Photoluminescence dynamics in ensembles of wide-band-gap nanocrystallites and powders

Abstract

We present photoluminescence (PL) studies of GaN and ZnO nanocrystallites and powders. Our studies show that in addition to the intrinsic photoluminescence characteristics, the photoluminescence properties of the porous media are also a strong function of conditions such as ensemble size and powder density, ultraviolet-laser excitation power, and vacuum state. PL redshifts up to 120 meV were observed for GaN and ZnO crystallites and were attributed to laser heating and heat trapping in the ensemble. The electron-phonon interaction model for GaN indicated ensemble temperature ∼550 K, which is consistent with the finding obtained via high-temperature PL and Raman experiments. The PL in the vacuum state exhibited a significant redshift, ∼80 meV relative to that in air, and the PL of a dense ZnO pellet was found to resemble that of the bulk more than does a loose powder. The PL analyses indicated an excitonic emission at room temperature for both GaN and ZnO crystallites with intensity saturation occurring for large ensembles at high laser power.

Stress and its effect on optical properties of AlN nanorods

“…For excitonic recombination, 1 Ͻ ␣ Ͻ 2; for band-gap emission, ␣ Ϸ 2; ␣ is less than 1 when an impurity is involved in the transition as well as for donoracceptor transition. 18 We found that the PL characteristics of AlN nanorods can be analyzed via Eq. ͑3͒.…”

Multicolor Luminescence from Semiconductor Nanocrystal Composites Tunable in an Electric Field

“…However all results undoubtedly indicate that UV PL has exciton nature. As is well known, a saturation effect of the excitonic emission under high-power excitation is not rarely observed phenomenon (Bergman et al, 2004;Jin et al, 1997). The saturation of the excitonic emission from GaN powder excited in ambient air at RT was ascribed to a thermally activated nonradiative process due to laser heating of particles (Bergman et al, 2004).…”

“…As is well known, a saturation effect of the excitonic emission under high-power excitation is not rarely observed phenomenon (Bergman et al, 2004;Jin et al, 1997). The saturation of the excitonic emission from GaN powder excited in ambient air at RT was ascribed to a thermally activated nonradiative process due to laser heating of particles (Bergman et al, 2004). A slow increase and saturation of the PL intensity of free excitons in a GaInAsSb/GaAlAsSb single-quantumwell structure under higher excitation intensity observed at 10 K was attributed to the exciton screening effect (Jin et al, 1997).…”

“…For excitonic recombination, 1<α<2, for band-gap emission, i.e., electron-hole bimolecular recombination, α~ 2, and α is less than 1 when an impurity is involved in the transitions, as well as for donor-acceptor transitions (Bergman et al, 2004;Jin et al, 1997). Using Eq.…”

Dependence of photoluminescence properties on excitation power in ZnO and ZnCdO microrods

“…A larger µ would lead to a stronger local heating effect. The relation between the PL energy E(P) of UV emission and the www.crt-journal.org © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim excitation power can be written as [24,25] ( ) ( )…”