Molybdenum Tungstate Based Fluorescent Materials Preparation

In the early 1990s, GaN-based blue and purple light emitting diodes (LEDs) were first developed by Nichia Company in Japan, which made it possible for full-color LED display and semiconductor lighting. White LED has many advantages, such as all solid, cold light source, long life, small size, high light efficiency, good weather resistance and no mercury pollution. It has been widely used in lighting, display, automobile and other fields.

At present, a large number of researchers have carried out research on red fluorescent powder. Among them, the study of red fluorescent powder in molybdate and tungstate systems has become a hot spot. Due to the disordered layered structure and poor thermal conductivity of molybdate, tungstate with good physical and chemical properties can be used to improve the performance of molybdate, and the luminescence efficiency of fluorescent materials can be further improved by considering appropriate starter. The preparation method of molybdenum tungstate based fluorescent materials by high temperature solid state method includes the following steps:

(1)Raw materials of Na₂0MoO₄·2H₂O, WO₃, Y₂O₃, MoO₃, Na₂CO₃, and Eu₂O₃ are weighed according to the molar ratios indicated by the chemical formula of 0.1Eu³⁺:Na₅Y_0.9(WO₄)₂(MoO₄)₂.

(2)Above-mentioned raw materials are ground in corundum mortar for more than half an hour until they are mixed evenly. Then they are loaded into platinum crucible and heated in high-temperature heating furnace. A heating program is set up by a temperature controller. The heating temperature program is raised from room temperature to 600 ℃ at a rate of about 70 ℃/h, and the temperature is increased from room temperature to 600 ℃ At this temperature, sintering for 6 hours at constant temperature, then cooling at 60 C/h to 180 C, starting to stop the power supply of resistance furnace, and finally let the material cool naturally to room temperature and take out.

(2)Europium-doped sodium yttrium tetramolytungstate red fluorescent powder material can be obtained by grinding the sample in corundum grinding bowl again and sieving the sample in 200 mesh sieve. This is a typical molybdenum-tungstate-based fluorescent material.

The excitation spectra of fluorescent materials are in the range of 250-550 nm, and the two main absorption peaks are near 395 and 465 nm, which are in good agreement with the emission peaks of InGaN-based blue and purple LED wafers. Therefore, the fluorescent materials can be effectively excited by InGaN-based LED wafers.

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