Photoluminescence in amorphous MgSiO_3 silicate

TL;DR

This study investigates how annealing amorphous MgSiO_3 silicate affects its photoluminescence, linking structural changes and defect formation to emission properties, with implications for understanding cosmic dust emissions.

Contribution

It provides laboratory evidence connecting structural reordering and defect formation in amorphous MgSiO_3 to its photoluminescence behavior, highlighting the role of non-bridging oxygen hole centres.

Findings

Photoluminescence peaks at ~450°C during annealing.

Photoluminescence is linked to non-bridging oxygen hole centres.

Crystallisation reduces and eventually eliminates photoluminescence.

Abstract

Samples of amorphous MgSiO_3 annealed at temperature steps leading up to their crystallisation temperature show a rise in photoluminescence activity, peaking at ~450C. The photoluminescence band has a main peak at 595nm and a weaker peak at 624nm. We present laboratory data to show that the maximum in photoluminescence activity is related to substantial structural reordering that occurs within a relatively narrow temperature range. We attribute the origin of the photoluminescence to non-bridging oxygen hole centre defects, which form around ordered nano-sized domain structures as a result of the breakup of tetrahedral connectivity in the disordered inter-domain network, aided by the loss of bonded OH. These defects are removed as crystallisation progresses, resulting in the decrease and eventual loss of photoluminescence. Thermally processed hydrogenated amorphous silicate grains could therefore represent a potential carrier of extended red emission.