Photoluminescent Cd_xZn_1–xS/CdSe/Cd_yZn_1–yS Core/Shell Quantum Dots of Varying Shell Thicknesses for White Light-Emitting Diodes

Designing a type-I core–shell structure with a shell thickness of >5 nm is the best approach for achieving highly luminescent and stable colloidal quantum dots (QDs). Investigating the temperature-dependent photoluminescence (PL) spectra of these QDs with varying shell thicknesses will help us gain a deeper understanding of how shell thickness influences their diverse optical properties. In this study, we systematically synthesized highly luminescent red- and green-emitting Cd x Zn 1– x S/CdSe/Cd y Zn 1– y S QDs with coherent strained well-type structures featuring varying shell thicknesses. Then, three shell thicknesses of red- and green-emitting QDs with comparable luminescence properties are selected to investigate their photoluminescence properties under temperatures from 80 to 431 K. We find that as the temperature increases, the spectral redshift, broadening, and intensity reduction of the QDs caused by phonon participation are inverse to the shell thickness. Fitting results reveal that a thicker shell weakens electron(exciton)-phonon coupling and increases the exciton binding energy of QDs by isolating the photogenerated excitons away from the inorganic–organic interface. This enables the QDs with a thicker shell to exhibit excellent luminescence efficiency and thermal stability, as evidenced by the stability performance (under varied currents and long-term operation) of photoluminescence white light-emitting diodes based on red- and green-emitting QDs with three different shell thicknesses. Our findings offer an alternative interpretation of the shell thickness-dependent photoluminescence properties of QDs.