title: Whispering gallery mode lasing from hexagonal shaped layered lead iodide crystals.
abstract: We report on the synthesis and optical gain properties of regularly shaped lead iodide (PbI2) platelets with thickness ranging from 10-500 nm synthesized by chemical vapor deposition methods. The as-prepared single crystalline platelets exhibit a near band edge emission of ∼ 500 nm. Whispering gallery mode (WGM) lasing from individual hexagonal shaped PbI2 platelets is demonstrated in the temperature-range of 77-210 K, where the lasing modes are supported by platelets as thin as 45 nm. The finite-difference time-domain simulation and the edge-length dependent threshold confirm the planar WGM lasing mechanism in such hexagonal shaped PbI2 platelet. Through a comprehensive study of power-dependent photoluminescence (PL) and time-resolved PL spectroscopy, we ascribe the WGM lasing to be biexcitonic in nature. Moreover, for different thicknesses of platelet, the lowest lasing threshold occurs in platelets of ∼ 120 nm, which attributes to the formation of a good Fabry-Pérot resonance cavity in the vertical direction between the top and bottom platelet surfaces that enhances the reflection. Our present study demonstrates the feasibility of planar light sources based on layered semiconductor materials and that their thickness-dependent threshold characteristic is beneficial for the optimization of layered material based optoelectronic devices.
authors.affiliation: Division of Physics and Applied Physics, School of Physical and Mathematical Sciences, Nanyang Technological University , Singapore 637371, Singapore.
authors.forename: Xinfeng
authors.initials: X
authors.lastname: Liu
authors.forename: Son Tung
authors.initials: ST
authors.lastname: Ha
authors.forename: Qing
authors.initials: Q
authors.lastname: Zhang
authors.forename: Maria
authors.initials: M
authors.lastname: de la Mata
authors.forename: César
authors.initials: C
authors.lastname: Magen
authors.forename: Jordi
authors.initials: J
authors.lastname: Arbiol
authors.forename: Tze Chien
authors.initials: TC
authors.lastname: Sum
authors.forename: Qihua
authors.initials: Q
authors.lastname: Xiong
keywords: Fabry−Pérot cavity; hexagonal platelet; lasing; layered materials; lead iodide; whispering gallery mode (WGM)