Identification of defect centers responsible for thermoluminescence emission in sol-gel synthesized calcium silicate phosphor.

The thermoluminescence (TL) of calcium silicate phosphor (CSO) prepared by the sol-gel method and sintered at 1200 °C were investigated. From Tm-Tstop curve, TL emission spectrum and computer deconvolution using electron traps with discrete and continuous distributions, the glow curves were found to be composed of four TL peaks (117, 190, 250 and 275 °C) with a single emission band centered at 370 nm. Electron paramagnetic resonance (EPR) investigation has been carried out to identify the defect centers formed in the CSO phosphor by γ-irradiation and find the centers related to the TL process in the phosphor. At room temperature, three defect centers were observed. The first center, characterized by the principal g-values of 2.014, 2.011, and 2.0080 was assigned to an O- ion. The second center with g-values 2.015, 2.013, and 2.010 is also attributed to an O- ion and is associated with the TL peak at 280 °C. The third center, with an isotropic g-value of 2.0011 was identified as the F+ center (singly ionized oxygen vacancy) and relates to the TL peak at 280 °C.

Identification of ESR centers and their role in the TL of natural salt from Lluta, Peru.

In this study, the thermoluminescence (TL) properties of natural NaCl from Lluta, Arequipa-Peru was investigated. The number of peaks and the kinetic parameters associated with the TL glow peaks of NaCl sample after gamma-irradiation were analyzed by initial rise and deconvolution method. Defect centers induced in pure salt by gamma irradiation have been studied by electron spin resonance (ESR) with a view to identify the centers associated with the TL process in the salt. Thermal annealing experiments indicate the presence of three defect centers. Center I characterized by the g-value 2.011 is identified as an O- ion and relates with the dominant TL peak at 220 °C. Center II with a g-value of 2.0058 is attributed to a F center and is found to correlate with the 128 °C TL peak. Center III has of g-value 2.014 and is also assigned to an O- ion.

Radiation dosimetry using decreasing TL intensity in a few variety of silicate crystals.

This study shows that there are some ionic crystals which after irradiation with high gamma dose Dm and subsequent irradiation with low doses ranging up to 500Gy present a decreasing TL intensity as dose increases. This interesting feature can be used as a calibration curve in radiation dosimetry. Such behavior can be found in green quartz, three varieties of beryl and pink tourmaline. In all these silicate crystals it can be shown that irradiation with increasing γ-dose there is a dose Dm for which the TL intensity is maximum. Of course, Dm varies depending on the crystal and irradiated crystal with the dose Dm is stable. If one of these crystals is taken and irradiated with doses from low values up to 400-500Gy, a curve of decreasing TL intensity is obtained; such a curve can be used as a calibration curve.

Study of luminescence, color and paramagnetic centers properties of albite.

A sample of natural albite, NaAlSi3O8, from the state of Minas Gerais, Brazil, has been investigated. The mineral is a solid solution of K-feldspar (4600 ppm--K) and Ca-feldspar (1100 ppm--Ca). The TL spectra of natural and the pre-annealed at high temperature albite presented a very intense band around 275 nm and weaker bands around 400 and 560 nm. Other TL properties have been investigated through monochromatic (275 nm and 400 nm) glow curves. The EPR spectrum measured at low temperature (77K) shows the typical 11 lines signal due to Al-O(-)-Al center superposed on Fe(3+) signal around g=2.0. The EPR spectra above 260 K show only g=2.0 signal due to Fe(3+) ions.