Photoluminescence in amorphous MgSiO3 silicate

Samples of amorphous MgSiO3 annealed at temperature steps leading up to their crystallization temperature show a rise in photoluminescence activity, peaking at similar to 450 degrees C. The photoluminescence band has a main peak at 595 nm and a weaker peak at 624 nm. 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 nanosized 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 crystallization 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.