Exciton self-trapping in AgCl nanocrystals

Abstract

Self-trapping of excitons is reported in AgCl nanocrystals embedded in a crystalline KCl matrix. The particles, observed by atomic force microscopy, have radii of several nanometers. Due to the spatial confinement only recombination of the self-trapped exciton ͑STE͒ is observed. STE(Br Ϫ ) and donor-acceptor pair recombination are absent. The time and temperature behavior of the emission is found to be significantly different from that in bulk AgCl. It is concluded that this is due to different self-trapped exciton configurations: The diffuse electron is spatially confined and centered in the nanocrystal whereas the compact hole, selftrapped at different lattice sites, causes variations in wave-function overlap in the different STEs. Optically detected magnetic resonance measurements reveal changes in g-values and a decrease by a factor of two in the magnitude of the zero-field splitting of the triplet state. They also demonstrate that the AgCl nanocrystal lattice axes are oriented along the axes of the KCl matrix.

Effects of organic moieties on the photoluminescence spectra of perovskite-type tin bromide based compounds

“…In a few words, the shape and intensity of PL and OA spectra of CH 3 NH 3 SnBr 3 , varies from sample to sample (see also [1,2]) and the perfect reproducibility is difficult at ambient conditions. However, with 350 nm excitation the PL spectrum is dominated by a broad and strong band at ca 599 nm, attributed to the radiative decay of self-trapped excitons of SnBr 3 moiety, as it is observed from other semiconductors [11,[33][34][35][36]. The differences in the position and the intensity between the PL spectra b´ and c´, perhaps is a consequence of the amount of energy transfer of several states to the trapped exciton state.…”

“…It has been reported that the PL spectrum of SnBr 2 at low temperature values (ca 12K) exhibits a band at ca 571 nm, which has been attributed to radiative decay of self-trapped excitons [27,[33][34][35], and some weaker bands. The intensity of the 571nm band decreases, when the sample is warmed above 50 K, and PL almost disappears at 100 K. Also, CH 3 NH 3 Br is a white in color solid, which does not show any PL band at room temperature.…”

“…The position of the spectral bands occur in the order λ(3D)>λ(2D)>λ(1D), where λ is the wavelength. They can be prepared from their solutions or from melts in single crystal form or in particulate forms (grinding powders, suspensions in several solvents, and dispersions in several matrices) [6,7,[30][31][32][33][34][35][36][37]. In the particulate forms, the products of the reactions are in equilibrium with their precursors [8][9][10], e.g.…”

Optical limiting of niobic tellurite glass induced by self-trapped exciton absorption of the AgCl nanocrystal dopant

“…Because of the Cl − color center in the glass matrix, the doped samples became darker with the heat treatment going on. The AgCl defects may lead to the lattice deformation of the AgCl nanocrystal, which will give rise to the self-trapped exciton band [16,18] . As shown in Figure 1, the absorption tails will gradually shift to red-side with the heat treatment going on.…”

“…The absorption band of free excitons will redshift (the Stokes shift) [16] , and the self-trapped exciton will be generated. Till now, the self-trapped exciton of the AgCl nanocrystals has only been observed in the AgCl doped alkali halide host matrix [17,18] , and there has been no report on the glass host matrix. In this work, the AgCl nanocrystal doped niobic tellurite glass was prepared with the melting-quenching and heat treatment method, the self-trapped exciton absorption band of the AgCl nanocrystal was discussed and analyzed, and fi-…”