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

The flame-excited emission (candoluminescence) of the oxides Ta2O5, Nb2O5, TiO2, ZnO, and SnO2 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 Ta2O5 and Nb2O5, 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.