Photoluminescent processes in K(1-x)Li(x)TaO3

A study of blue-green photoluminescence of K1-xLixTaO3 single crystals, und er UV irradiation, was performed in the range 15-120 K. It was shown that t he 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 d ecreases abruptly with an Arrhenius-like behaviour controlled by an activat ion energy of 70-100 meV. After low temperature excitation, a thermolumines cence spectrally very similar to PL and giving rise to a glow peak around 3 0 K is also observed. Correlations with recent results on photoconductivity and thermally stimulated currents are illustrated. An argument in favour o f close-pair recombinations between Ta4+ and O- centres is proposed.