Evidence for the neutrality of luminescence centres in chalcogenide glasses

Abstract

New experimental results are reported which suggest that luminescence centres in chalcogenide glasses are not charged as is widely believed. Measurements of the photoluminescenee excitation quantum efficiency and the absence of any effect on the luminescence of intense magnetic or electric fields strongly suggest that the centres are neutral and that electron-hole pairs at such centres are tightly bound. A number of other recent experiments are reviewed which offer additional evidence for a dipole-centre model of luminescence. In this model, dipole centres (perhaps intimate valence-alternation centres) are excited by absorbed photons, some luminescence is emitted by the excited state in ∼ 10⁻⁸ s before it decays into a meta-stable state which lives for ∼ 10⁻⁴ s. During the latter time diffusion and energy transfer take place. The time and temperature dependence of photoluminescence fatigue is also reported. Since the temperature dependence of fatigue is so different from that of the luminescence, it is suggested that the two processes are independent.