoluminescence processes. Electron-hole recombinations occur at host sites to give the observed glow peaks which have been ascribed to traps produced by lattice defects and uncontrollable impurities in the undoped hosts.