Rodríguez-Vélez, Teddy A.

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    Spectroscopic studies of Mn/Eu doped phosphates, silicates and borates
    (2006) Rodríguez-Vélez, Teddy A.; Jia, Weiyi; College of Arts and Science - Science; Castellanos, Dorial; Marrero, Pablo; Department of Physics; Walker-Ramos,Uroyoán R.
    Lighting consumes about 23% of electric energy nationwide. Any improvement in lighting efficiency will lead to huge benefits for our society. The first generation of light sources was the incandescent lamp with an energy efficiency of only 5%, and has been replaced gradually by fluorescence lamps with an energy efficiency of more than 28%. Further improvement of fluorescent lamps now encounters a bottleneck. New lighting physics concepts have been explored within the last two decades. These include quantum cutting phosphor fluorescent lamps which have become very competitive due to their high energy efficiency, low cost, small volume and weight, and long lifetime. Currently, most commercial LEDs’ light sources are single color. For white LED sources, the most promising devices are phosphor-coated LEDs, in which LEDs emission is down- converted to white light. There are two kinds of designs: (a) blue LEDs plus yellow phosphors and (b) UV LEDs plus tricolor phosphors. The purpose of this project is to search for efficient phosphors which can be used as LED-phosphors white light sources. Three groups of materials were examined: (a) phosphates, M2P2O7 (M=Mg, Ca, Sr, Ba); (b) silicates, A2MSi2O7 (A= Sr or Ba, and M=Mg or Zn); and borates Ba2MgB2O6 and LiBa2BB5O10. These materials are single or double doped with Eu2+ and Mn2+. All phosphors were prepared with standard ceramic technology. X-ray diffraction, photoluminescence, temperature dependence of luminescence, and the excitation spectrum of phosphors were studied. Various results were found: first, that efficient energy transfer was observed from Eu2+ to Mn2+. This energy transfer allows the red emission of Mn2+ to be enhanced by sensitization with Eu2+. Secondly, in Mg2P2O7:Eu2+,Mn2+ and Sr2MgSi2O7:Eu2+,Mn2+, strong emission bands in blue and red were found under UV excitation. The phosphor then provides two basic colors. This could be an interesting application for LED-tricolor phosphor devices. Thirdly, a strong green emission was detected in Ba2ZnSi2O7 doped with Eu2+ or Eu2+/Mn2+ and Ba3ZnSi2O8 doped with Eu2+ or Eu2+/Mn2+. These phosphors can be used as the green component for LED-phosphor white light devices. Fourthly, Ba2MgB2O6:Eu2+ has strong a orange emission near 600nm that can be used to improve color rendering in LED-phosphors devices. Finally, LiBa2BB5O10:Eu2+ showed a blue- green emission, instead of a red emission previously reported in the literature. Although the blue-green emission may not be an ideal green component for the tricolor system, this strong UV emission provides a clue indicating that the host might be a good wide band gap semiconductor. In addition, the energy level assignments for Mn2+ and Eu2+, energy transfer between Eu and Mn, and the blue-shift of Eu emission bands are discussed. A modified single coordinate configuration for Eu2+ is proposed to explain the blue-shift of Eu2+ crystalline hosts.