Synthesis, growth mechanism and optical properties of YBO3-based LEDs phosphors
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A family of monodisperse YBO3: Eu3+ 3D microstructure with nine morphologies were firstly synthesized under hydrothermal conditions. Different microstructures were controllably obtained through adjusting the molar ratio of Y: B (Yttrium: Boron) and solvent. Photoluminescence (PL) of nine samples were investigated and demonstrated that under the excitation of 254 and 363 nm honeycomb-like YBO3: Eu3+ spheres had the highest Red/Orange ratio as potential red phosphor for applications, such as PDPs (plasma display panels) and LEDs (light emitting diodes). Subsequently, the morphology of YBO3: Eu3+ is further controlled by changing the borate starting material and pH values. Moreover, related photoluminescence of YBO3: Eu3+ with various morphologies was compared. There is the graduate increase of luminescence intensity of Eu3+ on annealing the YBO3: Eu3+ microflowers at 400, 600, and 800 °C. The growth process of the YBO3 sparse and dense flowers was explored based on the time-dependent experiments and the results showed that the growth mechanism follows an in-situ growth through an initial nucleating, localized self-assembly, and Ostwald ripening process rather than self-assembly process as reported previously. Photoluminescence of white LEDs phosphors YBO3: Tb3+, Eu3+ was systematically studied demonstrating that under the excitation of 365 nm ultraviolet (UV) light. Tunable emission by varying the relative doping ratios were demonstrated, and eventually YBO3: Tb3+ (12.5%), Eu3+ (2.5%) exhibits a white light. It includes three emissions: a blue band attributed to self-trapped exciton, a green band due to the Tb3+ transition of 5D4 −7Fj (j = 6, 5, 4, 3), and a red band due to the Eu3+ transition of 5D0 −7Fj (j = 0, 1, 2, 3, 4). Energy transfers from host YBO3 to Tb3+, and Eu3+ and Tb3+ to Eu3+, as well as tunable emission by varying the relative doping ratios were identified through experimental strategies. At last, the combination of blue emission from self-trapped exciton with green and red emissions from activators was firstly used to fabricate white light emitting diodes by coating YBO3: Tb3+ (12.5%), Eu3+ (2.5%) phosphors on the commercial UVLED. Corresponding CIE coordinate, electroluminescence, color temperature, luminous efficiency, etc. were measured for the assessment of application.