Whispering Gallery Mode Lasing from Perovskite Polygonal Microcavities via Femtosecond Laser Direct Writing

Tuning the Triplet State of Ligands on FAPbBr3 Quantum Dots toward Low-Threshold Distributed Feedback Lasers

Herein, the influence of ligand triplet energy on carrier transfer dynamics and optical gain behaviors of quantum dots (QDs) was investigated using FAPbBr3 QDs capped by phenylethylamine (PEA) and 2-(2-naphthyl)ethylamine (NEA) molecules. Through analysis of steady-state and transient spectroscopic data as well as the energy level structure of QD-ligand complexes, a very close triplet energy gap between QDs and NEA was demonstrated, which could act as an effective energy transfer channel between QDs and ligands. The setup of this energy-transfer channel greatly reduced the carrier density in QDs under high pump fluences, contributing to a lasing threshold as low as 6.1 μJ/cm2. The proposed ligand triplet regulation strategy provided new insights into carrier recombination dynamic control and may also be useful for other optoelectronic devices such as solar cells, light-emitting diodes, and photodetectors.

Bandgap-Tunable Halide Perovskite Quantum Dots Enabled by Femtosecond Laser Patterning for Full-Color and High-Resolution Display

Perovskite quantum dots (PQDs) have garnered significant attention for their exceptional optoelectronic properties, yet achieving precise luminescence control often involves complex chemical processes, and traditional display technologies face material and environmental limitations. In this study, we present an innovative approach utilizing three distinct halide perovskite quantum dot solutions to achieve tunable emission properties without additional chemical modifications. By employing femtosecond laser patterning, we successfully fabricated high-resolution (1.5 μm spacing), full-color (410-710 nm) quantum dot patterns with excellent environmental stability. This method eliminates the need for excessive chemical reagents and intricate masking steps, significantly streamlining the fabrication process and enhancing efficiency. Our findings highlight the potential of combining bandgap engineering with advanced patterning techniques, offering a practical foundation for green synthesis and simplified manufacturing processes in next-generation display technologies.

Single-crystal CsPbBr3-based vertical cavity surface emitting laser

All-inorganic perovskite materials have been widely used in various devices, including lasers, light-emitting diodes (LEDs), and solar cells, due to their exceptional optoelectronic properties. Devices utilizing high-quality single crystals are anticipated to achieve significantly enhanced performance. In this work, we present a high-performance vertical cavity surface emitting laser (VCSEL) based on a single-crystal CsPbBr3 microplatelet, fabricated through a simple solution process and sandwiched between two distributed Bragg reflector (DBRs). The VCSEL demonstrated single-mode lasing at 542 nm, a low threshold of 5 µJ/cm2, and a high Q-factor of 2893. Additionally, time-resolved photoluminescence (TRPL) measurements using a streak camera revealed picosecond-scale lasing dynamics. This study offers a novel, to the best of our knowledge, approach for realizing laser devices using perovskite single-crystal microplatelets.

Lateral Phase Heterojunction for Perovskite Microoptoelectronics

Perovskite heterojunction engineering is the prerequisite but still a deficiency in the fabrication of micro-optoelectronic devices, where the present top-down or bottom-up techniques mainly focus on preparing the vertical heterojunction stacks. Perovskite lateral heterojunction structures generally rely on epitaxial growth, which cannot meet the demands of mass production of micro-devices. Here, a contact diffusion lithography technique is proposed to demonstrate a perovskite lateral phase heterojunction (LPH) polycrystalline film by ion-driven local phase transition. Under the guidance of thermodynamic simulations, methylamine contact and migration collectively promote in situ formation of α-phase formamidine-based perovskite patterns surrounded by δ-phase polymorphs. Spontaneous type-I heterojunction alignment between α- and δ-phases establishes energy funnels in the LPH film to facilitate carrier utilization and radiative recombination. The wide-bandgap δ-phase also serves as the coplanar isolator to achieve local anti-leakage for device integration. Based on the bright and stable LPH pattern layer, the near-infrared microscale perovskite light-emitting diode (micro-PeLED) with impressive device performance is achieved by following conventional device fabrication protocol. The proposed LPH enriches the perovskite heterojunction family, creates a new optoelectronic processing platform, and advances its versatile applications in micro-optoelectronics and photonics.

Perovskite Quantum Dots Lasing in Double-Heterostructure through Energy Transfer

Planar double heterostructures were initially investigated and have been successfully applied in III-V semiconductor lasers due to their excellent roles in confining both the photons and carriers. Here, we design and fabricate a (PEA)2Csn-1PbnX3n+1 (quasi-2D)/CsPbBr3 QD/quasi-2D double-heterostructure sandwiched in a 3/2 λ DBR microcavity, and then demonstrate a single-mode pure-green lasing with a threshold of 53.7 μJ/cm2 under nanosecond-pulsed optical pumping. The thresholds of these heterostructure devices decrease statistically by about 50% compared to the control group with no energy donor layers, PMMA/QD/PMMA in an identical microcavity. We show that there is efficient energy transfer from the barrier regions of the quasi-2D phases to the QD layer by transient absorption and luminescence lifetime spectra and that such energy transfer leads to marked threshold reduction. This work indicates that the double-heterostructure configurations should play a significant role in the future perovskite electrically pumped laser.

Whispering gallery mode micro-lasing in CsPbI3 quantum dots coated on TiO2 microspherical resonating cavities

Whispering gallery mode (WGM) lasing in CsPbI₃ quantum dots (QDs) coated on TiO₂ spherical microcavities is demonstrated. The photoluminescence emission from a CsPbI₃-QDs gain medium strongly couples with a TiO₂ microspherical resonating optical cavity. Spontaneous emission in these microcavities switches to a stimulated emission above a distinct threshold point of 708.7 W/cm². Lasing intensity increases three to four times as the power density increases by one order of magnitude beyond the threshold point when the microcavities are excited with a 632-nm laser. WGM microlasing with quality factors as high as Q∼1195 is demonstrated at room temperature. Quality factors are found to be higher for smaller TiO₂ microcavities (∼2 µm). CsPbI₃-QDs/TiO₂ microcavities are also found to be photostable even after continuous laser excitation for 75 minutes. The CsPbI₃-QDs/TiO₂ microspheres are promising as WGM-based tunable microlasers.

Dynamic manipulation of WGM lasing by tailoring the coupling strength

Miniaturized lasing with dynamic manipulation is critical to the performance of compact and versatile photonic devices. However, it is still a challenge to manipulate the whispering gallery mode lasing modes dynamically. Here, we design the quasi-three-dimensional coupled cavity by a micromanipulation technique. The coupled cavity consists of two intersection polymer microfibers. The mode selection mechanism is demonstrated experimentally and theoretically in the coupled microfiber cavity. Dynamic manipulation from multiple modes to single-mode lasing is achieved by controlling the coupling strength, which can be quantitatively controlled by changing the coupling angle or the coupling distance. Our work provides a flexible alternative for the lasing mode modulation in the on-chip photonic integration.

Directional Lasing from Nanopatterned Halide Perovskite Nanowire

Halide perovskite nanowire-based lasers have become a powerful tool for modern nanophotonics, being deeply subwavelength in cross-section and demonstrating low-threshold lasing within the whole visible spectral range owing to the huge gain of material even at room temperature. However, their emission directivity remains poorly controlled because of the efficient outcoupling of radiation through their subwavelength facets working as pointlike light sources. Here, we achieve directional lasing from a single perovskite CsPbBr₃ nanowire by imprinting a nanograting on its surface, which provides stimulated emission outcoupling to its vertical direction with a divergence angle around 2°. The nanopatterning is carried out by the high-throughput laser ablation method, which preserves the luminescent properties of the material that is typically deteriorated after processing via conventional lithographic approaches. Moreover, nanopatterning of the perovskite nanowire is found to decrease the number of the lasing modes with a 2-fold increase of the quality factor of the remaining modes.

Lithographic in-mold patterning for CsPbBr3 nanocrystals distributed Bragg reflector single-mode laser

Extensive studies on lead halide perovskites have shown that these materials are excellent candidates as gain mediums. Recently, many efforts have been made to incorporate perovskite lasers in integrated optical circuits. Possible solutions would be to utilize standard lithography with an etching/lift-off process or a direct laser etching technique. However, due to the fragile nature of the lead halide perovskites which gives rise to significant material deterioration during the lithography and etching processes, realizing a small-size, low-roughness, and single-mode laser remains a challenge. Here, a lithographic in-mold patterning method realized by nanocrystal concentration control and a multi-step filling-drying process is proposed to demonstrate CsPbBr₃ nanocrystals distributed-Bragg-reflector (DBR) waveguide lasers. This method realizes the patterning of the CsPbBr₃ nanocrystal laser cavity and DBR grating without lift-off and etching processes, and the smallest fabricated structures are obtained in a few hundred nanometers. The single-mode lasing is demonstrated at room temperature with a threshold of 23.5 μJ cm^-2. The smallest full width at half maximum FWHM of the laser output is 0.4 nm. Due to the fabrication process and the DBR laser geometry, the lasers can be fabricated in a compact array, which is important for incorporating perovskite-based lasers in complex optoelectronic circuits.