Enhancement of Two-Photon Fluorescence and Low Threshold Amplification of Spontaneous Emission of Zn-processed CuInS₂ Quantum Dots

Heavy-metal-free I–III–VI₂ quantum dots (QDs) have recently emerged as favorable alternatives to toxic II–VI QDs for optoelectronic and biological applications, but low fluorescence efficiency is a key issue related to the promising nanocrystals. In this work, we demonstrate big enhancement of two-photon fluorescence efficiency and low threshold two-photon pumped amplification of spontaneous emission (ASE) of Zn-processed CuInS₂ (CIS) QDs for the first time. The change of two-photon process caused by Zn²⁺ cation exchange in CIS QDs is systematically investigated. Two-photon ASE in Zn-processed CIS QDs films is achieved with a record of low threshold fluence of 5.7 μJ/cm². With high two-photon fluorescence quantum yields and low threshold ASE, the Zn-processed CIS QDs could become a promising candidate for two-photon bioimaging, nonlinear optical and novel QDs laser devices.