Synthesis And Optical Properties Of BaMoO₄: Pr³⁺ Phosphor System For White LED Application

A highly efficient red phosphor, BaMoO4:Pr3+, has been fabricated by a convenient method and we researched the influence of optical properties by doping alkali metals and halide in the phosphor system BaMoO4:Pr3+. We also prepared BaMoO4:Pr3+/Na+ hollow microspheres composed of nanocrystals by a solution chemistry method without adding any templates. In addition,the structures, morphologies and optical properties of as-prepared products were thoroughly characterized by using TG-DTA, XRD, XPS, BET, SEM, FESEM, TEM, HRTEM), and PL, respectively. The main results are summarized as follows:BaMoO4:Pr3+ phosphors were synthesized successfully by a convenient solid method via annealing at 900°C. The sizes of as-prepared particles are below 3μm and a strong red emission band centered at 643nm corresponding to the transition 3P0→3F2 of Pr3+ is observed under 430-500 nm excitation. The emission intensity of red phosphor BaMoO4: Pr3+ is 5.6 times compared with that of the commercial red phosphor Y2O2S:Eu3+. And the materials have the stable physical and chemical properties and high luminous efficiency. Furthermore, the material method is simple and the raw materials are low cost, fully suitable for industrial production. The color rendering will be improved significantly when the materials applied in white LEDs. The introduce of alkali metal and halide in the phosphor system BaMoO4:Pr3+ and the alkali metal and halide co-doped phosphors were prepared by adding appropriate amounts of alkali halide into the mixtures of BaCO3, (NH4)6Mo7O24·4H2O and Pr6O11.The doping alkali metal and halide can play an important role in balancing the charge in the materials. The red emission intensity was enhanced significantly by doping alkali metal and halide in the BaMoO4:Pr3+ phosphor system and the emission intensity is 2.67 times compared with that of undoped alkali metal and halide samples. In addition, we checked the temperature dependence of the emission intensity of samples. Experimental results showed that the red emission intensity of Ba0.96MoO4:0.02Pr3+,0.02KCl remained about 74% at 150°C which met the temperature quenching indicators of phosphors for white LED application in the market.In addition, we prepared BaMoO4:Pr3+/Na+ hollow microspheres composed of nanocrystals by a solution chemistry method without adding any templates. The average size of hollow mirospheres was 3-5μm and the hollow mirospheres composed by nanocrystals well-dispersed with a 30-60 nm size. The nanocrystals with extraordinarily high crystallinity produce excellent luminescence emission. The small amount of Na+ ions in BaMoO4:Pr3+ hollow mirospheres can play a role in charge balance and improve the optical properties of the materials. The paper discussed the growth mechanism of the hollow structured BaMoO4:Pr3+/Na+ microspheres. We explained the growth mechanism by Ostwald ripening and put forward that citric acid played a key role in the formation process of hollow microspheres composed of nanocrystals.Furthermore, the self-assembly concept may also be applicable to other compounds for design and fabrication of novel functional nanoarchitectures.