Colloidal Semiconductor Quantum Well Supraparticles as Low-Threshold and Photostable Microlasers

Abstract

This study introduces and compares the lasing performance of micron-sized and sphere-shaped supraparticle (SP) lasers fabricated through bottom-up assembly of II-VI semiconductor colloidal quantum wells (CQWs) with their counterparts made of quantum dots (CQDs). CQWs consist of a 4-monolayers thick CdSe core and an 8-monolayers thick Cd_xZn_1-xS shell with a nominal size of 14 × 15 × 4.2 nm, and CQDs of CdS_xSe_1-x/ZnS with 6 nm diameter. SPs are optically characterized with a 0.76 ns pulse laser (spot size: 2.88 × 10⁻⁷ cm²) at 532 nm, and emit in the 620–670 nm spectral range. Results show that CQW SPs have lasing thresholds twice as low (0.1–0.3 nJ) as CQD SPs (0.3–0.6 nJ), and stress tests using a constant 0.6 nJ optical pump energy demonstrate that CQW SPs withstand lasing emission for longer than CQD SPs. Lasing emission in CQW and CQD SPs under continuous operation yields half-lives of τ_CQW SP ≈150 min and τ_CQD SP ≈22 min, respectively. The half-life of CQW SPs is further extended to τ_QW ≈385 min when optically pumped at 0.5 nJ. Such results compare favorably to those in the literature and highlight the performance of CdSe-based CQW SPs for laser applications.