S. Dorendrajit Singh

Lifetime and quantum yield studies of Dy3+ doped GdVO4 nanoparticles: Concentration and annealing effect

GdVO4 nanoparticles doped with Dy3+ have been prepared using urea hydrolysis method in ethylene glycol medium. Linear decrease in the unit cell volume indicates the quantitative substitution of Gd3+ lattice sites by Dy3+ in GdVO4. The luminescence intensity of electric dipole transition at 573 nm is more than that of magnetic dipole transition at 483 nm. This has been attributed to the asymmetric environment of Dy3+ ion in GdVO4. Luminescence intensity decreases with increasing Dy3+ concentrations due to concentration quenching. This is supported by lifetime decay studies. There is no particle size effect on the peak positions of Dy3+ emission. There is an increase in the decay lifetime for F49/2 level with increase in heat treatment from 500 to 900 °C. This is attributed to the reduction in nonradiative process arose from surface inhomogeneities. The decay lifetime data follow the biexponential to monoexponential nature with increase of Dy3+ concentrations. There is an increase in the quantum yield with ...

Re-dispersion and film formation of GdVO4 : Ln3+ (Ln3+ = Dy3+, Eu3+, Sm3+, Tm3+) nanoparticles: particle size and luminescence studies

GdVO(4) : Ln(3+) (Ln(3+) = Dy(3+), Eu(3+), Sm(3+), Tm(3+)) nanoparticles are prepared by a simple chemical route at 140 °C. The crystallite size can be tuned by varying the pH of the reaction medium. Interestingly, the crystallite size is found to increase significantly when pH increases from 6 to 12. This is related to slower nucleation of the GdVO(4) formation with increase of VO(4)(3-) present in solution. The luminescence study shows an efficient energy transfer from vanadate absorption of GdVO(4) to Ln(3+) and thereby enhanced emissions are obtained. A possible reaction mechanism at different pH values is suggested in this study. As-prepared samples are well dispersed in ethanol, methanol and water, and can be incorporated into polymer films. Luminescence and its decay lifetime studies confirm the decrease in non-radiative transition probability with the increase of heat treatment temperature. Re-dispersed particles will be useful in potential applications of life science and the film will be useful in display devices.

Luminescence study of Eu3+ doped GdVO4 nanoparticles: Concentration, particle size, and core/shell effects

Nanoparticles of GdVO4 doped with Eu3+ and core/shell of GdVO4:Eu3+/GdVO4 are prepared by urea hydrolysis method using ethylene glycol as capping agent as well as reaction medium at 130 °C. Unit cell volume increases when GdVO4 is doped with Eu3+ indicating the substitution of Gd3+ lattice sites by Eu3+. From luminescence study, it is confirmed that there is no particle size effect on emission positions of Eu3+. Optimum luminescence intensity is found to be in 5–10 at. % Eu3+. Above these concentrations, luminescence intensity decreases due to concentration quenching effect. There is an enhancement in luminescence intensity of core/shell nanoparticles. This has been attributed to the reduction in surface inhomogenities of Eu3+ surroundings by bonding to GdVO4 shell. The lifetime for D50 level increases with annealing and core/shell formation.

Computerized glow curve deconvolution: the case of LiF TLD-100

It has been accepted by a large number of workers that the glow curve of LiF TLD-100 can be described by thermoluminescence (TL) peaks following the Randall-Wilkins (RW) equation, even though the model fails to explain a number of experimental facts. A further simplification of the model is the Podgorsak-Moran-Cameron (PMC) approximation which is also in use. This paper points out the limitation of the PMC approximation in deconvoluting glow curves of LiF TLD-100.

Particle size effect on TL emission of ZnS nanoparticles and determination of its kinetic parameters

Nanoparticles have large surface area, and most of the ions are lying on its surface. Could these surface ions be contributed in thermoluminescence emission or enhanced nonradiative transition? In view of this, we have prepared small sizes of ZnS nanoparticles at low temperature and made two samples, one as-prepared (size ∼3 nm) and the other heat-treated at 1073 K (size ∼32 nm). Characterization of the samples shows that the prepared phosphors are pure. Thermoluminescence (TL) glow curves could not be recorded in both samples without irradiation. Even for higher dose of γ-radiation the as-prepared samples could not show TL signal, but 1073 K heat-treated sample shows the TL signal. This may be due to the fact that smaller particles have large surface area compared to bigger particles, the surface ions may produce the nonradiative transitions. The kinetic parameters of the TL glow curves are evaluated by the conventional methods and compared with curve fitting computerised glow curve deconvolution (CGCD) technique. The variations in both techniques are found only ±0.02. The shape factor of all the glow curves ∼0.48, and these TL glow curves could be fitted with order of kinetics 1.5.

The determination of the trapping parameters of a thermoluminescence peak by using the Kirsh method

In this paper we analyse the suitability of a method proposed by Kirsh for the determination of the trapping parameters, namely the order of kinetics, activation energy and frequency factor, of a thermoluminescence (TL) peak by applying it both to numerically generated TL peaks and to an experimental TL peak of NaCl:I irradiated with 2.04 kGy of -rays. It is found that the method can be used irrespective of the order of kinetics. It is also shown that the method proposed by Rasheedy ( 8 (1996) 1291 and 29 (1996) 1340) is a special case of the Kirsh method.

Evaluation of temperature integral for temperature dependent frequency factors

The general method of evaluating the temperature integral for temperature dependent frequency factors have been considered. The values of the temperature integral as evaluated by the present method are in excellent agreement with those obtained numerically.ZusammenfassungEs wurde eine allgemeine Methode zur Auswertung des Temperaturintegrales für temperaturabhängige Frequenzfaktoren betrachtet. Die Werte für die Temperaturintegrale nach vorliegender Methode stehen in ausgezeichneter Übereinstimmung mit den numerisch erhaltenen Werten.

Thermoluminescence glow curve of gamma -irradiated calcite

The trapping parameters, namely the activation energy E, frequency factor s and b order of kinetics of the thermoluminescence (TL) peaks of calcites (brown and colourless varieties) irradiated with 4.08 kGy of gamma -rays, are determined using the least-squares curve-fitting technique. The electron lifetime tau of the peaks of calcite are calculated in order to estimate the upper limit of their utility in TL dating.

Low-temperature synthesis and particle size effect on photoluminescence of YVO4:Eu nanocrystals

Strong-luminescence YVO4:Eu nanoparticles were prepared by wet chemical reaction at 155°C. Energy transfer processes from V–O and Eu–O to Eu3+ and f–f transition of Eu3+ are identified. Luminescence intensity is highest when excited through V–O charge transfer band. Also, luminescence intensity increases with heat treatment temperature up to 900°C due to increase of radiative rate. The luminescence emission intensity could be improved after covering the nanoparticles with an undoped shell. Bi-exponential decay is found.

On the mixed order kinetics of the thermoluminescence glow peak

The shape factor of a thermoluminescence (TL) glow peak following mixed order (MO) kinetics has been reinvestigated. A modification of the existing equation of MO kinetics to include the filling factor , where is the initial concentration of trapped electrons and N is the concentration of the electron trap sites) has been proposed. The shifting of peak temperature for a MO kinetics peak with the change of filling factor and hence the irradiation dose absorbed by the sample is reported. A new set of expressions for the evaluation of the activation energy of a TL peak in the light of MO kinetics is presented. The applicability of the MO kinetics model is reported by fitting both the numerically simulated glow peak and the experimentally observed peak of -irradiated NaCl:I and x-irradiated BeO.