Abstract
Ultraviolet and visible upconversion emissions in Tb3+/Yb3+ co-doped YF3–BaF2–Ba(PO3)2 glasses were observed under 980-nm laser diode excitation. The dependence of the emission intensities of Tb3+ on the pump power reveals that two-photon processes account for blue cooperative emission of Yb3+ at 476 nm and green upconversion emission of Tb3+ at 543 nm, and three-photon processes for ultraviolet emission of Tb3+ in the wavelength range of 379–435 nm. The effects of Tb3+ concentration on the emission intensity and the lifetime of Tb3+ and Yb3+ are investigated in detail. It is found that the cooperative energy transfer from a pair of excited Yb3+ ions to a ground Tb3+ ion is responsible for the appearance of blue and green upconversion emissions due to the 5D4→7F J (J=6,5,4,3) transitions of Tb3+, and the resonance energy transfer from Yb3+ to Tb3+ accounts for the population on the 5D3,5G6 level and ultraviolet upconversion emission.
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