Reducing the Chromaticity Shifts of Light-Emitting Diodes Using Gradient-Alloyed Cd _x Zn _{1− x} Se _y S _{1− y} @ZnS Core Shell Quantum Dots with Enhanced High-Temperature Photoluminescence

Gradient-alloyed Cd _x Zn _{1− x} Se _y S _{1− y} @ZnS core shell quantum dots are the most popular materials used in light-emitting diodes for liquid crystal display backlights. High-temperature photoluminescence is an essential property in determining the chromaticity shifts of on-chip type devices. In this work, the photoluminescence quenching effect of Cd _x Zn _{1− x} Se _y S _{1− y} @ZnS quantum dots is investigated by measuring the steady and time-resolved PL spectra at elevated temperatures. The thermal quenching of Cd _x Zn _{1− x} Se _y S _{1− y} @ZnS quantum dots can be explained by a thermally activated physical process, including electron resonance tunneling into pre-existing surface trap states, injection over the barrier energy back to the core, and recombination with the confined holes. By combing the theoretical analysis and experimental results, the influence of core composition and shell thickness of Cd _x Zn _{1− x} Se _y S _{1− y} @ZnS QDs on the quenching effect is illustrated. It is found that the integrated photoluminescence intensity of ZnSe-rich quantum dots with 20 monolayers ZnS shell at 500 K can reserve 85.1%, relative to the value at 300 K. Quantum dots with enhanced photoluminescence emission at high temperature enable the fabrication of light-emitting diodes with reduced chromaticity shifts.