Highly Luminescent Gradient Alloy CdSe_1–xS_x Nanoplatelets with Reduced Reabsorption for White-Light Generation

Abstract

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 CdSe 1−x S x nanoplatelets (NPLs), which allow for suppression of the reabsorption. Thanks to the gradient composition, the S-rich domains of CdSe 1−x S x 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 CdSe 1−x S x NPLs allows one to control the overlap of the emission and absorption spectra simply by varying their composition. By controlling the composition of CdSe 1−x S x 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, CdSe 1−x S x 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 CdSe 1−x S x 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.

Hole Transfer Dynamics of 2D CdSeS Alloy Nanoplatelets for Photon-to-Current Conversion

“…The XRD pattern depicts the reflections of (111), (200), (220), (311), and (400) peaks at 2θ angles of 25.36°, 29.71°, 41.88°, 49.86°, and 60.97°, respectively, indicating the presence of a major zinc blende (ZB) structure in alloy NPLs (Figure a) . The reflection for alloy NPLs shifts toward the higher angle, compared to the CdSe NPLs after incorporation of S 2– ion in place of Se 2– ion in alloy NPLs . The morphology of the 2D 4-ML CdSeS alloy NPLs is investigated using transmission electron microscopy (TEM).…”

“…The crystalline structure of the alloy NPLs is investigated from thin-film X-ray diffraction (XRD) study. The XRD pattern depicts the reflections of (111), (200), (220), (311), and (400) peaks at 2θ angles of 25.36°, 29.71°, 41.88°, 49.86°, and 60.97°, respectively, indicating the presence of a major zinc blende (ZB) structure in alloy NPLs (Figure a) . The reflection for alloy NPLs shifts toward the higher angle, compared to the CdSe NPLs after incorporation of S 2– ion in place of Se 2– ion in alloy NPLs .…”

“…28 The reflection for alloy NPLs shifts toward the higher angle, compared to the CdSe NPLs after incorporation of S 2− ion in place of Se 2− ion in alloy NPLs. 28 The morphology of the 2D 4-ML CdSeS alloy NPLs is investigated using transmission electron microscopy (TEM). The top-view TEM images of NPLs are rectangular where some NPLs are lying flat on their basal plane and some are standing on their edges (Figure 1b).…”

“…Vasiliev et al have introduced another highly luminescent gradient alloy CdSe 1– x S x NPLs to control the overlap of absorption and emission by varying the sulfur composition. Here, the S-rich domain acts as an efficient antenna to absorb the light and funnel the generated charge carriers to the Se-rich domain for recombination . Apart from the tuning of optical properties, lattice strain and structural defects can be modulated by alloying, which further influences the carrier dynamics as well .…”

“…Here, the S-rich domain acts as an efficient antenna to absorb the light and funnel the generated charge carriers to the Se-rich domain for recombination. 28 Apart from the tuning of optical properties, lattice strain and structural defects can be modulated by alloying, which further influences the carrier dynamics as well. 29 Zhang et al have reported the surface defect trapping of charge carriers in CdS x Se 1−x alloy nanobelts that facilitates enhanced photoconductivity in nanobelts-based optoelectronic devices.…”