Photoluminescent processes in K1-xLixTaO3

A study of blue-green photoluminescence of K1-xLixTaO3 single crystals, under UV irradiation, was performed in the range 15-120 K. It was shown that the emission is strongly enhanced and thermally more stable with respect to pure KTaO3, up to similar to 40 K. Above this point the yield of emission decreases abruptly with an Arrhenius-like behaviour controlled by an activation energy of 70-100 meV. After low temperature excitation, a thermoluminescence spectrally very similar to PL and giving rise to a glow peak around 30 K is also observed. Correlations with recent results on photoconductivity and thermally stimulated currents are illustrated. An argument in favour of close-pair recombinations between Ta4+ and O- centres is proposed.