B.P. Chandra

Theoretical approach to the lyoluminescence of alkali halides

Abstract When previously irradiated halide crystals are dissolved into a solvent like water, the radiative recombination of hydrated electrons with the holes on the surface of the crystallites, gives rise to the light emission. The intensity of lyoluminescence (LL) emission depends on different parameters and it can be expressed as I = ηβγαn F N 0 (β − α) { exp (−αt) − exp (−βt)} , where η is the probability of radiative recombination, β the rate constant for the recombination of hydrated electrons with holes, γ the factor correlating the number of hydrated electrons and the number of dissolved F-centres, α the rate of dissolution of solute in the solvent, nF the density of F-centres, N0 the initial number of the molecules of solute, and t the time of dissolution. The equation shows that the LL intensity should initially increase with time, attain an optimum value and then it should decrease exponentially with time. As α increases with temperature, an increase in the value of I with temperature is expected. However, at higher temperature thermal bleaching takes place, and consequently the LL intensity should be maximum at a particular temperature. The LL intensity initially increases and then tends to attain a saturation value for higher mass of the solute added into the solvent. A good qualitative correlation is found between the experimental and theoretical results.

Chemical route synthesis dependent particle size of Mn activated ZnS nanophosphors

The synthesis and optical properties of Mn activated ZnS nanoparticles are reported in this paper. Nanoparticles of zinc sulphide were prepared by chemical route technique; whereas mercaptoethanol (ME) was used as the capping agent. The particle size of such nanocrystals was measured using XRD, SEM and TEM patterns and was found to be in between 3 nm to 5 nm. The blue-shift in the absorption spectra was found with reducing size of the nanoparticles. It was also found that the change in Mn concentrations does not influence the particle size and blue-shift in the absorption spectra. The optical absorption edge was found at 296 nm for all the doped samples for fixed concentration of capping agent. The particle size of nanoparticle was calculated both theoretically and experimentally, which is nearly the same. The FTIR spectra inferred that the stabilising agent passivates the surface of the particles.

Effect of Molar Concentration on Optical Absorption Spectra of ZnS:Mn Nanoparticles

The present paper reports the synthesis and characterization of luminescent nanocrystals of manganese doped zinc sulphide. Nanocrystals of zinc sulphide were prepared by chemical precipitation method using the solution of zinc chloride, sodium sulphide, manganese chloride and mercaptoethanol was used as the capping agent. It was found that change in the molar concentration changes the particle size. The particle size of such nanocrystals was measured using XRD pattern and it is found to be in between 3 nm – 5 nm. The blue-shift in absorption spectra was found with reducing size of the nanoparticles