Degradation mechanism of phosphors by vacuum ultraviolet excitation

The mechanism of luminance decrease of phosphors excited by a Xe plasma discharge has been studied. It is shown experimentally that the aging process is mainly due to the vacuum ultraviolet excitation (VUV). It is demonstrated that the degradation mechanism can be accelerated by using 193 nm laser excitation. Based on excitation, reflectance, thermoluminescence spectra and ageing or bleaching processes by laser excitation, the main causes of the degradation are demonstrated. The aging process can be separated in two different processes depending on the temperature: a first one, at low temperature, corresponding to the autoionisation of luminescent centers; and a second one, at high temperature, linked to the formation of traps in the phosphor. These traps induce a perturbation of the energy migration in the phosphor. The relevant parameters of the creation of traps are highlighted: density of the VUV excitation, temperature, atmosphere and pressure surrounding the phosphor.