Increasing the stability of lead halide perovskites (LHPs) is required for integrating them into light-emitting devices. To date, most studies toward this direction have primarily concentrated on improving the chemical stability of green-emitting LHPs. In this work, red-emitting CsPbI 3 −Cs 4 PbI 6 hybrid nanocrystals (NCs) were synthesized with a high photoluminescence (PL) quantum yield of ∼90%. Their hybrid structure was examined via structural (Rietveld) refinement analysis and transmission electron microscopy. Rietveld refinement also revealed that the black polymorph of CsPbI 3 NCs is an orthorhombic perovskite rather than a cubic one. The thermodynamic stability of the CsPbI 3 NCs in Cs 4 PbI 6 matrices is enhanced in both solutions and films for up to several weeks. The enhanced stability of the embedded CsPbI 3 NCs is attributed to the lowering of their Gibbs free energy, as determined on the basis of experimental data. Additionally, the hybrid NCs exhibit unprecedented emission stabilitymaintaining 65% of their original PL efficiency at 150 °C and improved aqueous stability.

To improve and identify next-generation solid-state lighting devices, there is an urgent need to discover new and highly efficient phosphor materials. Currently, the preparation of phosphor materials is considered to be an art rather than science and is based on finding crystal structures that can act as hosts for the activator ions. Thus far, there has been no systematic analysis on how to select host structures for given activator ions such that the synthesized phosphor is efficient. In this review, the general strategies for tuning and enhancing the photoluminescence properties of phosphor materials for white light-emitting diodes are discussed with respect to versatile host materials belonging to the Cs3CoCl5 family. Furthermore, we also discuss several important parameters for constructing the sort diagram for selecting efficient host materials.

Upconversion phosphors have numerous advantages compared to down conversion phosphor materials, such as a weak background interface, low excitation energy, sharp emission lines, and long lifetimes. Conventionally, blue laser diodes are used to obtain strong white light by combining green-and red-emitting phosphors. The blue-excited white-light-emitting devices can be harmful when the blue light penetrates directly into the human body. However, lower energy excited lighting devices does not harm the human body because of their low-energy photons are compatible with the biologically safe window. Hence, we present a prototype device that converts invisible near-infrared light into visible white light. For this, we synthesized orange-emitting Y 2 O 3 :Er 3+ , Yb 3+ and blue-emitting Y 2 O 3 :Tm 3+ , Yb 3+ upconversion phosphors using a solid-state reaction. Using these, phosphor-in-glass (PiG) samples with sintered glass frit were prepared to investigate their optical behavior under lowexcitation energy. The emission color from the stacked PiGs depends on the color balance between the activator ions of Er 3+ , Tm 3+ , and Yb 3+ , and their balance is optimized to obtain a white light. The results might pave the way for designing safe white-light-emitting devices using a low-energy excitation source.

We employed spark plasma sintering (SPS) in the presence of sintering aids to fabricate highquality Ho 3+ ,Yb 3+-co-doped Y 2 O 3 transparent ceramics suitable for use as a laser gain medium, and analyzed their microstructure and optical properties. Ho 3+ ,Yb 3+-co-doped Y 2 O 3 transparent ceramics with different contents of Yb 3+ were fabricated by SPS and exhibited high transparency in both near-infrared and visible regions. All specimens showed high transparency in both the near-infrared and visible-light regions, and sample microstructure was almost unaffected by the amount of doped Yb 3+. The transmission spectra of 1 mol% Yb 3+ doped specimens exhibited transmissivities of 73.4 and 81.0% at wavelengths of 700 and 1500 nm, respectively. Relatively high transmissivity was quickly achieved through the addition of a sintering aid (1 mol% La 2 O 3) which accelerated mass transport during sintering. The effect of Yb 3+ doping on the upconversion photoluminescence of Y 2 O 3 :Ho 3+ ,Yb 3+ was examined. Irradiation at 980 nm resulted in strong green photoluminescence (552 nm) and weak red photoluminescence (669 nm). Excitation at 447 and 980 nm resulted in strong green emission (5 F 4 , 5 S 2 → 5 I 8) from Ho 3+. The effects of Yb 3+ content and laser input power on emission intensity and luminescence decay were investigated in detail. Under excitation at 980 nm, the presence of Yb 3+ increased emission intensity over the entire range, while the opposite behavior was observed under excitation at 447 nm.