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Zhang W.J.,Institute of Optical Communication Materials | Chen Q.J.,Institute of Optical Communication Materials | Qian Q.,Institute of Optical Communication Materials | Zhang Q.Y.,Institute of Optical Communication Materials | Jiang Z.H.,Institute of Optical Communication Materials
Physica B: Condensed Matter | Year: 2010

This paper reports on cooperative energy transfer and upconversion luminescence properties of Tb3+/Yb3+- and Nd3+/Yb3+/Tb3+-codoped oxyfluoride glasses. Upon excitation with a 980 nm laser diode, an intense green upconversion luminescence along with weak ultraviolet (UV)-visible emissions has been observed in Yb3+/Tb3+-codoped oxyfluoride glasses. Power dependence of UV-visible upconversion luminescence intensity has been examined, revealing that a cooperative energy transfer mechanism from Yb3+ ions is responsible for the excitation of Tb3+ ions. Meanwhile, it is noticed that Tb3+ upconversion emission bands have also been clearly detected at 487, 542, 587 and 620 nm in Nd3+/Yb3+/Tb3+-codoped oxyfluoride glasses upon excitation with a 808 nm laser diode. The quadratic dependence of the upconversion luminescence on the pump-laser power indicates two-photon process for the population of Tb3+:5D4 state via Nd3+→Yb3+→Tb3+ energy transfer. However, no emission has been observed in the oxyfluoride glasses codoped with Yb3+/Tb3+ or Nd3+/Tb3+, respectively, upon excited at a 808 nm laser diode. A proposed upconversion mechanism involving energy transfer from Nd3+ to Yb3+, and then a cooperative energy transfer process from two excited Yb3+ to Tb3+ has been presented. © 2009 Elsevier B.V. All rights reserved.

Zhang Q.Y.,Institute of Optical Communication Materials | Huang X.Y.,Institute of Optical Communication Materials
Progress in Materials Science | Year: 2010

Luminescent materials with the quantum efficiency (QE) higher than unity could be playing a significant role in the progress of lighting industry and certain electronic display systems. The recent demonstration of an efficient visible quantum cutting (QC) in vacuum ultraviolet (VUV)-excited LiGdF4:Eu phosphors [Wegh RT, Donker H, Oskam KD, Meijerink A. Visible quantum cutting in LiGdF4:Eu3+ through downconversion. Science 1999; 283: 663-6] has provided an exciting and interesting trends in the development of several potentially important luminescent materials and devices. The possibility of the higher QE depends on the principle of QC in phosphors which could generate two or more low-energy photons for every incident high-energy photon that is being absorbed by phosphors. Investigation on QC systems has started on single ions doped-fluorides capable of a cascade emission from ions such as Pr3+, Tm3+, Er3+ and Gd3+. The focus has now been shifted to the combination of two ions, where the energy of the donor ion could be transferred stepwise to two acceptor ions via a downconversion. A well-known example is the Gd3+-Eu3+ dual ions. QC via downconversion has now been widely witnessed in many rare earths (RE)-based phosphors, the interesting and appreciable QE in the visible spectral region has earlier been reported from LiGdF4:Eu (190%) and BaF2:Gd,Eu (194%) phosphors. QC materials could also be used in solar cells, if conversion of one UV-visible photon into two near-infrared (NIR) photons is realized, and energy loss due to thermalization of electron-hole pairs is minimized. The present article reviews on the recent progress made on: (a) materials and developments in the fields of UV-visible QC phosphors and the mechanism involved, including QC in single RE ion activated fluorides- and oxides-based phosphors, energy transfer and downconversion, QC in dual/ternary ions activated phosphors; and (b) NIR QC in RE3+-Yb3+ (RE = Tb, Tm, and Pr) dual ions doped phosphors via cooperative energy transfer. Appropriate discussions have been made on materials, materials synthesis and characterization, the structural and luminescence properties of various QC luminescent materials via different synthesis techniques. In addition, applications, challenge and future advances of the visible- and NIR-QC phosphors have also been dealt with. © 2009 Elsevier Ltd. All rights reserved.

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