Comparisons of the structural and optical properties of o-AgInS2, t-AgInS2, and c-AgIn5S8nanocrystals and their solid-solution nanocrystals with ZnS

Abstract

Cubic AgIn₅S₈ (c-AgIn₅S₈) as well as orthorhombic AgInS₂ (o-AgInS₂) and tetragonal AgInS₂ (t-AgInS₂) nanocrystal (NC) luminophores are successfully prepared by adjusting the stoichiometric [Ag] : [In] ratio at reaction temperatures ranging from 100 to 180 °C. The photoluminescence (PL) quantum yield (QY) of c-AgIn₅S₈ NCs reached 18.8%, which is much higher than that of o-AgInS₂ and t-AgInS₂. In this study, the identification and characterization of efficient c-AgIn₅S₈ luminophore NCs are reported for the first time. Broad PL bands, large Stokes shifts and long PL lifetimes indicate that the PL of c-AgIn₅S₈ as well as o-AgInS₂ and t-AgInS₂ NCs can be attributed to donor–acceptor (D–A) pair recombinations. The PL peak shifts and changes in the PL intensity depending on the excitation intensity and temperature confirm that the c-AgIn₅S₈ NCs comply with D–A pair recombinations. The PL emission of the NCs can be enhanced via a solid-solution with ZnS and the PL wavelength can be tuned by varying the stoichiometric [Ag] : [In] ratio and the preparation temperature. The best c-AgIn₅S₈–ZnS sample presents a PL emission in the range of 552–587 nm with a maximum QY of 61.3%. The luminous efficacy and color rendering index (CRI) of these AgIn₅S₈–ZnS NC-based white light-emitting diodes (LEDs) were respectively 53 lm W⁻¹ and 74 at 3700 K under 60 mA. The development of an efficient AgIn₅S₈–ZnS NC to be applied as a color-converting material in white LEDs as demonstrated in this work provides the possibility of various potential applications in the fields of optic, optoelectronic and bio-related devices.