Low-threshold near-infrared lasing at room temperature using low-toxicity Ag2Se quantum dots

Abstract

The development of colloidal near-infrared quantum dot (QD) lasers has been hindered by the high state degeneracy of lead salt QDs. Here, we show that this challenge can be addressed by utilizing orthorhombic Ag₂Se QDs. We demonstrate that the lowest quantized states of Ag₂Se QDs display a low, 2-fold degeneracy by employing femtosecond transient absorption (TA) spectroscopy. The optical gain threshold is evaluated to be 156 μJ cm⁻², corresponding to ∼1.4 excitons per QD on average. Consequently, the amplified spontaneous emission (ASE) threshold of Ag₂Se QD films is as low as 183 μJ cm⁻². A large modal gain (∼470 cm⁻¹) of the film is observed by variable stripe length (VSL) measurements. We leverage the low-threshold gain of the QDs to produce microlasers that exhibit single-mode near-infrared emission and a low threshold of 163 μJ cm⁻² at room temperature. In addition, the cytotoxicity of Ag₂Se QDs is remarkably negligible. Our work represents a significant step toward environmental-friendly near-infrared QD lasers.