TRANSIENT PHOTOLUMINESCENCE FROM HIGHLY DISORDERED SILICA-RICH NATURAL PHASES WITH AND WITHOUT NANOSTRUCTURES

Abstract

The ultrafast transient photoluminescence of impact silica-rich glasses and nanostructured opals is investigated at the (sub)nanosecond time scale. Spectral and temporal data were acquired with a high-resolution streak camera under high-density energy laser excitation at 4.17 eV (297 nm). All samples reveal blue photoluminescence relaxing in less than 50 ns. Relaxation decays and luminescence energy vary strongly from opals to impact glasses. Opals are found to relax in less than 16 ns with a maximum emission at 2.6-2.8 eV (443-477 nm) while the high-silica glasses exhibit a much longer luminescence in the 50-ns time window, which is spectrally blueshifted towards 3.0-3.5 eV (354-413 nm). Results are interpreted in terms of the presence of nonbridging oxygen atoms, network modifiers, and nanostructures which produce emission from self-trapped excitons and from excitons recombining at surface defects. The short-lived emissions of opals are characteristic of intrinsic surface photoluminescence quenched after about 10 ns via nonradiative decay channels with an annihilation component, and involve recombination luminescence of self-trapped excitons.