Spectral Dependencies of the Stretched Exponential Dispersion Factor and Photoluminescence Quantum Yield as a Common Feature of Nanocrystalline Si

Abstract

Herein, the spectral dependencies of the dispersion factor β (from the stretched exponential function) and photoluminescence (PL) quantum yield (QY) of silicon nanocrystals (Si NCs) are thoroughly studied. Spectrally resolved PL decay kinetics of Si NCs in both liquid and solid samples are measured and their corresponding distributions of rates are retrieved by means of the hybrid maximum‐entropy method. This enables us to demonstrate a direct correlation of dispersion factor β with the width of rate distribution. Here, the evidence of the same step‐like spectral dependence of rate distribution widths (dispersion factor) for different forms of nanocrystalline silicon (including porous silicon and chemically synthesized Si NCs) is presented suggesting intrinsic (core‐related) origin of rate distributions. Spectral dependence of normalized QY of Si NCs reveals two characteristic peaks with spectral positions at ≈1.42 and ≈1.68 eV. A similar peak in QY spectral dependence of CdSe quantum dots (QDs) is found, which suggests its common origin regardless the material of semiconductor QDs.

Photoluminescent Si/SiO2 Core/Shell Quantum Dots Prepared by High-Pressure Water Vapor Annealing for Solar Concentrators, Light-Emitting Devices, and Bioimaging

“…Figure a shows the measured PL intensities of Si QDs oxidized from 7.5 to 17 bar. Increasing the pressure of the vessel generally blue-shifts the PL of the Si/SiO 2 QDs, and the intensities decrease as the peak PL wavelength strays from 850 nm, where generally the optimal PLQY of Si QDs is observed . Similarly, Figure b shows that both the PLQY and the peak PL wavelength decrease with increasing pressure.…”

“…This may point to the ensemble of QDs stabilizing over time as dispersion factors closer to 1.0 (single-exponential decay) indicate a closer proximity of the system to the ideal, isolated QD system. 59 These results show that the PL of Si/SiO 2 QDs can be tuned simply by tuning the pressure during HWA treatment, which can be considered a design parameter to tailor Si QD luminescence properties to specific applications.…”

Trap-State-Induced Becquerel Type of Photoluminescence Decay in DPA-Activated Silicon Nanocrystals

“…The accuracy of the characterization of the shape of the PL decay can be assessed using the planarity condition for the ACF from eq . Moreover, this difference in the shape of the PL decay can be manifested also by employing the maximum entropy method, , which can be applied to deduce the distribution of lifetimes from PL decay curves without a priori assuming any particular shape of the fitting function. For more information, see section S3 in Supporting Information for the maximum-entropy-method analysis, and a series of papers , for a detailed treatment of the relationship between the underlying distribution of lifetimes/decay rates and the corresponding decay law.…”

Advances in Silicon‐Nanoelectronics, Nanostructures and High‐Efficiency Si‐Photovoltaics

“…One of them is the Feature Article by Greben, Khoroshyy, and Valenta about spectral dependencies of the stretched exponential decay of the photoluminescence and the quantum yield in nanocrystalline Si. [1] Two more papers also deal with Si nanocrystals, one with the enhancement of the photoluminescence by a metal membrane, [2] the other one with the general crystallization behavior. [3] Four contributions focus on photovoltaic applications: An improved wet-chemical processing of Si for heterojunction solar cells, [4] a deeper understanding of contact resistivity measurements via the TLM-method, [5] and the fabrication of nanostructures for enhanced light absorption by cryogenic dry etching [6] and by using self-assembled nanosphere-lithography masks.…”

“…There are in total 11 articles in this Special Issue. One of them is the Feature Article by Greben, Khoroshyy, and Valenta about spectral dependencies of the stretched exponential decay of the photoluminescence and the quantum yield in nanocrystalline Si . Two more papers also deal with Si nanocrystals, one with the enhancement of the photoluminescence by a metal membrane, the other one with the general crystallization behavior .…”