Highly luminescent near-infrared Cu-doped InP quantum dots with a Zn–Cu–In–S/ZnS double shell scheme

Abstract

Upon Cu doping into host semiconductor quantum dots (QDs), intra-gap states inside the band gap are generated, by which energy down-shifted photoluminescence (PL) with broad emissivity and large Stokes shift emerges. Technologically important, environmentally friendly InP QDs typically used as green and red emitters in display devices can achieve exceptional PL quantum yields (QYs) of near-unity (95–100%) when the-state-of-the-art core/shell heterostructure of the ZnSe inner/ZnS outer shell is elaborately applied. Meanwhile, the PL QYs of red-to-near-infrared (IR)-emitting Cu-doped InP (InP:Cu) QDs reported to date are still modest (40–58%). Herein, we explore the synthesis of strain-engineered highly emissive InP:Cu/Zn–Cu–In–S (ZCIS)/ZnS core/shell/shell QDs via a one-pot approach. When this unconventional combination of a ZCIS/ZnS double shelling scheme is introduced to a series of InP:Cu cores with different sizes, the resulting InP:Cu/ZCIS/ZnS QDs with a tunable near-IR PL range of 694–850 nm yield the highest-ever PL QYs of 71.5–82.4%. These outcomes strongly point to the efficacy of the ZCIS interlayer, which makes the core/shell interfacial strain effectively alleviated, toward high emissivity. The presence of such an intermediate ZCIS layer is further examined by comparative size, structural, and compositional analyses.