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-upassembly 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 $Cd_xZn_{1-x}S$ shell with a nominal size of 14 × 15 × 4.2 nm, and CQDs of $CdS_xSe_{1-x}/ZnS$with 6 nm diameter. SPs areoptically characterized with a 0.76 ns pulse laser (spot size: 2.88 × 10$^{−7}$ cm$^2$ )at 532 nm, and emit in the 620–670 nm spectral range. Results show thatCQW 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 CQDSPs. 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.