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Sr4Al14O25:Eu2+,Dy3+ is a commercially available green light emitting persistent luminescent phosphor. Owing to its complex crystalline structure and induced point defects, it shows fascinating luminescence that persists to typically up to 18 hrs after excitation. We report a trap-spectroscopic analysis of Sr4Al14O25:Eu2+,Dy3+ using thermoluminescence (TL). A TL glow curve measured at 1 °C/s following irradiation to 2 Gy at 20 °C shows two maxima at ~64 (labelled as P1) and 252 °C (P2). The variation of integrated TL intensity as a function of heating rate shows competition between radiative and non-radiative recombination processes. Beyond 1 °C/s heating rate, the non-radiative recombination process dominates and the luminescence efficiency drops sharply beyond 100 °C. The activation energy for thermal quenching is estimated to be W = 0.69 ± 0.07 eV. The peak maxima of P1 and P2 after correction for thermal quenching are found at ~70 and 275 °C. In addition, a secondary peak appears on the high temperature side of P1. Both the peaks show a gradual shift in their peak position Tm towards high temperature with preheating temperature Tstop. Moreover, the peaks also show a similar shift in Tm towards high temperature with increase in irradiation temperature Tirr. This suggests that peaks P1 and P2 are combinations of several closely spaced overlapping components. The activation energy of the component peaks comprising P1 is estimated to be ~0.63 - 0.68 eV whereas that of the component peaks comprising P2 is ~1.22 - 1.65 eV. An analysis of the fractional area between a pair of glow curves measured from the sample irradiated at different temperatures (Tirr) shows that the trap distribution associated with peak P1 is non-Gaussian whereas that associated with peak P2 follows Gaussian distribution. [ABSTRACT FROM AUTHOR]

Calcite, as do all carbonates, derives from the (CO3)2- anion. Calcite produces intense thermoluminescence (TL) which is mostly attributed to presence of Mn2+ anions. The emission spectra of calcite [1] and carbonatite [2] consist of broadband features at lower temperatures and line structures at high temperatures. These wavelength multiplexed differences are attributed to the solubility of Mn within calcite [1]. Although there has been considerable progress in understanding mechanisms of TL in calcite, corresponding advance related to optical stimulation has been halting. In this study we combine the utility of optical stimulation with the facility of thermal stimulation to study the phototransferred thermoluminescence (PTTL) of calcite induced by 470 nm blue-, 525 nm green- and 405 nm illumination. The conventional glow curve measured during heating to 600oC has an indeterminate number of glow peaks only three of which stand out and are regenerated under phototransfer. These are the ones studied. PTTL time-response profiles, that is, the dependence of PTTL intensity on the duration of illumination, are analysed using three methods, namely, a matrix- based analytical model, by use of vector fields and by theoretical modelling. We also address attendant effects such as backscattering to donor traps and competition effects, where supposed donor electron traps suppress electron trapping at acceptor electron traps. The time-response profiles corresponding to blue and UV light illumination displays the archetype increase through a maximum whereas that induced by green light is drawn out and, in some cases, tends to saturation. Surprisingly, the PTTL induced from deep electron traps by 405 nm illumination counterintuitively increases monotonically. We consider the extent to which this behaviour reflects the influence of slow bleaching components at the higher end of the corresponding PTTL peak or the effect of emission over a range of excited states as predicted by the modified Orgel (1955) diagram rather than the principle 4P(4T1g) relevant here. The intensity of PTTL induced from deep electron traps increases with temperature of illumination with an activation energy of thermal assistance of 0.052 ± 0.002 eV and decreases at elevated temperatures with an activation energy of thermal quenching of 0.75 ± 0.06 eV. The long term behaviour of the PTTL as studied by stability theory shows unstable critical points. The dosimetric characteristics of the latter including pre-dose effects are described. [ABSTRACT FROM AUTHOR]