Synthesis And Characterization Of Niobate-Based Red-Emitting Phosphors For White LED Application

White-light LED (Light Emitting Diode) is known as the fourth generation solid-state lighting for substituting the incandescent lamps and fluorescent lamps, and the most valuable light source in the21st century, because of such advantages as environment protection, long service life, short response time, high energy efficiency, high reliability, uncomplicated framework, light in weight, low-voltage and safety. Therefore, white-light LED presents a more promising and wider application. However, at present, the lack of the high-efficiency, high-stability red-emitting phosphors, which can be excited effectively by the near-UV and blue light, results in the lower color rendering index of white-light LED and hinders the further development of white-light LED technologies to large extent.The structures of host materials have significant influence on the properties luminescent materials. Niobates possessing multiple structure forms are an important source in search for photo-activated host materials for high performance white-light LED phosphors owe to their excellent thermal and chemical stability. In the third chapter of the dissertation, fluorite-structured RE3NbO7(RE=Y. La. Gd) are selected as host materials, and solid phase synthesis and luminescent properties of Eu3+doped RE3NbO7are studied for the first time. The effects of doped amount of Eu3+. annealing temperature, sort of fluxes and co-doped alkali metal ions on the phase, morphology, and luminescent properties of the products are systematically investigated and the relevant mechanisms are also discussed. The results show that fluorite-structured Y2.5NbO7:0.5Eu3-phosphors can be obtained after5-hour annealing at1300℃using5wt.%Li2SO4·H2O as flux that Y2.5NbO7:0.5Eu3+. which shows intense red emission at617nm under excitation of near UV light at396nm. In comparison with the commercial Y2O2S:Eu3+and the investigated Y0.75NbO4:0.25Eu3+. the fluorite-structured Y2.5NbO7:0.5Eu3+could be considered as a novel and high performance red-emitting phosphor for promising application to near UV InGaN-based LED solid-state lighting.Aiming at the problems existing in synthetic strategies for niobate-based phosphors, such as high-temperature and long-duration calcination, large and uneven particle size and irregular morphology, etc., a novel route to synthesize RENbO4:Eu3+via a salt-assisted solution combustion process has been proposed. The effects of sorts of assistant salts (Li2SO4·H2O, KF, NaCl) and annealing temperature on the phase, morphology, and luminescent properties of the products are systematically investigated and the relevant mechanisms are also discussed. The results show that the pure phase RENbO4:Eu3+phosphors can be prepared in one step by introducing Li2SO4·H2O using as flux and NH4NO3using as oxidant into the precursor mixture for combustion reaction. The RENbO4:Eu3+phosphor obtained after annealing the salt-containing combustion-derived products at1000℃for2h shows an increase in relative intensity of Eu3+(5D0â†'7F2) emission by a factor of1-3compared with the RENbO4:Eu3+phosphors synthesized by high temperature solid phase method (1300℃for2h). Moreover, the phosphor particles prepared via a salt-assisted solution combustion process are regular in shape, smooth in surface, uniform in size and well-dispersed.