Green Afterglow of Undoped SrAl2O4

Undoped SrAl2O4 nanocrystals were obtained via solution combustion using urea as fuel. The afterglow properties of undoped SrAl2O4 were investigated. Green afterglow from undoped SrAl2O4 is visible to the human eye when the 325 nm irradiation of a helium–cadmium laser (13 mW) is ceased. The afterglow spectrum of undoped SrAl2O4 is peaked at about 520 nm. From the peak temperature (321 K) of the broad thermoluminescence glow curve, the trap depth of trap levels in undoped SrAl2O4 is estimated to be 0.642 eV using Urbach’s formula. Based on first-principles density functional calculations, the bandstructures and densities of states are derived for oxygen-deficient SrAl2O4 and strontium-deficient SrAl2O4, respectively. Our results demonstrate that the green afterglow of undoped SrAl2O4 originates from the midgap states introduced by oxygen and strontium vacancies. The observation of green afterglow from undoped SrAl2O4 helps in gaining new insight in exploring the afterglow mechanisms of SrAl2O4-based afterglow materials.

Three-Point Area Method for Thermoluminescence Glow Curve Analysis and Its Application to the Glow Peak of K2SrP2O7:Pr

A method has been proposed to evaluate the kinetic parameters, viz. activation energy ($E$) and order of kinetics ($b$) from a single or isolated thermoluminescence (TL) glow peak. Along with the area under the entire curve, this method uses a set of three arbitrary data points and calculates the partial area under the curve from each point to the endpoint. In this way, the entire information associated with the curve is used and the method is named as ‘Three-Point Area’ (TPA) method. We have applied it successfully on a number of theoretically simulated TL curves generated in One Trap One Recombination centre (OTOR) model and General-Order Kinetics (GOK) model under quasi-equilibrium approximations with linear heating scheme. The activation energies are found in good agreement with input values for both the models. For OTOR model, temperature average of order of kinetics is estimated to compare with the present result. Systematic analysis is carried out for estimation of errors inherent in the method in the purview of GOK model. A closer look on the results reveals that any set of three points, preferably chosen from the rising side of the curve, can yield activation energy and order of kinetics. The validity of the method to extract $E$ and $b$ from experimental glow curves is exemplified by considering experimental TL data reported in literature. Finally, a complete study starting from the synthesis of a new phosphor $\mathrm{K_2SrP_2O_7:Pr} $ and analysis of the recorded TL data to estimate $E$ and $b$ employing the TPA method has been reported.