Highly Luminescent Gradient Alloy CdSe1-xSx Nanoplatelets with Reduced Reabsorption for White-Light Generation

Colloidal semiconductor nanoparticles have a great potential for designing high-quality white-light-emitting diodes (WLEDs). However, the nanoparticles suffer from the reabsorption effect due to the characteristic small Stokes-shifts, which limits the power conversion efficiency of the light sources. In order to resolve this problem, absorption and emission spectra of the nanoparticles should be separated. Here, we report on gradient alloy CdSe1-xSx nanoplatelets (NPLs), which allow for suppression of the reabsorption. Thanks to the gradient composition, the S-rich domains of CdSe1-xSx NPLs behave as an efficient antenna, adsorbing light and funneling the generated carriers into the Se-rich domains, where they recombine. The gradient structure of CdSe1-xSx NPLs allows one to control the overlap of the emission and absorption spectra simply by varying their composition. By controlling the composition of CdSe1-xSx NPLs, their photometric parameters, including chromaticity color coordinates, color rendering index (CRI), and correlated color temperature (CCT), can be tuned. Due to the wide trap-assisted emissions associated with unsaturated S/Se surface atoms, CdSe1-xSx NPLs demonstrate exceptionally high CRI values ranging from 87 up to 94 at CCT values in the range of 2509-6448 K, making them promising for high-quality white-light generation. Finally, WLEDs based on as-obtained gradient alloy CdSe1-xSx NPLs are fabricated that show high luminous efficiencies (LE) reaching values up to 250 lm/W and CRI values as high as 91, demonstrating their potential for commercial applications.