Thermal quenching properties of ultraviolet emitting centers in mesoporous silica

We report an investigation of the thermal quenching properties of the ultraviolet emission observed in mesoporous silica. The optical emission is due to the contribution of two emitting centers at 3.7 and 4.0 eV and previously assigned to strong- and weak-interacting silanols (Si-OH) located at the surface of the material. We investigate the temperature dependence of the lifetimes and the photoluminescence amplitudes of the two centers, in the 10-300 K range, by exciting in the ultraviolet and vacuum ultraviolet region with synchrotron radiation. The analysis of the lifetimes, carried out in the framework of a biexponential model at all the temperatures and excitations, and of the temperature dependence of the photoluminescence amplitude displayed different quenching properties in samples with different pore diameters. In addition, the thermal dependence of the photoluminescence amplitudes shows a distribution of the activation energy as a function of the emission energy in samples with smaller pore diameter.