Controllable Preparation And Characterization Of Rare Earth Doped Molybdates Luminescent Materials

White light emitting diodes (LEDs) as a new generation of solid-state light sourcedue to their excellent properties such as reliability, energy saving, high luminousefficiency and stability, long operating time, small volume and so on. Hence, WhiteLEDs shows an extensive application prospect in the display and efficient lightingmarket. As an important part of LEDs, to explore and research rare-earth dopedluminescent materials have always been a hot topic in materials science research. As asubstrate materials in luminescent material industry, metal molybdates have novelproperties and great potential applications in various fields such as photoluminescence,sensor, catalysis, optical fibres and microwave applications, et al. At present, thedevelopment of practical and low-cost methods for fabricating a large number ofmolybdates materials are still a great challenge for researchers. The main work of thispaper is to fabricate of several hierarchical architectures molybdates luminescentmaterials with a high yield and good uniformity via mild sonochemistry andhydrothermal synthesis process. The influence of reaction parameters on themorphology and luminescence properties is proposed. The conclusions can be dividedinto the following three aspects:The novel hierarchical3D architectures of CaMoO4:20%Eu3+phosphors weresuccessfully prepared via a facile and efficient sonochemistry process by controllingthe fundamental experimental parameters (the acidity of precursor solution) for thefirst time. On the basis of the experimental process, a possible formation mechanismof all sorts of superstructures (flower-like and elliptic cylinder, dumbbells,doughnut-shaped and peony-like microstructures) was proposed. It is commonlyaccepted that the photoluminescence properties of inorganic materials are stronglydependent on their sizes, morphologies, surface defects, and crystallinity. Theinfluence of surface defects on the luminescence was studied by comparing theemission intensity of different morphologies products. SrMoO4hierarchical architectures microspheres were successfully prepared by an efficient sonochemistryprocess. The SEM image reveals that an individual microsphere is composed of tensof similar nanosheets. When Ln3+(Eu3+, Sm3+, Tb3+, Dy3+) were incorporated into thehost of SrMoO4, the energy transfer from MoO42-to Ln3+. And the multicoloremissions occur through characteristic transitions of Ln3+can be observed.BaMoO4:Eu3+micronoctahedrons and micron-flowers were successfully prepared viaa sonochemical route by controlling the acidity of reaction precursors and theconcentrations of reactants for the first time. It was found that size modulation couldbe easily realized by changing the concentrations of reactants and the acidity ofreaction precursors. The formation mechanisms of ‘oriented aggregation-Ostwaldripening-self-assembly’ for micron-flowers and octahedrons was investigated in detail.The experimental results strongly suggest that small size of product has a veryimportant advantage on photoluminescence intensity due to large specific surfacearea.Large-scale and uniform CdMoO4:Ln3+(Ln=Pr, Sm, Eu, Dy, Ho and Er)microspheres phosphors were successfully obtained by a facile sonochemical method.We found that the Mo and Cd sources are critical to the formation of the microspheresstructures. The excitation and emission spectra of the Ln3+ions can be obtain underthe charge transfer band of the host, indicating that the energy transfer from host toLn3+ions is highly efficient. The quantum efficiency of the CdMoO4:Eu3+phosphor ismeasured by the integrated sphere method. The values is found to be about43.94%. Itis higher than that of the commercial red-emitting Y2O3:Eu3+(12.2%) and Y2O2S:Eu3+(35.0%), respectively. In addition, CdMoO4:Tb3+green phosphor was first fabricatedby a simple hydrothermal process. The morphology and size of the products can becontrolled by simply tuning the amounts of PEG and reaction time. The optimumconcentration of Tb3+ions was determined to be about5%in CdMoO4:Tb3+phosphors.And the result indicates that the process of energy transfer among the nearestneighbor ions is the main mechanism of concentration quenching of the Tb3+ions inCdMoO4host material.PbMoO4:Eu3+nanocrystals (NCs) with homogeneous grain size (37.08nm) were successfully synthesized via a facile sonochemistry process. The effects of Eu3+ionsdoping concentration on lattice constants and photoluminescence property waspresented. Based on the experimental results and the theoretical calculation, theoptimum Eu3+doping concentration and critical transfer distance (Rc) are5%and15.05, respectively.