Temperature dependence of radiative lifetimes, optical and electronic properties of silicon nanocrystals capped with various organic ligands

One-dimensional scintillator film with benign grain boundaries for high-resolution and fast x-ray imaging

Fast and high-resolution x-ray imaging demands scintillator films with negligible afterglow, high scintillation yield, and minimized cross-talk. However, grain boundaries (GBs) are abundant in polycrystalline scintillator film, and, for current inorganic scintillators, detrimental dangling bonds at GBs inevitably extend radioluminescence lifetime and increase nonradiative recombination loss, deteriorating afterglow and scintillation yield. Here, we demonstrate that scintillators with one-dimensional (1D) crystal structure, Cs₅Cu₃Cl₆I₂ explored here, possess benign GBs without dangling bonds, yielding nearly identical afterglow and scintillation yield for single crystals and polycrystalline films. Because of its 1D crystal structure, Cs₅Cu₃Cl₆I₂ films with desired columnar morphology are easily obtained via close space sublimation, exhibit negligible afterglow (0.1% at 10 ms) and high scintillation yield (1.2 times of CsI:Tl). We have also demonstrated fast x-ray imaging with 27 line pairs mm^-1 resolution and frame rate up to 33 fps, surpassing most existing scintillators. We believe that the 1D scintillators can greatly boost x-ray imaging performance.

Multi-carrier processes in halogenated Si nanocrystals

We study theoretically an effect of passivation with Cl and Br on Auger recombination and multiple exciton generation in silicon nanocrystal Si₃₁₇X₁₇₂, with X being the passivating element. The nanocrystal electronic structure and rates of these processes are calculated using time-dependent density functional theory. Comparison with the H-passivated Si nanocrystal shows that the bromine coating, despite having less electronegativity, affects the electronic structure and transition rates more than the chlorine one due to the stronger structural perturbations caused by the greater surface atoms. Certain electron-hole asymmetry in both of the considered multi-carrier processes is revealed for the Br-coated silicon nanocrystal: the processes become faster if initiated by holes and slower (or invariable on the whole) if initiated by electrons. On the contrary, the chlorine coating weakly influences the multi-carrier processes.

Introductory lecture: origins and applications of efficient visible photoluminescence from silicon-based nanostructures

This review highlights many spectroscopy-based studies and selected phenomenological studies of silicon-based nanostructures that provide insight into their likely PL mechanisms, and also covers six application areas.