Optical, spectral and thermal properties of natural pumice glass

Pumice is a natural Si-rich material displaying a complex cathodo- (CL) and thermoluminescence (TL) glow curves. The UV-IR CL emission consists of (i) a UV waveband in the range of 340-420 nm,(ii) blue band at 450-480 nm and (iii) a broad emission in the green-red region (at 550-650 nm) that could be respectively linked to Non Bridging Oxygen Hole Centers (Si-O
- ), self-trapped excitons and point defects (Mn2+ −0.03%- and Fe −1.15%-). Thermal treatments performed on the TL glow curves allowed us to determine that the trap system could be associated with a continuum in the trap distribution, since successive thermal pretreatments in the range of 200-310 °C induce an emission that shifts linearly to higher temperatures when the thermal pretreatment (Tstop) is increased, while the intensity of the maxima decreases similarly to the peak area. The evaluation of the Ea values, s value and the trap system calculated by VHR, IR and Glow curve fitting methods considering three possible distribution function for n(E): gaussian, exponential and uniform, has given matching values for the 280 °C TL peak.