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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]

We discuss an approach by which the initial rise (IR) method can be extended to evaluate the frequency factor (s) of a glow peak, in addition to activation energy (E) that is usually obtainable from it. The approach requires that the phosphor be irradiated to a dose near or equal to the saturation dose of the glow peak to be analyzed. By plotting ln(I) against 1/T for the thermoluminescence glow peak, one obtains a straight line whose gradient is - E/k and intercept is ln(n0s/β) from which E and s are determined respectively. The approach was used to analyze two numerically generated glow peaks and reproduce with reasonably good accuracy the E and s values used to generate the glow peaks. It is also shown that when it becomes necessary to include intensities above 10% of the maximum glow peak intensity, the error introduced into the calculated frequency factor by the assumption n≅ n0 is always negligible when the analysis is done by plotting ln(I/n) against 1/T. In this case the frequency factor is obtained from ln(s/β) which is now the intercept. Two experimental glow peaks were also analyzed using the new IR method approach and peak shape method. Good agreement, which again shows the validity and reliability of the present approach was observed between the values of E and s obtained by the two methods. [ABSTRACT FROM AUTHOR]

We present a method for the estimation of defect (trap) physical parameters from thermoluminescence (TL) glow peaks. In this method, the order of kinetics b is determined using two values of TL intensity each of which corresponds to the same temperature ( T 1 ) on two separate glow peaks of a phosphor. The two glow peaks are obtained from two aliquots of the phosphor irradiated to same dose but read out at different heating rates. The proposed method requires a minimum of only two data points in contrast to standard peak shape (PS) methods that require three points corresponding to three different temperatures on the same glow peak. Once the order of kinetics b is determined, the activation energy E is calculated by taking a second point ( T 2 ) on any one of the two glow peaks. The values of b and E thus obtained are used to evaluate the frequency factor S ′′ and the number of trapped electrons before the heating begins n o . The validity of the method was checked using two numerically generated glow peaks. For the two cases, the method reproduced the input values reasonably well. The method was also used to analyse two experimental glow peaks. The results obtained provide a reasonably good fit to the experimental data. The kinetic parameters calculated using the present technique are comparable to those calculated using PS and initial rise methods. Initial guesses can easily be obtained for E and S ′′ using the present technique when a glow curve is to be deconvoluted with a model consisting of many unknown parameters with E and S ″ inclusive. [ABSTRACT FROM AUTHOR]

Polycrystalline CaTa2O6:Pr3+ phosphor is prepared by calcination of a stoichiometric mixture of Ta2O5 and CaCO3 plus a 0.5 mol% PrCl3 dopant level (1200 °C, 4 h). [ABSTRACT FROM AUTHOR]