A comprehensive study is reported of the photoluminescence properties of ZnS thin films between 1.6 and 320 K grown by metalorganic molecular beam epitaxy and chemical beam epitaxy on GaAs substrates. Both heavy- and light-hole free excitons were observed at low temperatures with linewidths of 7.0 and 5.3 meV, respectively, as well as donor- and acceptor-bound excitons and free-to-bound recombination along with their longitudinal optical (LO) phonon replicas. The free exciton emission was observed up to 320 K, and enabled the room temperature band gap of ZnS to be unambiguously determined as 3.723 eV. The temperature dependence of the peak position, intensity, and linewidth was well described by the conventional empirical relations and by Toyozawa’s exciton line shape theory. The bound exciton peak positions were found to follow the temperature dependence of the band gap whereas the free-to-bound recombination feature was displaced by (1/2)kT above the band gap energy. Thermal quenching of the donor-bound exciton was described by a one-step quenching process with an activation energy of 14.4 meV. The self-activation (SA) center was also observed at 2.846 eV with a linewidth of 410 meV. The temperature dependence of the SA emission was well described by the configuration coordinate model. From the thermal broadening of the SA emission, an average phonon energy of 47.5 meV was determined, in good agreement with the LO phonon energy.

We report a simple, robust, and inexpensive strategy to enable all-inorganic CsPbX3 perovskite nanocrystals (NCs) with a set of markedly improved stabilities, that is, water stability, compositional stability, phase stability, and phase segregation stability via impregnating them in solid organic salt matrices (i.e., metal stearate; MSt). In addition to acting as matrices, MSt also functions as the ligand bound to the surface of CsPbX3 NCs, thereby eliminating the potential damage of NCs commonly encountered during purification as in copious past work. Quite intriguingly, the resulting CsPbX3–MSt nanocomposites display an outstanding suite of stabilities. First, they retain high emission in the presence of water because of the insolubility of MSt in water, signifying their excellent water stability. Second, anion exchange between CsPbBr3–MSt and CsPbI3–MSt nanocomposites is greatly suppressed. This can be ascribed to the efficient coating of MSt, thus effectively isolating the contact between CsPbBr3 and CsPbI3 NCs, reflecting notable compositional stability. Third, remarkably, after being impregnated by MSt, the resulting CsPbI3–MSt nanocomposites sustain the cubic phase of CsPbI3 and high emission, manifesting the strikingly improved phase stability. Finally, phase segregation of CsPbBr1.5I1.5 NCs is arrested via the MSt encapsulation (i.e., no formation of the respective CsPbBr3 and CsPbI3), thus rendering pure and stable photoluminescence (i.e., demonstration of phase segregation stability). Notably, when assembled into typical white light-emitting diode architecture, CsPbBr1.5I1.5–MSt nanocomposites exhibit appealing performance, including a high color rendering index (R a) and a low color temperature (T c). As such, the judicious encapsulation of perovskite NCs into organic salts represents a facile and robust strategy for creating high-quality solid-state luminophores for use in optoelectronic devices.

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The optical and physical properties of a low-voltage phosphor, SrGa2S4:Eu2+, are reviewed. This phosphor has excellent chromaticity and high luminous efficiency at excitation voltages <3 kV and at high drive current (∼100 μA/cm2). At high current densities this phosphor was found to have superior saturation properties compared to current phosphors. This is attributed to the fast decay time of this phosphor, which is expected to enhance its resistance to saturation. Recent studies show that this phosphor has good maintenance properties.