Spectral green cathodoluminescence emission from surfaces of insulators with metal-hydroxyl bonds

Abstract

Optical measurements of microscale crystals suggest a new model for the luminescence centers associated with classic spectral cathodoluminescence emissions, which has implications for their material and photonic properties. In particular, manganese impurities in aluminosilicate lattices are commonly associated with ultraviolet and green (UV&G) spectral cathodoluminescence (CL) emissions peaked at circa 280–290nm and 550–570nm. These UV&G emissions from insulator solids, composed of different metals, increase with the presence of hydroxyl groups by water dissociation, or hydro-peroxide decomposition, under ionizing or UV radiation exposure. The UV&G bands are found to be associated with surfaces of insulator solids as electron beams affecting only the external surface region –microns deep– of the samples. Since massive ice (H2O at −10°C) shows CL without UV&G bands, the origin must lie within hydroxyl groups in the chamber of the environmental scanning electron microscope that couple to surface metals. The increase of UV&G signals in insulator solids, including hydrothermal feldspars, low crystalline silica or synthetic SiO2 among others is commonly observed in samples after energetic hydrous treatments, The proposed mechanism consists of a nonspecific reaction electron-beam + 2 (Metal-OH) > H2O + O + photons, that agrees with radiolytic models but not with ligand field theory. Knowledge of this process might be useful to evaluate geological samples for dosimetry or dating purposes employing luminescence techniques.