Flame-excited luminescence in the oxides Ta2O5, Nb2O5, TiO2, ZnO, and SnO2

The flame-excited emission (candoluminescence) of the oxides Ta 2 O 5 , Nb 2 O 5 , TiO 2 , ZnO, and SnO 2 have been reexamined. By measuring the emission spectra as a function of temperature in comparison with the optical band gap, also measured as a function of temperature, it is concluded that a portion of the emission, particularly in Ta 2 O 5 and Nb 2 O 5 , is non-thermal. The results support the hypothesis that the excess emission is due to recombination of electron–hole pairs created by de-excitation of neutral radicals on the phosphor surface.