Continuous-wave lasing from perovskites embedded microcavities

• Main Author: Zhang, Hongbo
• Other Authors: Yu Ting
• Format: Thesis-Doctor of Philosophy
• Language: English
• Published: Nanyang Technological University 2021
• Subjects: Science::Physics::Optics and light
• Online Access: https://hdl.handle.net/10356/151746
• Institution: Nanyang Technological University

The emerging lead halide perovskite materials with a basic form of ABX3 have aroused enormous interest due to their underlying rich physics and promising applications in optics, electronics, and optoelectronics. In particular, trigged by the unprecedented success in photovoltaics, lead halide perovskites have attracted more and more attention because of their superior properties such as a direct-band gap, strong excitonic effects, high quantum efficiency, and broadly tunable emission wavelengths. Besides, the facile solution processability and defect tolerance of metal halide perovskites guarantee low-cost light-emitting devices. In the past few years, significant efforts have been made to achieve lasing emission of metal halide perovskites under pulsed pumping. However, the study of continuous-wave (CW) perovskite laser, which is regarded as a significant milestone towards the electrically pumped laser, is still at the early stage. Thus, further optimization of light-emitting materials and optical confinement is highly demanded to advance the development of CW pumped perovskite lasers. In this thesis, I mainly focus on the preparation of high-quality lead halide perovskites and the systematic investigation of CW lasing from both organic and inorganic perovskites embedded in microcavities. The high-quality single-crystalline methylammonium lead bromide (MAPbBr3) nanoplates were grown by a facile two-step solution method, with the aim of the development of the efficient CW pumped laser. The phase transition from the cubic to tetragonal to orthorhombic phase have been recorded by in-situ temperature-dependent Raman spectroscopy, and the pronounced PL enhancement was observed at 80 K. Furthermore, the representative free exciton emission with an inhomogeneous broadening of 3.94 meV and the binding energy of 21.1meV have been demonstrated by in-situ temperature-dependent PL spectroscopy from 13.5 to 73.5 K, indicating the brilliant optical quality of the single-crystalline MAPbBr3 nanoplates. By embedding the as-fabricated MAPbBr3 into the vertical microcavity, CW lasing with a low threshold of 55.2 W cm-2 and a high Q-factor of 1140 have been demonstrated at 80 K, which is attributed to strong optical confinement in the high-Q cavity and significant PL enhancement at low temperature. These findings envisage the future applications of single-crystalline metal halide perovskites in practicable laser devices. All-inorganic cesium lead bromide (CsPbBr3) quantum dots (QDs) are considered as promising candidates to achieve room temperature CW pumped lasing due to their large exciton binding energy, near-unity photoluminescence quantum yield, and high environmental stability. Here, the high-quality CsPbBr3 QDs, prepared by a hot-injection method, were employed as the gain medium and sandwiched by two sets of high-reflectivity DBRs to form a high Q-factor vertical-cavity surface-emitting laser (VCSEL). The as-prepared CsPbBr3 QDs were diluted and mixed with PMMA to ensure their sparse dispersion in the microcavity, showing single-mode CW lasing with a relatively low threshold of 8.8 W cm-2 and high Q-factor of 1787 at room temperature. The CsPbBr3 QDs VCSEL held outstanding environmental stability, which can sustain more than 5 min and conserve the lasing characteristic after one-year of storage in the ambient condition. This work sheds light on the realization of practical coherent light sources based on lead halide perovskites. 2D layered lead halide perovskites with the large exciton binding energy, efficient radiative recombination and outstanding environmental stability are regards as supreme candidates for realizing ultralow threshold lasers. Here, the phenylethylammonium lead iodide [(PEA)2PbI4] thin flakes, exfoliated from the solution-processed millimeter-sized single crystal, were utilized as gain media to construct a VCSEL, which presents the robust single-mode CW lasing operation with an ultra-low threshold of 5.7 W cm−2 at room temperature, attributed to strong optical confinement in the high-Q cavity. Moreover, the multi-mode emission has been synchronously discussed, which can be explained by the change of the cavity length resulting from the unintentional roughness of the exfoliated flake. This work opens up a new window for developing novel 2D VCSELs based on the layered lead halide perovskites. In summary, this thesis depicts the systematic exploration of CW lasers developed by both organic and inorganic perovskites sandwiched in microcavities with low or room-temperature operations. These findings provide a strategy to design and fabricate solution-based perovskite VCSELs and mark a significant step towards the next-generation of coherent light sources.