Thermoluminescence and emission spectra of uv-grade Al2O3 from 90 to 500 K

Abstract

Thermoluminescence (TL) from uv‐dosimetry‐grade Al₂O₃ has been studied over the temperature range from 90 to 500 K. Two intense glow peaks are observed at 270 and 435 K as a result of uv irradiation. Thermal activation energies and frequency factors for the 270 and 435 K peaks were determined to be E=0.69 eV and s=3.5×10¹⁰ sec⁻¹; and E=1.11 eV and s=7.0×10¹⁰ sec⁻¹, respectively. The 270 and 435 K peaks yield identical emission spectra consisting of a broadband (FWHM=90 nm) with a maximum at 420 nm. Also, they both exhibit emission in the red region of the spectrum. Photobleaching experiments revealed that both glow peaks could be readily photobleached by irradiation with either 230 or 410‐nm radiation. The glow peak at 435 K is attributed to the thermal annealing of V⁻_OH centers (a hole trapped on an oxygen ion adjacent to a cation vacancy with an OH ion nearby), and it is suggested that the 270 K peak is possibly due to the thermal annealing of V⁰_OH centers (two holes trapped at adjacent oxygen ions next to a cation vacancy with an OH ion nearby). X irradiation produces two additional TL glow peaks at 210 and 385 K and a knee at 300 K. Thermal activation energies and frequency factors obtained for the 210 and 385 K glow peaks are E=0.47 eV and s=1.6×10⁹ sec⁻¹, and E=1.05 eV, s=3.6×10¹² sec⁻¹, respectively. Spectral distribution of the emission from these two peaks was identical, consisting of a broadband (FWHM=90 nm) that peaked at 310 nm. Two other types of Al₂O₃ crystals were investigated. One contained 0.05% chromium + 0.1% titanium by weight and yielded no TL upon uv or x irradiation. A sample containing 0.05% titanium by weight yielded a glow curve with peaks at 280 and 425 K. Trap parameters were determined to be E=0.77 eV and s=4.5×10¹¹ sec⁻¹, and E=1.06 eV and s=1.5×10¹² sec⁻¹, respectively. X irradiation produced additional glow peaks at 215 and 355 K and a knee at 265 K. The 215 K peak was the only additional peak sufficiently resolved to allow determination of activation energy (E=0.49 eV) and frequency factor (s=3.3×10¹⁰ sec⁻¹). The 280 K emission spectrum peaks at 500 nm (FWHM=135 nm) and also exhibits emission near 310 nm. Spectral distribution of the TL resulting from the 425 K peak indicated a band (FWHM=135 nm) with a maximum at 490 nm.