Molecular beam epitaxy of two-dimensional (2D) GaTe nanostructures on GaAs(001) substrates has been reported in this study. A trade-off between growth temperature and growth time (thickness) is a prerequisite for governing the crystal morphology of 2D GaTe materials from 2D epitaxial thin films to pseudo-one-dimensional (1D)/2D nanostructures (including nanorods, nanotriangles, and nanodendrites). Importantly, through real-time azimuthal reflection high-energy electron diffraction, a coexistence of hexagonal-GaTe (h-GaTe) and monoclinic-GaTe (m-GaTe) phases in the film was explored, corresponding to formation of lateral h/m-GaTe heterophase homojunctions. In addition, we found that utilizing a GaN/sapphire platform instead of the GaAs(001) substrate promotes formation of a single-phase h-GaTe in the thin film, which could be due to the surface-symmetry matching between the GaN/sapphire platform and the h-GaTe phase. Together with observing an asymmetric emission broad band of ∼1.76 eV that comes from the pseudo-1D m-GaTe phase, we provide convincing evidence that the emission feature located at 1.46 eV originates from the near-band-edge emission of the 2D h-GaTe epitaxial thin film. These results are meaningful in providing practical schemes to control the crystal phases of 2D GaTe materials and realize either hexagonal–monoclinic heterophase lateral homojunctions or single-phase h-GaTe epitaxial thin films on a wafer scale for future functional (opto)electronic devices, especially for near-infrared photodetectors.
A series of Mn4+-activated CaAl2O4 (CAO) compounds were synthesized by co-precipitation to seek a candidate for a red-emitting phosphor to be employed in a white LED. The crystal structure, morphology, and fluorescence properties of the as-obtained phosphors were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), and photoluminescence (PL). The deep red luminescence of Mn4+ in CaAl2O4 is reported and discussed. The excitation spectrum exhibited broadband emission between 260 and 550 nm with three peaks dominating at 320 nm due to the transition of 4A24T1. Theemission spectra between 600 to 720 nm displays an overwhelming emission peak at 654 nm owing to the 2E4A2 transition of Mn4+ ion.This research demonstrates the great promise of CaAl2O4:Mn4+ as a commercial red phosphor in warm white LEDs and opens up new avenues for the exploration of novel non-rare-earth red-emitting phosphors.
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