Luminescent defects in nanostructured silica

Abstract

The spectral and kinetic properties of excited states of luminescent defects (oxygen-deficient centers) in SiO₂ ceramics are studied using pulsed cathodoluminescence and time-resolved photoluminescence. It is found that, in nanostructured samples prepared by thermal decomposition of polysilazane in air, there can exist modifications of oxygen-deficient centers in the form of surface analogs of either neutral oxygen monovacancies ≡Si-Si≡ (≡Ge-Ge≡) or twofold-coordinated silicon atoms =Si: (=Ge:). Photoluminescence of these centers is efficiently excited in the optical absorption bands of E′_s surface centers and silicon clusters ≡SiSiSi≡ and can be associated with the intercenter energy transfer in the course of their nonradiative relaxation. The photoluminescence and excitation spectra indicate thermally induced conversion of different types of oxygen-deficient centers. The specific features of the thermally induced changes in the luminescence characteristics of the defects due to the transformation of the structure of the silica samples from amorphous to partially crystalline are revealed from analyzing the spectral composition and decay kinetics of pulsed cathodoluminescence.