Speaker: Thomas Tolhurst
Location: Physics 175
Time: 3:30 June 30 2015
Next-generation phosphors for solid-state lighting studied with X-ray spectroscopy and density functional theory
Abstract: The recently reported nitridolithoaluminate Sr[LiAl3N4]:Eu2+ and nitridomagnesosilicate Sr[Mg3SiN4]:Eu2+ are leading candidates for use in the next generation of phosphor-converted light-emitting diodes (pc-LEDs). They have garnered special interest due the their uniquely narrow bandwidths for Eu2+doped phosphors and high emission intensities in the critical, red region of the electromagnetic spectrum. A presentation of key features of their electronic structures, determined through density functional theory calculations and experimental soft X-ray spectroscopy measurements, will be given. This study builds on previously reported results observed through X-ray diffraction, visible light excitation and electron energy loss spectroscopy. Both materials are found to have large, indirect band gaps and an overall similar electronic structure. Both are narrow emitters, but Sr[Mg3SiN4]:Eu2+ shows the narrowest emissions to date of any red-emitting, Eu-doped phosphor. Further, they emit at noticeably different wavelengths in the red spectral region and have vastly different thermal quenching properties. These key differences in their emission properties in the visible region can be tied to subtle differences in their respective electronic structures. This talk will outline these structural differences and how they lead to the observed differences in the visible emissions of these phosphors.