Collaborative Research: Multi-Photon Phosphors Based on Vacuum Collaborative Research: Multi-Photon Phosphors Based on Vacuum Ultraviolet Excitation Ultraviolet Excitation R. S. MeltzerR. S. Meltzer, University of Georgia , University of Georgia (DMR-0305400)(DMR-0305400)

Efforts are underway to develop a Efforts are underway to develop a new generation of mercury-free new generation of mercury-free fluorescent lamps with improved fluorescent lamps with improved efficiency. A near unity quantum efficiency. A near unity quantum yield has been demonstrated yield has been demonstrated using photon cascade emission using photon cascade emission (PCE) of Gd(PCE) of Gd3+3+ sensitized by VUV sensitized by VUV excitation of the self-trapped excitation of the self-trapped exciton (STE) in ScBOexciton (STE) in ScBO33. In PCE an . In PCE an ion decays in a sequential two-ion decays in a sequential two-step decay thereby emitting two step decay thereby emitting two photons for each photon absorbed photons for each photon absorbed (quantum splitting). The figure (quantum splitting). The figure shows the STE emission of pure shows the STE emission of pure ScPOScPO44(red curve) at 210 nm. In (red curve) at 210 nm. In Gd-doped ScPOGd-doped ScPO44 (blue curve) the (blue curve) the STE emission is almost absent in STE emission is almost absent in favor of emission from the favor of emission from the 66G and G and 66P states of GdP states of Gd3+3+. The . The 66G state G state emits sequentially a red (600 nm) emits sequentially a red (600 nm) and UV(313 nm) photon. The and UV(313 nm) photon. The total quantum yield is 1 photon total quantum yield is 1 photon out for each input photon. While out for each input photon. While this still lies below the desired this still lies below the desired value of at least 1.5 it value of at least 1.5 it demonstrates a new route to demonstrates a new route to efficiently populate the efficiently populate the 66G state of G state of GdGd3+3+ for quantum cutting for quantum cutting application either through PCE or, application either through PCE or, alternatively, a cross relaxation alternatively, a cross relaxation energy transfer scheme.energy transfer scheme.

200 300 400 500 600 700 800 9000

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Total Quantum Yield = 1

Collaborative Research: Multi-Photon Phosphors Based on Vacuum Collaborative Research: Multi-Photon Phosphors Based on Vacuum Ultraviolet Excitation Ultraviolet Excitation R. S. MeltzerR. S. Meltzer, University of Georgia , University of Georgia (DMR-0305400)(DMR-0305400)

Two Ph.D. students and two visiting Two Ph.D. students and two visiting scholars, Professor Hyo Jin Seo scholars, Professor Hyo Jin Seo (Pukyong National University, Korea) (Pukyong National University, Korea) and Dr. Sergey Feofilov, (Ioffe Institute and Dr. Sergey Feofilov, (Ioffe Institute in St. Petersburg, Russia), are in St. Petersburg, Russia), are currently involved with this project. currently involved with this project. This research provides an opportunity This research provides an opportunity for the students to gain expertise in for the students to gain expertise in phosphor development and to acquire phosphor development and to acquire the fundamental concepts in the the fundamental concepts in the optical properties of solids, especially optical properties of solids, especially those of rare earth doped insulators those of rare earth doped insulators which form the basis for many which form the basis for many phosphors. The training includes the phosphors. The training includes the gamut of techniques involved in gamut of techniques involved in vacuum ultraviolet (VUV) vacuum ultraviolet (VUV) spectroscopy. Close cooperation in this spectroscopy. Close cooperation in this project with scientists at Osram project with scientists at Osram Sylvania allow students to understand Sylvania allow students to understand the interfacing of research and the interfacing of research and development in an industrial setting. development in an industrial setting. Collaborating in this project is Collaborating in this project is Professor Keszler’s group at Oregon Professor Keszler’s group at Oregon State University; they design and State University; they design and produce the phosphors used in this produce the phosphors used in this effort. Students at the two Universities effort. Students at the two Universities see first hand the synergy necessary to see first hand the synergy necessary to develop new materials. develop new materials.

Mr. Zhou, a Ph.D. graduate Mr. Zhou, a Ph.D. graduate student, and student, and Dr. Feofilov, a visiting scientist, Dr. Feofilov, a visiting scientist, are shown operating the VUV are shown operating the VUV spectroscopy system.spectroscopy system.