Cathodoluminescence spectra recorded from surfaces of solids with hydrous molecules

Highlights: • Hydroxyl groups are universally present in solid samples kept in environmental conditions being potentially active luminescence emitters. • Cathodoluminescence spectra of very different sixty hydrous solid materials exhibit constant peaks at 315 nm and 620 and 650 nm. • Iron bearing materials, such as biotite, olivine or native iron (Fe 100%) show appreciable cathodoluminescence spectral bands. • Hydroxyl groups (315 nm) and water molecules (620 and 650 nm) are precursors of non-bridging oxygen hole centers. • These relationships between CL emissions and hydrous defects are important uses using luminescence techniques. - Abstract: Modern cathodoluminescence detectors coupled to Environmental Scanning Electron Microscopes (ESEM) with X-ray microanalysis are increasingly sensitive and, nowadays, low intense luminescence spectra may be recorded from nominally non-luminescent solid materials. Structural or attached hydroxyl groups are universally present in solid samples kept in environmental conditions being potentially active luminescence emitters. Hence, we collected cathodoluminescence (CL) spectra of sixty solid materials of minerals and synthetic compounds, organics and inorganics, metallic and non-metallic, crystalline and amorphous, including widespread CL bands at circa 315 nm and 620 and 650 nm from surfaces of solids with hydroxyl and hydrous molecules. We observed as iron bearing materials, such as biotite, olivine or native iron, show appreciable cathodoluminescence spectral bands associated with hydroxyl groups (315 nm) and water molecules (620 and 650 nm), being probable precursors of non-bridging oxygen hole centers. The wide set of very different samples analyzed shows spectral similarities among separated sample types but with the only common factor of the hydrous molecules. These conclusions seem crucial for remote sensing detection of water; environmental dosimetry; degradation of phosphor materials, etc. Analyzing spectral luminescence emissions of hydrated materials it is frequent to observe erroneous interpretations of their defect-emission relationships which should be avoided.