Spectral Modification and Quantum Cutting in RE3+-Yb3+ (R=Pr, Tm, and Tb) Codoped Transparent Glass-ceramics Containing CaF2 Nanocrystals

We report on the cooperative energy transfer process in RE3+-Yb3+ (RE=Pr, Tm and Tb) codoped transparent glass-ceramics containing CaF2 nanocrystals, which are capable of splitting a visible photon absorbed by RE3+ into two near infrared photons emitted by Yb3+. The formation of CaF2 nanocrystals in the glass-ceramics was confirmed by X-ray diffraction measurement. Yb3+ emission in the wavelength range of 950- 1100 nm (F-2(5/2) -> F-2(7/2)) was observed upon the excitation of P-3(0) energy level of Pr3+ at 482 nm, (1)G(4) energy level of Tm3+ at 468 nm, and D-5(4) energy level of Tb3+ at 484 nm, respectively, in the RE3+-Yb3+ co-doped glass-ceramics. The energy transfer process was proved by the excitation and emission spectra. The Yb3+ concentration dependent quantum efficiency was also evaluated individually in the codoped systems, which indicated that Pr3+-Yb3+ is the most efficient cooperative energy transfer couple. It was supposed that besides the cooperative energy transfer process, the (1)G(4) state, which may be populated by P-3(0)->(1)G(4) transition as a result of energy transfer to one Yb3+ ion from Pr3+ P-3(0) energy level, can also act as a donor state in the energy transfer to another Yb3+ ion. These rare-earth ions codoped transparent glassy materials may have potential applications for the enhancement of photovoltaic conversion efficiency of silicon solar cells via spectra modification.