Influence of Oxidation on Temperature-Dependent Photoluminescence Properties of Hydrogen-Terminated Silicon Nanocrystals

Abstract

In this study, we investigate temperature-dependent photoluminescence (PL) in three samples of hydrogen-terminated silicon nanocrystals (ncSi-H) with different levels of surface oxidation.ncSi-H was oxidized by exposure to ambient air for 0 h, 24 h, or 48 h. The PL spectra as a function of temperature ranging between room temperature (~297 K) and 4 K are measured to elucidate the underlying physics of the PL spectra influenced by the surface oxidation of ncSi-H. There are striking differences in the evolution of PL spectra according to the surface oxidation level. The PL intensity increases as the temperature decreases. ForncSi-H with a smaller amount of oxide, the PL intensity is nearly saturated at 90 K. In contrast, the PL intensity decreases even below 90 K for the heavilyoxidized ncSi-H. For all the samples, full-width at half maxima (FWHM)decreases as the temperature decreases. The plots of the PL peak energy as a function of temperature can be reproduced with an equation where the average phonon energy and other parameters are calculated.

Size-Dependent Photothermal Performance of Silicon Quantum Dots

“…Unlike a previous study reporting the temperature dependence of PL spectra for oxide-encapsulated SiQDs, 52 the PL intensity does not increase from 4.2 to 30 K. It has been recently established that this rise in the lowest temperature range might be due to amorphous silica on the surface of H-SiQD. 53 Thus, the oxidation degree of our samples is too small to influence the PL properties, which is consistent with the ATR-FTIR study.…”

“…Figure plots the PL intensity at each monitoring temperature normalized with respect to the PL intensity value at 300 K. Clearly, all samples demonstrate a continuously decreasing trend as the temperature increases. Unlike a previous study reporting the temperature dependence of PL spectra for oxide-encapsulated SiQDs, the PL intensity does not increase from 4.2 to 30 K. It has been recently established that this rise in the lowest temperature range might be due to amorphous silica on the surface of H-SiQD . Thus, the oxidation degree of our samples is too small to influence the PL properties, which is consistent with the ATR-FTIR study.…”

A novel sustainable and green mechanochemical route from a (HSiO1.5)n polymer to emissive silicon nanocrystals

“…of free-standing Si NCs are significantly influenced by the core-state particle size, and the functionalized surface involving the chemical structure of passivated groups, the remaining amount of Si-H and dangling bonds, as well as their coverage ratio. 1,2,[75][76][77][78] Although it is difficult to compare each component since an exact identical condition is lacking, it can be suggested that our prepared Si NCs exhibiting an absolute QY of 9.8% is quite comparable to those conventional ones (as given in Table S1, ESI †). It has been reported that these free-standing Si NCs possess functional surface groups that enable a good dispersibility in polar solvents and long-term chemical stability.…”

Distinct Acoustic and Optical Phonon Dependences on Particle Size, Oxidation, and Temperature in Silicon Nanocrystals

“…Evidence shows that phonons can play an important role in the PL of silicon nanocrystals. The PL lifetime in spatially confined silicon is approximately 3 orders of magnitude longer than that of direct bandgap transitions. − PL observed under resonant excitation is related to transverse optical and transverse acoustic (TA) phonon modes of bulk crystalline silicon to account for momentum conservation. − Additionally, the temperature dependence of the PL emission wavelength of silicon nanocrystals also supports the mechanism of phonon-assisted indirect transition. , Furthermore, calculations with a valence force-field model find that phonon-assisted transitions dominate over the full range of particle sizes . However, a systematic experimental study on phonon dynamics in the whole reciprocal space of spatially confined silicon systems remains limited. − …”

“…44−46 Additionally, the temperature dependence of the PL emission wavelength of silicon nanocrystals also supports the mechanism of phonon-assisted indirect transition. 43,47 Furthermore, calculations with a valence force-field model find that phononassisted transitions dominate over the full range of particle sizes. 48 However, a systematic experimental study on phonon dynamics in the whole reciprocal space of spatially confined silicon systems remains limited.…”