Perovskite nanocrystals (PeNCs) are attractive in high-color gamut display technology as light converters which can achieve saturated green and red lights, respectively. However, PeNCs are intrinsically fragile against ambient conditions, such as moisture and oxygen and it is hard to maintain their performance in long-term operation. In this work, a new hierarchical encapsulation method is proposed, integrated with surface modification by halide ions protection, nano-scaled encapsulation by in situ capping SiO ₂ and embedding into poly (methyl methacrylate) (PMMA) matrix composites, to achieve a stable perovskite light converting composite sheet for LED remote-type encapsulation. The storage stability, as well as the operational stability of perovskite composites, were confirmed by the spectra evolution from encapsulated LEDs with normalized blue emission intensity. The 2D maps of spectra and aging measurement indicate that the silica encapsulation can well protect the PeNCs in the PMMA matrix from the ambient circumstance during a long-term storage process. Additionally, the hierarchical encapsulation for PeNCs/silica/PMMA showed better operational stability than the direct encapsulation of PeNCs/PMMA, and the correspondent Commission Internationale de L’Eclairage color coordinates tracking also indicated more stable color properties, which demonstrates the great potential in photoluminescent display applications.

Optical gain enhancement of two-dimensional CsPbBr₃ nanosheets was studied when the amplified spontaneous emission is guided by a patterned structure of polyurethane-acrylate. Given the uncertainties and pitfalls in retrieving a gain coefficient from the variable stripe length method, a gain contour $$g(\hslash \omega ,x)$$g ( ℏ ω , x ) was obtained in the plane of spectrum energy (ℏω) and stripe length (x), whereby an average gain was obtained, and gain saturation was analysed. Excitation and temperature dependence of the gain contour show that the waveguide enhances both gain and thermal stability due to the increased optical confinement and heat dissipation, and the gain origins were attributed to the two-dimensional excitons and the localized states.

The temperature-dependent photoluminescence of CsPbBr₃/SiO₂ and CsPbI₃/SiO₂ nanocrystals was investigated to understand the thermal stability of SiO₂ encapsulation. At increased temperature, intensity quenching, linewidth broadening, energy level shift, and decay dynamics were evaluated as quantified parameters. Comprehensive analysis of these parameters supports that CsPbI₃/SiO₂ nanocrystals show a stronger interaction with phonons compared with CsPbBr₃/SiO₂ nanocrystals. Despite SiO₂ encapsulation, we conclude that trapping states are still present and the degree of localization can be characterized in terms of short-lived decay time and thermal activation energy.

The optical modal gain of Cd_0.6Zn_0.4Te/ZnTe double quantum dots was measured using a variable stripe length method, where large and small quantum dots are separated with a ZnTe layer. With a large (~18 nm) separation layer thickness of ZnTe, two gain spectra were observed, which correspond to the confined exciton levels of the large and small quantum dots, respectively. With a small (~6 nm) separation layer thickness of ZnTe, a merged single gain spectrum was observed. This can be attributed to a coupled state between large and small quantum dots. Because the density of large quantum dots (4 × 10¹⁰ cm⁻²) is twice the density of small quantum dots (2 × 10¹⁰ cm⁻²), the density of the coupled quantum dots is determined by that of small quantum dots. As a result, we found that the peak gain (123.9 ± 9.2 cm⁻¹) with the 6 nm separation layer is comparable to that (125.2 ± 29.2 cm⁻¹) of the small quantum dots with the 18 nm separation layer.