Fig. 2: Optical characteristics of ZnS/GaP QS.

a STEM image showing (i) ZnS core and ZnS/GaP QSs synthesized at temperatures of (ii) 200 °C, (iii) 250 °C, and (iv) 300 °C (scale bar: 20 nm). The inset displays a high-resolution TEM image (scale bar: 5 nm). b Particle size histograms fitted with Gaussian curves, based on the STEM images. c Quantitative analysis of the Ga-to-P ratio relative to the Zn-to-S ratio, as a function of GaP shell formation temperature, obtained using ICP-MS. d Absorption spectra of ZnS core and ZnS/GaP QSs as a function of GaP shell formation temperature. The dotted line and circle indicate the absorption shoulder of ZnS core. e Absorption spectra as a function of GaP shell formation time. The inset in (e) displays the photoluminescence (PL) spectra for each sample. The inset PL spectra are also shown in the Supplementary Fig. 4c(ii). f PL spectra of ZnS/GaP QSs, measured as a function of GaP shell formation temperature. g Photoluminescence quantum yield (PLQY) of ZnS/GaP QSs as a function of both GaP shell formation time and temperature. h Absorption spectra of ZnS/GaP QSs as a function of ZnS core conditions. Unless otherwise noted, the default synthesis conditions for the ZnS cores are 260 °C for 60 min, and for the GaP shells, 250 °C and a synthesis time of 60 min.