Study on Growth Kinetics of CdSe Nanocrystals with a New Model

A model which involves both bulk diffusion process and surface reaction process has been developed for describing the growth behaviour of nanoparticles. When the model is employed, hypothesising that either of the processes alone dominates the overall growth process is unnecessary. Conversely, the relative magnitude of contributions from both processes could be obtained from the model. Using this model in our system, the growth process of CdSe QDs demonstrated two different growth stages. During the first stage, the growth of CdSe QDs was dominated by bulk diffusion, whereas, neither the bulk diffusion process nor the surface reaction process could be neglected during the later stage. At last, we successfully modelled the Ostwald ripening of CdSe QDs with LSW theories

ESR and TL mechanism in CaSO4 : Ag co-doped phosphors

Thermoluminescence (TL) studies have been carried out on CaSO4 : Mn, CaSO4 : Ag, Mn, CaSO4 : Ag, Nd, CaSO4 : Ag, Mn, Nd, CaSO4 : Ag, Zr and CaSO4 : Ag, Mn, Zr phosphors. It is found that TL at 360 degrees C in CaSO4 : Ag, Mn, Nd is about 40 times that of CaSO4 : Ag, Mn and about 170 times that of CaSO4 : Ag, Nd. This shows that the presence of an efficient luminescent centre (Mn2+) as well as a trivalent impurity (such as Nd3+ or Y3+) is important for enhancement of TL at 360 degrees C in the CaSO4 : Ag, Mn, Nd phosphor system. Electron spin resonance (ESR) studies show that the peak at 360 degrees C correlates with an Ag2+ centre formed due to gamma-irradiation and observable only below -170 degrees C. The Ag2+ centre is characterized by an axial g-tensor with principal values g(parallel to) = 2.38 and g(perpendicular to) = 2.41. ESR studies further indicate that the precursor to a centre observable at low temperature (-170 degrees C) appears to act as the recombination centre for the TL peak at 360 degrees C. The low temperature centre is characterized by the g-values g(vertical bar vertical bar) = 2.0023 and g(perpendicular to) = 2.0038 and is assigned to the SO3- radical