Apparent stretched-exponential luminescence decay in crystalline solids

Abstract

The relaxation of different physical systems has been found to follow the stretched-exponential law, exp½Àðt=tÞ b with 0obo1: In particular, the photoluminescence from porous silicon, nm size silicon in SiO 2 , glassy materials and other solids have been reported in the literature to behave this way. It has been pointed out that the key role for this behavior is played by some kind of disorder in the system. The time constants t reported were between 10 À12 and 10 -2 s. In the present work, it is shown using numerical simulation relevant to the case of trapping controlled luminescence, that the decay from a single crystal with a single trapping state and a single kind of recombination center yields results which agree very well with the stretched-exponential function. Taking trapping parameters in the ranges known in luminescent materials for the stimulation of the decay curves yield different values of the parameter b between 0 and 1, and different values of the time constant t; typically in the micro-to milli-second range. Thus, the stretched-exponential function has been shown to be even more ubiquitous than thought so far, being able to describe the decay of luminescence in an ordered crystal. r

Studies of Basic Electronic Properties of CdTe-Based Solar Cells and Their Evolution During Processing and Stress: Final Technical Report, 16 October 2001 - 31 August 2005

“…This is similar to the stretched exponential parameter that is used to model many natural phenomena [64]. The capacitance transition from to can be spread over a wide range of frequencies and often a good fit is obtained with…”

Determination of the polymerisation rate of a low-toxicity diacetone acrylamide-based holographic photopolymer using Raman spectroscopy

“…Glycerol is a plasticiser and therefore may be promoting increased diffusion of monomer molecules as well as the growing polymer chains, resulting in increased homogeneity of the chain lengths. This may result in less disorder in the system as postulated by Chen [33]. As the recording intensity is increased, this effect becomes less pronounced due to the increased concentration of free radicals.…”

“…He defines b as an exponent that is sensitive to the presence or absence of entanglement of the polymer chains. Chen postulates that b may be related to the distribution of chain lengths, or disorder of the system [33]. As the value for b goes to 1, a normal exponential is obtained which produces a single time constant for the reaction.…”

Photoelectron and Photosensitization Properties of Silicon Nanocrystal Ensembles

“…Indeed, the PL kinetics detected in such systems turns out to be monoexponential with a characteristic time of 0.2-0.8 ms (Vinciguerra, et al, 2000). However, recent theoretical investigation (Chen, 2003) predicts a stretched exponent for PL kinetics even for individual (isolated) nanocrystals in the case where the rate of trapping of photoexcited charge carriers is higher than the rate of their recombination. Note that Chen (Chen, 2003) assumed that nonradiative carrier capture centers should occur in every nc-Si.…”

“…However, recent theoretical investigation (Chen, 2003) predicts a stretched exponent for PL kinetics even for individual (isolated) nanocrystals in the case where the rate of trapping of photoexcited charge carriers is higher than the rate of their recombination. Note that Chen (Chen, 2003) assumed that nonradiative carrier capture centers should occur in every nc-Si. However, this assumption was not supported experimentally for luminescent PS samples, since EPR spectroscopy data demonstrate that the number of defects in 1 cm 3 (about 10 17 ) is much smaller than the number of nc-Si crystals in this volume (about 10 19 -10 20 or 10 21 in the case of a fractal PS structure (Moretti et al, 2007;Nychyporuk et al, 2005)).…”