Coherent emission at 1.047 μ from trivalent praseodymium in calcium tungstate was observed. This emission coincides with strong infrared fluorescence at the same wavelength and was found to be stimulated mostly by absorption of blue light by the ³P₀, ³P₁, and ³P₂ bands. The emission corresponds to a ¹G₄↠³H₄ transition with the terminal level 377 cm−1 from the ground state. The oscillation threshold was the same at 4.2°, 20°, and 78°K. No stimulated emission was observed at room temperature. The lifetime of the metastable state ¹G₄ is 50×10−3 sec. A new technique used to measure the lifetime is described. 

 

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Tungsten diselenide (WSe2) conductivity is ten parts per million than the best conductivity which is diamond, it is the world's lowest conductivity material. In general, poor conductivity material (or insulator) is a porous material, but also one of the most insulation materials. Tungsten diselenide has low thermal conductivity, which is the system heat loss is not easy, so the system's energy conversion efficiency will be higher. If can full to use its insulation properties, will likely significantly increase the efficiency of energy use.
And because the main structure is composed of the upper and lower layer which is the selenium atom and the intermediate layer are tungsten atoms. This structure of WSe2 material like graphene can absorb light and the light absorption can be used to produce electricity. With further study, the researchers according to this feature of tungsten diselenide developed diodes which produce by tungsten diselenide, and this material can be applied to thin flexible solar cells.

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Average grain size and distribution of particle of ammonium paratungstate is affected by the PH value of solution. Nucleary speed and crystalline speed is affected by PH value apparently. After crystallization, the PH value is controlled between 8.0-7.8, it will reduce the nucleary amount and forming speed, the small amount of crystal nucleus can turn into large grain size steadily, also the limited PH value will make the coarse ammonium paratungstate which is distributed evenly.

Adding 10%-20% dilute hydrochloride acid into solution to the PH value 6.5-7.5, the apparent density of crystal decreases, the crystal shape is regular which makes it more convenient to prepare fine ammonium paratungstate particle. By adjusting crystallization mother liquor to the ideal PH value 6.0-8.0 and heat to above 50 degree Celsius will obtain high purity ammonium paratungstate crystal.




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Tungsten diselenide is a gray inorganic compound, the main structure is composed of the upper and lower layer which is the selenium atom and the intermediate layer is tungsten atoms. Besides, every layer combined with van der Waals force, so tungsten diselenide in sixth metal dichalcogenides are very stable semiconductors. Its physical properties are as follows: the chemical formula: WSe2, molar mass: 341.76 • mol-1, density 9.32, CAS number: 12067-46-8.
Tungsten diselenide is often used in solar cells photovoltaic devices, while WSe2 photoelectrode in very stable under acidic and alkaline, and therefore it can be used in photovoltaic chemical barrier. Also WSe2 monolayer which is mechanical exfoliation can be used in the production of transparent photovoltaic equipment and ultra-thin LED.
Producing tungsten diselenide can put tungsten sheet in selenium vapor at high pressure and high temperature (over 800K) heating, then using sputtering deposition techniques to form hexagonal crystal on the sheet with right element proportion.

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