Optical Properties of Er3+-doped ZnO Nanocrystals Synthesized by Solid State Reaction Method

The ZnO:Er3+ is synthesized using a combination of the solid-state reaction method and a water bath heating process. The effect of Er3+ concentration and annealing temperature on the structure, morphology and optical properties of the samples is studied. X-ray diffraction (XRD) and scanning electron microscopy (SEM) studies show that the ZnO:Er nanoparticles have a hexagonal wurtzite structure with a spherical-like morphology, and the particle size of the sample with 3% Er3+ doped under 800°C annealing is approximately 70 nm. Compared with pure ZnO, the doping by Er3+ reduces the crystallite size and lattice parameters, and it also increases the dislocation density. The bandgap width of the 3% Er3+-doped ZnO nanoparticles annealed at 800°C is approximately 3.23 eV. The excitation peaks of the samples we prepared match those of commercial blue light chips (445–465 nm). The sample exhibited broadband emission in the range of 500–760 nm when excited at 451 and 493 nm. The most intense luminescence was observed for the 3% Er3+-doped sample annealed at 800°C, which yielded CIE 1931 chromaticity coordinates in the yellow region. The material exhibits white emission with CIE 1931 coordinates of (0.32, 0.39) and a Correlated Color Temperature (CCT) of 5825 K, suggesting potential in blue light-emitting diode (LED) phosphors, ultraviolet (UV) shielding, and full-color displays. The luminescence mechanism is also discussed.