Self-luminescent Tungstate/Molybdate Film Materials

The crystals of CaWO₄, PbWO₄, NaBi (WO₄) ₂ and CaMoO₄ with Scheelite structure (ABO₄) are better scintillators or X-ray emitters. The results show that the molybdate and tungstate with Scheelite structure belong to tetragonal system, and their grains are tetragonal, biconical or plate-like. They are important photoelectric functional materials, scintillating materials and fluorescent materials.

At present, single crystals or powders of molybdate and tungstate can be successfully synthesized by traditional Czochralski method, coprecipitation method and solid state reaction method, but it is difficult to obtain high quality molybdate or tungstate films. In practical applications, the display panel made of luminescent powder has better performance than the luminescent film, such as contrast, resolution, heat conduction, uniformity, adhesion to the substrate and gas release rate. The application of thin film materials in industry is more extensive. Therefore, it is undoubtedly of great significance to find a technology for preparing high quality tungstate and molybdate films.

Previous studies have shown that scheelite films without crystallization or inadequate crystallization do not have luminescent properties. Defects in the films also greatly affect the luminescent properties of scheelite structure films. In traditional preparation methods, such as radio frequency sputtering or chemical vapor deposition, a heat treatment process is often needed to crystallize the films. The volatility of WO₃ and MoO₃ results in defects in the prepared tungstate or molybdate films, which results in the degradation of the luminescent properties of tungstate and molybdate films. Therefore, the preparation of high quality tungstate and molybdate thin films at lower temperatures has become a key technology.

In order to overcome the shortcomings of tungstate and molybdate thin films prepared by traditional thin film preparation technology, researchers used the principle of galvanic cell to prepare crystalline scheelite structured luminescent films directly in aqueous solution without heating, thus achieving high quality tungstate and molybdate thin films at lower temperatures.

The process is to connect the metal substrate of scheelite luminescent film with platinum sheet by wire and put it into alkaline solution containing corresponding metal cations Ca, Ba, Sr, Pb, Cd or NaBi to form a primary battery system. The metal substrate is tungsten sheet or molybdenum sheet as cathode, platinum sheet as anode, and tungstate or molybdate film is grown on the cathode. The defects in the crystallization process of the films prepared by traditional methods are avoided without heating. The films show a single scheelite structure and crystalline state. The luminescent properties of CaMoO₄, SrMoO₄, CaWO₄ and SrWO₄ films are observed at room temperature.

• < Prev
• Next >