Synthesis And Characterization Of Red-Emitting Phosphors For White LED Via A Salt-Assisted Spray Combustion Process

Due to their long life-span, low energy consume, low quality of heat and short response time, white LEDs are commonly considered as the most valuable light source in the21st century. However, at present, the high-efficiency, high-stability red-emitting phosphors, which can be excited effectively by the near-UV and blue light, are in urgent need. In the recent years, niobate-based and molybdate-based red-emitting phosphors have been the research focus in search for the high-performance phosphors promising in white LED lightening, but so far there have not been synthesized via a solution combustion process. Aiming at the problems existing in synthetic strategies for niobate-based and molybdate-based phosphors, such as large and uneven particle size and irregular morphology, etc. Resulting from precipitation prior to ignition, selecting ZnMoO4:Eu3+, YNbO4:Eu3+and Y2.5NbO7:0.5Eu3+as objects to be synthesized, a novel synthetic approach via a salt-assisted spray combustion process has been proposed based on a salt-assisted spray combustion process combined with ultrasonic spray technology. In the dissertation, the effects of the sort and amount of assistant salts, amount of fuel, amount of ammonia nitrate, ignition temperature, annealing temperature, and precursor solution concentration, etc., on the phase, morphology and luminescent property of the products in the synthetic process are systematically investigated by X-ray diffraction (XRD), photoluminescence spectroscopy, scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The relevant mechanism is also discussed.The results show that by introducing such assistant salts as NaCl and Li2SO4into the precursor mixture for combustion reaction, not only can the pure phase Zn0.8MoO4:0.2Eu3+nanophosphors be prepared in one step at900℃,and Y0.95NbO44:0.05Eu3+submicron spheres be prepared in one step at1100℃when salt/Nb=1or the amount of NH4NO3is double stoichiometric, but also the Y2.5NbO7:0.5Eu3+superfine phosphors can be obtained after5-hour annealing of the products derived from spray combustion process at1100℃, which is far below the phase-forming temperature when adopting traditional solid phase method.The particles size of three phosphors of different structures are reduced when the salt is added.In summary, in the synthetic process of niobate-based and molybdate-based phosphors, the ultrasonic spray combustion synthetic approach can avoid the segregation and precipitation of the constitutes while the introduction of assistant salts into the precursor solution can promote the formation of the desired phase and effectively prevent the particles from agglomerating and sintering. Therefore, the approach is characterized by rapid synthesis, fine and well-dispersed particles, no/lower temperature annealing and energy-saving, and is expected to find wider application prospect in controlled preparation of superfine/nano-sized phosphors.