Comparisons of the structural and optical properties of o-AgInS2, t-AgInS2, and c-AgIn5S8 nanocrystals 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.