Unusual heating rate dependence of thermoluminescence glow peaks of gas single crystals.

Characterization of defect centers existing in GaS single crystals were studied by virtue of thermoluminescence (TL) experiments accomplished in the temperature ranges of 10-230 K. Two distinctive peaks centered at peak maximum temperatures of 91 and 146 K and one faint peak, like a shoulder, appeared around 175 K were detected from the TL emission of the crystal by heating the sample with a rate of 1.0 K/s. Among the analysis methods well-known from the TL theory, curve fitting method was applied to calculate the activation energy of trap levels related to those of obtained peaks and the thermal activation energy values of 52, 200 and 304 meV were established, respectively. Heating rate dependence of the observed peaks was studied by successfully achieved measurements with various heating rates between 0.2 and 1.0 K/s (See Figure). The shifts of the TL peaks to higher temperatures were obtained with increasing heating rate. Interestingly, both anomalous and normal heating rate behaviors of the peaks were observed together. Clearly, the intensity of the peak A diminished with raising heating rate as expected. However, the intensity of the peak B increased seven fold with implementation of the highest heating rate. This conduct was interpreted with semi-localized transition model [1]. Existence of such two different behavior of the TL peaks was firstly experienced. Moreover, distribution of the trap levels were investigated by employing different illumination temperatures ranging from 10 to 30 K. This resulted with increase of the activation energies of the trap levels from 52 to 90 meV, from 200 to 268 meV and from 304 to 469 meV, respectively, which can be ascribed to a quasi-continuous distributio