Quenching of the photoluminescence of porous Vycor glass by oxygen and ammonia

Abstract

Photoluminescence observed on porous Vycor glass (PVG) degassed at high temperatures has been found to be quenched by both oxygen and ammonia. The quenching appears to arise from the formation of adsorption complexes between the quencher molecules and the PVG surface. Quenching by oxygen is composed of reversible and irreversible processes at room temperature, which can be attributed to photoformation of weak adsorption complexes and (O^– ₂)_s anion radicals, respectively. The irreversible quenching found with ammonia is associated with the strong adsorption of ammonia on Lewis acid sites. From these results, together with those for absorption by PVG, the nature of the sites responsible for the emission and absorption of light energy has been discussed. In the case of oxygen, it has been suggested that trapping of photoformed electrons by oxygen may be operating to increase the probability of non-radiative processes.