Synthesis of near-infrared-emitting type-II In(Zn)P/ZnTe (core/shell) quantum dots

Highlights: • Heavy metal-free near-Infrared-Emitting type-II In(Zn)P/ZnTe/ZnSeS (core/shell/shell) quantum dots are synthesized. • The type-II band engineering enables In(Zn)P/ZnTe quantum dots to emit at wavelengths that are beyond the visible region. • Emission range of the quantum dots can be tuned by varying the In(Zn)P core diameter and ZnTe shell thickness. • The ZnSeS outer shell allow surface modification while preserving the optical and chemical stabilities. -- Abstract: InP-based quantum dots (QDs) are considered promising candidates for replacing Cd-based QDs and ideal light emitters for next-generation displays. However, their spectral windows are confined to visible wavelengths, which restricts their applicability beyond displays. Thus, non-toxic colloidal QDs with the potential to extend the spectral window are highly desirable for many practical applications. Here, near-infrared-emitting type-II In(Zn)P/ZnTe (core/shell) QD heterostructures are fabricated. As the ZnTe shell grows on an In(Zn)P QD core, the absorption band redshifts owing to the decreased optical band gap. Near-infrared photoluminescent (PL) emission by type-II In(Zn)P/ZnTe (core/shell) QDs is realized by introducing an outer shell comprising ZnSeS passivation layers. The PL emission range of the resulting type-II In(Zn)P/ZnTe/ZnSeS (core/shell/shell) QDs can be tuned by varying the In(Zn)P core diameter and ZnTe shell thickness. Meanwhile, the proposed QDs also exhibit a prolonged exciton lifetime of 387 ns indicates the type-II characteristics. Moreover, the ZnSeS passivation layers enable surface modification while preserving the optical and chemical stabilities, resulting in water-soluble QDs. Importantly, heavy-metal-free near-infrared-emitting type-II In(Zn)P/ZnTe (core/shell) QDs have immense potential to increase the utilization of such materials in biomedical and energy applications requiring nontoxicity and near-infrared emission.