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2 results

  • 8 - Pressure

  • from Part II - The Atomic Origins of Thermodynamics and Kinetics
  • Brent Fultz, California Institute of Technology
  • Book:
    Phase Transitions in Materials
    Published online:
    24 April 2020
    Print publication:
    14 May 2020, pp 204-222

  • Summary

    Phase transitions are driven by pressure as well as temperature, and the use of pressure to tune the electronic structures of materials can help further our understanding of materials properties. Chapter 8 begins with basic considerations of the thermodynamics of materials under pressure, and how phase diagrams are altered by temperature and pressure together. Volume changes can also be driven by temperature through thermal expansion, and the concept of “thermal pressure” from nonharmonic phonons is explained. Electronic energy is responsible for big contributions of +PV to the free energy, and this chapter describes how electron energies are altered by pressure. Cross-terms between temperature and pressure are discussed. The chapter ends with a discussion of kinetic processes under pressure, and the concept of an activation volume.

  • Synthesis, structure, and photoluminescence properties of Ce3+ and Tb3+ doped alkaline-earth silicate Sr2MgSi2O7 phosphors for WLEDs

  • Yongqian Wang, Yan Chen, Qimeng Sun, Bing Yan
  • Journal:
    Journal of Materials Research / Volume 32 / Issue 3 / 14 February 2017
    Published online by Cambridge University Press:
    12 January 2017, pp. 547-556
    Print publication:
    14 February 2017

  • In this research, Ce3+ and Tb3+ doped alkaline-earth silicate Sr2MgSi2O7 phosphors have been synthesized by solid-state reaction. The results show that the Sr2−x MgSi2O7:xCe3+ phosphors exhibit a violet–blue emission with excitation at 348 nm, whereas the Sr2−y MgSi2O7:yTb3+ phosphor show a green emission with excitation at 243 nm. In addition, the structure of Sr2MgSi2O7 host has been analyzed by Crystalmaker program. Staggered arrangements of [SiO4] and [MgO4] units in the Sr2MgSi2O7 system underlie possible chemical tuning and phase segregation, providing a potential candidate of tunable luminescence. A red shift of wave length is clarified by crystal field theory and Van Uitert expression. The FESEM image of Sr1.99MgSi2O7:0.01Ce3+ phosphors reveal that it has a proper particle size for application in WLEDs. With different Tb3+ doping concentration, the CIE chromaticity coordinates Sr2MgSi2O7:Tb3+ phosphors still remain a steady position. These results indicate that Sr2−x MgSi2O7:xCe3+, Sr2−y MgSi2O7:yTb3+ phosphors are promising phosphors for WLEDs.