Highly luminescent air-stable AgInS2/ZnS core/shell nanocrystals for grow lights

Abstract

Plants need lights in the blue (400–500 nm) and red (600–700 nm) spectral regions for the photosynthesis to grow. Lights to match the mentioned spectral ranges can be provided from a blue LED and red luminescence materials. This article presents the high yield solvothermal syntheses of AgInS2 (AIS) core nanocrystals (NCs) and AIS/ZnS core/shell NCs that emit stably strong luminescence peaking around 665 nm under the excitation of a blue LED. The solvothermal syntheses of AIS core NCs were performed in oleylamine solvent added with 1,3-dimethylthiourea at 200 °C for a relatively short time of 20 min, in a closed Teflon vessel. Then, the ZnS shells with different thicknesses of 1, 3, 5, and 7 monolayers were coated on the same AIS core NCs at 150 °C for 60 min under open air. The synthesised AIS core and AIS/ZnS core/shell NCs were characterised by using X-ray diffraction (XRD), transmission electron microscopy (TEM), and optical spectroscopies (UV–Vis absorption and photoluminescence (PL), including steady state and time-resolved PL). With increasing the thickness of the ZnS shell, AIS/ZnS core/shell NCs become more stable under open air to emit the strong luminescence in the 600–700 nm range, peaking at ∼650 nm with the high luminescence quantum yield (QY) up to ∼60%. The blue-shift of the emission and increase of the QY after shelling AIS core NCs with ZnS are rationalized by the formation of the partially alloyed structure and passivation of surface states. In addition, time-resolved PL spectra exhibit to be red-shifted with the delay time after the excitation that is evident for the nature of donor–acceptor pairs recombination in AIS/ZnS core/shell NCs. Coating of layers of AIS/ZnS core/shell NCs dispersed in transparent epoxy on the 460-nm LED as assays for the grow light sources are also illustrated.