Jun-Lin Yuan

Energy transfer mechanisms in Tb3+, Yb3+ codoped Y2O3 downconversion phosphor

Tb3+ and Yb3+ co-activated luminescent material that can cut one photon of around 483 nm into two NIR photons of around 1000 nm could be used as a downconversion luminescent convertor in front of crystalline silicon solar cell panels to reduce thermalization loss of the solar cell. The Tb3+ → Yb3+ energy transfer mechanisms in the UV–blue region in Y2O3 phosphor were studied by PL excitation spectra and time-resolved luminescence, from which the charge transfer mechanism and the cooperative transfer mechanism were identified. Tb3+ ions in the 4f75d1 state relax down to the 5D4 level and cooperatively transfer energy to two Yb3+ ions, which is followed by the emission of two photons (λ ~ 1000 nm). It was found in the (Y0.79Tb0.01Yb0.20)2O3 sample that 37% of the Tb3+ ions at the 5D4 level transfer energy to two neighbouring Yb3+ ions by the cooperative energy transfer mechanism Tb3+ (5D4) → 2Yb3+ (2F5/2). Unfortunately, the high Yb3+ concentration leads to severe concentration quenching that significantly reduces the external quantum efficiency. Moreover, the energy of the Tb3+ 4f75d1 state can also be lost non-radiatively or transferred to the Yb3+ 2F5/2 state via the charge transfer state Tb4+–Yb2+. In conclusion, RE3+ (RE = Ce, Pr, Tb) with strong absorption in the UV region is not an appropriate sensitizer of Tb3+ in Tb3+–Yb3+ codoped downconversion phosphor.

Luminescence properties of CaZr(PO4)2:RE (RE = Eu3+, Tb3+, Tm3+) under x-ray and VUV–UV excitation

Novel phosphors of Eu3+, Tb3+ and Tm3+ doped CaZr(PO4)2 were synthesized by solid-state reactions and their x-ray and vacuum ultraviolet–ultraviolet (VUV–UV) spectroscopic properties were investigated. The bands near 147 or 185 nm in the VUV excitation spectra of those doped samples are attributed to the PO4 absorption and O to Zr charge transfer transition in the host. The excitation and emission spectra indicate that the phosphors can be effectively excited by x-ray or 147 nm and 172 nm and exhibit a satisfactory red, green and blue light performance, respectively. Considering the high luminescent intensity, excellent colour purity and chemical stability, CaZr(PO4)2:RE (RE = Eu3+ Tb3+, Tm3+) are attractive red, green and blue emitting x-ray and plasma display panel phosphors.

Luminescent properties of REBa3B9O18 (RE = Lu, Tb, Gd, Eu) under VUV excitation

The VUV excited luminescent properties of REBa3B9O18 (RE = Lu, Tb, Gd, Eu) were investigated. The bands near 160 nm in the VUV excitation spectra of those compounds are attributed to the host absorptions; at the same time, the energy of host absorption is shifted to a higher energy region with decreasing RE3+ radius. It is observed that there is energy transfer between the hosts and luminescent centres (e.g. Tb3+, Gd3+ and Eu3+). From the standpoints of colour purity and luminescent efficiency, the phosphor of TbBa3B9O18 is an attractive candidate for new green-emitting phosphors for plasma display panels and mercury-free fluorescent lamps.