Luminescence spectra and kinetics of disordered solid solutions

We have studied both theoretically and experimentally the luminescence spectra and kinetics of crystalline, disordered solid solutions after pulsed excitation. First, we present the model calculations of the steady-state luminescence band shape caused by recombination of excitons localized in the wells of random potential induced by disorder. Classification of optically active tail states of the main exciton band into two groups is proposed. The majority of the states responsible for the optical absorption corresponds to the group of extended states belonging to the percolation cluster, whereas only a relatively small group of “radiative” states forms the steady-state luminescence band. The continuum percolation theory is applied to distinguish the “radiative” localized states, which are isolated in space and have no ways for nonradiative transitions along the tail states. It is found that the analysis of the exciton-phonon interaction gives the information about the character of the localization of excitons. We have shown that the model used describes quite well the experimental cw spectra of CdS(1−c)Sec and ZnSe(1−c)Tec solid solutions. Further, the experimental results are presented for the temporal evolution of the luminescence band. It is shown that the changes of band shape with time come from the interplay of population dynamics of extended states and spatially isolated “radiative” states. Finally, the measurements of the decay of the spectrally integrated luminescence intensity at long delay times are presented. It is shown that the observed temporal behavior can be described in terms of relaxation of separated pairs followed by subsequent exciton formation and radiative recombination. Electron tunneling processes are supposed to be responsible for the luminescence in the long-time limit at excitation below the exciton mobility edge. At excitation by photons with higher energies the diffusion of electrons can account for the observed behavior of the luminescence

Segregation of In to dislocations in InGaN.

Dislocations are one-dimensional topological defects that occur frequently in functional thin film materials and that are known to degrade the performance of InxGa1-xN-based optoelectronic devices. Here, we show that large local deviations in alloy composition and atomic structure are expected to occur in and around dislocation cores in InxGa(1-x)N alloy thin films. We present energy-dispersive X-ray spectroscopy data supporting this result. The methods presented here are also widely applicable for predicting composition fluctuations associated with strain fields in other inorganic functional material thin films.This work was funded in part by the Cambridge Commonwealth trust, St. John’s College and the EPSRC. SKR is funded through the Cambridge-India Partnership Fund and Indian Institute of Technology Bombay via a scholarship. MAM acknowledges support from the Royal Society through a University Research Fellowship. Additional support was provided by the EPSRC through the UK National Facility for Aberration-Corrected STEM (SuperSTEM). The Titan 80- 200kV ChemiSTEMTM was funded through HM Government (UK) and is associated with the capabilities of the University of Manchester Nuclear Manufacturing (NUMAN) capabilities. SJH acknowledges funding from the Defence Treat Reduction Agency (DTRA) USA (grant number HDTRA1-12-1-0013).This is the accepted manuscript. The final version is available at http://pubs.acs.org/doi/abs/10.1021/nl5036513

High-pressure behavior of thiospinel CuCr2S4

none4noneMATTEO ALVARO; FABRIZIO NESTOLA; NANCY ROSS; M.CHIARA DOMENEGHETTI AND LEONID REZNITSKYAlvaro, Matteo; Nestola, Fabrizio; Nancy, Ross; M., CHIARA DOMENEGHETTI AND LEONID REZNITSK