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Perovskite-type lead halides exhibit promising performances in optoelectronic applications, for which lasers are one of the most promising applications. Although the bulk structure has some advantages, perovskite has additional advantages at the nanoscale owing to its high crystallinity given by a lower trap density. Although the nanoscale can produce efficient light emission, its comparatively poor chemical and colloidal stability limits further development of devices based on this material. Nevertheless, bulk perovskites are promising as optical amplifiers. There has been some developmental progress in the study of optical response and amplified spontaneous emission (ASE) as a benchmark for perovskite bulk phase laser applications. Therefore, to achieve high photoluminescence quantum yields (PLQYs) and large optical gains, material development is essential. One of the aspects in which these goals can be achieved is the incorporation of a bulk structure of high-quality crystallization films based on inorganic perovskite, such as cesium lead halide (CsPb(Br/Cl)3), in polymethyl methacrylate (PMMA) polymer and encapsulation with the optimal thickness of the polymer to achieve complete surface coverage, prevent degradation, surface states, and surface defects, and suppress emission at depth. Sequential evaporation of the perovskite precursors using a single-source thermal evaporation technique (TET) effectively deposited two layers. The PL and ASEs of the bare and modified films with a thickness of 400 nm PMMA were demonstrated. The encapsulation layer maintained the quantum yield of the perovskite layer in the air for more than two years while providing added optical gain compared to the bare film. Under a picosecond pulse laser, the PL wavelength of single excitons and ASE wavelength associated with the stimulated decay of bi-excitons were achieved. The two ASE bands were highly correlated and competed with each other; they were classified as exciton and bi-exciton recombination, respectively. According to the ASE results, bi-exciton emission could be observed in an ultrastable CsPb(Br/Cl)3 film modified by PMMA with a very low excitation energy density of 110 µJ/cm2. Compared with the bare film, the ASE threshold was lowered by approximately 5%. A bi-exciton has a binding energy (26.78 meV) smaller than the binding energy of the exciton (70.20 meV). [ABSTRACT FROM AUTHOR]

The high crystal quality of formamidium lead bromide perovskite (CH(NH2)2PbBr3 = FAPbBr3) was infiltrated in a mesoporous TiO2 network. Then, high-quality FAPbBr3 films were evaluated as active lasing media, and were irradiated with a picosecond pulsed laser to demonstrate amplified spontaneous emission (ASE), which is a better benchmark of its intrinsic suitability for gain applications. The behavior was investigated using two excitation wavelengths of 440 nm and 500 nm. Due to the wavelength-dependent absorbance spectrum and the presence of a surface adsorption layer that could be reduced using the shorter 440 nm wavelength, the ASE power dependence was strongly reliant on the excitation wavelength. The ASE state was achieved with a threshold energy density of ~200 µJ/cm2 under 440 nm excitation. Excitation at 500 nm, on the other hand, needed a higher threshold energy density of ~255 µJ/cm2. The ASE threshold carrier density, on the other hand, was expected to be ~4.5 × 1018 cm−3 for both excitations. A redshift of the ASE peak was detected as bandgap renormalization (BGR), and a BGR constant of ~5–7 × 10−9 eV cm was obtained. [ABSTRACT FROM AUTHOR]

High-quality inorganic cesium lead halide perovskite CsPb(Br0.5Cl0.5)3 thin films were successfully achieved through evaporation of the precursors and deposition sequentially by a single-source thermal evaporation system. The different melting points of the precursors were enabled us to evaporate precursors one by one in one trip. The resulting films through its fabrication were smooth and pinhole-free. Furthermore, this technique enabled complete surface coverage by high-quality perovskite crystallization and more moisture stability oppositely of that produce by solution-processed. Then the perovskite films were encapsulated by evaporated a polymethyl methacrylate (PMMA) polymer as a specialized surface passivation approach with various thicknesses. The blue emission, high photoluminescence quantum yield (PLQY), stable, and low threshold of amplified spontaneous emission (ASE) properties of CsPb(Br0.5Cl0.5)3 films in the bulk structure at room temperature were achieved. The effects of the surface-passivation layer and its thickness on the optical response were examined. Detailed analysis of the dependence of ASE properties on the surface passivation layer thickness was performed, and it was determined this achieves performance optimization. The ASE characteristics of bare perovskite thin film were influenced by the incorporation of the PMMA with various thicknesses. The improvement to the surface layer of perovskite thin films compared to that of the bare perovskite thin film was attributed to the combination of thermal evaporation deposition and surface encapsulation. The best results were achieved when using a low PMMA thickness up to 100 nm and reducing the ASE threshold by ~11 μJ/cm2 when compared with free-encapsulation and by ~13 μJ/cm2 when encapsulation occurs at 200 nm or thicker. Compared to the bare CsPb(Br0.5Cl0.5)3, ASE reduced 1.1 times when the PMMA thickness was 100 nm. [ABSTRACT FROM AUTHOR]

Organic–inorganic halide organometal perovskites have demonstrated very promising performance in optoelectronic applications, but their relatively poor chemical and colloidal stability hampers the further improvement of devices based on these materials. Perovskite material engineering is crucial for achieving high photoluminescence quantum yields (PLQYs) and long stability. Herein, these goals are attained by incorporating bulk-structure CsPbBr3, which prevents colloidal degradation, into polymethyl methacrylate (PMMA) polymer in thin-disk form. This technology can potentially realize future disk lasers with no optical and structural contributions from the polymer. The polycrystalline CsPbBr3 perovskite particles were simply obtained by using a mechanical processing technique. The CsPbBr3 was then incorporated into the PMMA polymer using a solution blending method. The polymer enhanced the PLQYs by removing the surface trap states and increasing the water resistance and stability under ambient conditions. In our experimental investigation, the CsPbBr3/PMMA composites were extraordinarily stable and remained strongly luminescent after water immersion for three months and air exposure for over one year, maintaining 80% of their initial photoluminescence intensity. The CsPbBr3/PMMA thin disk produced amplified spontaneous emission for a long time in air and for more than two weeks in water. [ABSTRACT FROM AUTHOR]

Amplified spontaneous emission (ASE) threshold in CsPbBr 3 quantum dot films is systematically reduced by introducing high quality TiO 2 compact layer grown by atomic-layer deposition. Uniform and pinhole-free TiO 2 films of thickness 10, 20 and 50 nm are used as a substrates for CsPbBr 3 quantum dot films to enhance amplified spontaneous emission performance. The reduction is attributed indirectly to the improved morphology of TiO 2 compact layer and subsequently CsPbBr 3 active layer as grown on better quality substrates. This is quantified by the reduced roughness of the obtained films to less than 5 nm with 50 nm TiO 2 substrate. Considering the used growth method for the quantum dot film, the improved substrate morphology maintains better the structure of the used quantum dots in the precursor solution. This results in better absorption and hence lower threshold of ASE. Besides that, the improved film quality results further in reducing light scattering and hence additional slight optical enhancement. The work demonstrates a potential venue to reduce the amplified spontaneous emission threshold of quantum dot films and therefore enhanced their optical performance. [ABSTRACT FROM AUTHOR]