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Phosphors - Phosphor Materials

Phosphor, commonly known as luminous powder, is usually divided into light-induced energy-storing luminous powder and radioactive luminous powder. Light-induced energy-storing luminous powder refers to phosphor that stores the light energy after being irradiated by natural light, sunlight, ultraviolet light and so on, and then slowly releases the light energy in the form of fluorescence after stopping the light irradiation. Therefore, the phosphor can still be seen glowing at night or in the dark, and can last for several hours to more than ten hours. Phosphors usually contain various types of transition metals or rare earth compounds. Phosphorescent materials are commonly used in CRT and plasma displays, fluorescent lamps, sensors and white LEDs.

 The luminous principle of white LEDFigure 1. The luminous principle of white LED

Applications:

  • Phosphor for ordinary fluorescent lamps and low-pressure mercury lamps: Fluorescent powders used in fluorescent lamps and low-pressure mercury lamps include antimony, manganese activated calcium halophosphate phosphors and rare earth tricolor phosphors. Antimony and manganese activated calcium halophosphate phosphors are prepared by adding a small amount of antimony (Sb) and manganese (Mn) into fluorochlorapatite matrix 3Ca3(PO4)2Ca(F,Cl)2 as activators. When the activator Sb absorbs the excitation energy and releases part of the energy in the form of light radiation, calcium halophosphate phosphors with different color temperatures can be obtained by changing the content of Mn. Among the rare earth tricolor phosphors, the red powder is europium activated yttrium oxide (Y2O3: Eu), the green powder is cerium and terbium activated aluminate (MgAl11O19: Ce, Tb), and the blue powder is low-valent europium activated barium magnesium aluminate (BaMg2Al16O27: Eu).
  • Phosphors of different colorsFigure 2. Phosphors of different colors

  • Phosphor for high-pressure mercury lamps: The spectral distribution of high-pressure mercury lamp is significantly different from that of low-pressure mercury lamp (fluorescent lamp). In order to improve the efficiency and color of the lamp, the glass shell outside the discharge tube of the high-pressure mercury lamp is coated with phosphor to convert the energy of ultraviolet radiation with a wavelength of 365nm into visible light. In the early stages, manganese-activated magnesium fluorogermanate or tin-activated zinc strontium phosphate powder was used in high-pressure mercury lamp. Later, Y(PV)O4: Eu phosphor has been developed, which is more suitable for high-pressure mercury lamp. The phosphor YVO4: Eu, used for color TV has a peak value of 619nm, and the lamp using YVO4:Eu has high total luminous flux and good color rendering performance.
  • Phosphor for ultraviolet light source: This phosphor can produce another kind of ultraviolet with longer wavelength under the excitation of ultraviolet with a wavelength of 253.7nm or other shorter wavelengths. There are many types of phosphors used as ultraviolet light sources. (BaSi2O3:Pb) phosphor is an effective ultraviolet phosphor with a peak value of 350nm, which is used as a black light to trap and kill insect pests. Calcium orthophosphate ((Ca,Zn)3(PO4)2:Ti) phosphor is a kind of high-efficiency powder for lamp with emission wavelength of 280nm and 350nm and the peak value is 310nm. The photocopy lamp must have spectral lines that match the absorptivity of the photosensor or photoelectric surface used, so strontium pyrophosphate (Sr2P2O7: Eu), magnesium gallium gallate (MgGa2O4: Mn), zinc silicate (Zn2SiO4: Mn) and other ultraviolet phosphors are used in diazo photocopying lamps.

References:

  1. MEI Y, JIA Y C, YOU H P, et al. (2010) "Synthesis and luminescent properties of NaLa(MoO4)Z: Eu3+ shuttle-fike nanorods composed of via nanoparticles." CrystEngComm, 13:4046-4052.
  2. HAQUE M M, LEE H I, KIM D K (2009). "Luminescent properties of Eu3+-activated molybdate-based novel red-emitting phosphors for LEDs".J. Alloys Comp.481:792-796.

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