Hot-carrier trapping preserves high quantum yields but limits optical gain in InP-based quantum dots

TL;DR

InP-based quantum dots exhibit ultrafast hot-carrier trapping that limits their optical gain potential despite maintaining high quantum yields, contrasting with other quantum dot materials.

Contribution

This study reveals the unique hot-carrier trapping dynamics in InP quantum dots that hinder their use as gain media, a phenomenon not observed in other quantum dot materials.

Findings

Hot-carrier trapping occurs within femtoseconds to microseconds.

InP quantum dots maintain brightness but cannot achieve population inversion.

Compared to other quantum dots, InP shows distinct hot-carrier dynamics.

Abstract

Indium phosphide is the leading material for commercial applications of colloidal quantum dots. To date, however, the community has failed to achieve successful operation under strong excitation conditions, contrasting sharply with other materials. Here, we report how the unusual photophysics of state-of-the-art InP-based quantum dots make them unattractive as a gain material. A combination of ensemble-based time-resolved spectroscopy over timescales from femtoseconds to microseconds and single-quantum-dot spectroscopy reveals ultrafast trapping of hot charge carriers. This process leads to charge-carrier losses, thereby reducing the achievable population inversion which limits amplification of light in a gain material. Interestingly, fluorescence is only delayed, not quenched, by hot charge-carrier trapping, explaining why InP-based quantum dots are successful as bright luminescent colour convertors for low-intensity applications. Comparison with other popular quantum-dot materials, such as CdSe, Pb-halide perovskites, and CuInS2, indicate that the hot-carrier dynamics observed are unique to InP.