Energy Transfer And Quantum Cutting Of Rare-earth-based Oxide Phosphors

Rare-earth-based quantum cutting phosphors have been extensively researched for their appliacation in PDPs, Mercury free lamps and Solar cells. In the present work, the phenomena of quantum cutting and energy transfer in oxysalts doped with different rare-earth ions have been investigated. The content of this paper includes three point:1. GdBO3:Tb3+ and KSr(Gd,Y)(PO4)2:Tb3+ phosphors were synthesize using the high temperature solid-state reaction method. The visible quantum cutting via cross relaxation between Tb3+ ions was observed via spectroscopic analysis. Upon excitation in the 4f75d1 states of Tb3+ in GdBO3:Tb3+and KSr(Gd,Y)(PO4)2:Tb3+, the quantum cutting occurred via a energy transfer process:the Tb3+ ion first relaxes from the 4f75d1state to an intermediate 5Dj state. During the relaxation, the released energy excites a neighboring Tb3+ to its 5D4 level by cross relaxation. Then, the original Tb+ and the neighboring Tb+ ions revert to their ground states by emitting two visible photons. The optimal quantum efficiency of GdBO3:Tb3+ and KSr(Y,Gd)(PO4)2:Tb3+ is 174% and 183%, respectively.2. A novel near-infrared (NIR) quantum cutting KCaGd(PO4)2:Ce3+,Yb3+ phosphor was successfully developed using the thermal decomposition of the corresponding nitrate. Due to the cooperative energy transfer from one Ce3+ to two Yb3+, an intense NIR emission around 1021 nm of Yb3+:2F5/2-2F7/2 transition was obtained under 324 and 280 nm excitation. Yb3+ concentration dependent quantum efficiency has been calculated and the theoretical maximum efficiency approaches up to 158.2%. Because the emission of Yb3+ around 1021 nm is matched with the band gap of crystalline Si, the phosphors could be a potential candidate for silicon-based solar cells.3. tm3+-Dy3+ co-activated Ba2Gd(BO3)2Cl and K3Gd(PO4)2 were synthesize using the high temperature solid-state reaction method. Upon direct excitation Tm3+ from its 6F6 level to 1D2 level, the decrease of emission intensity and lifetime of Tm3+1D2-3F4 emission with increasing concentration of Dy34 in Ba2Gd(BO3)2Cl: Dy3+, Tm3+ and K3Gd(PO4)2:Dy34, Tm3+ confirmed the occurrence of energy transfer from Tm34 to Dy34. Besides, Ba2Gd(BO3)2Cl:Dy3+, Tm3+ and K3Gd(PO4)2: Dy3+, Tm34 could be efficiently excited by 358 nm UV light and its emission color could be tuned from blue to yellow by codoping Tm34. For Ba2Gd(BO3)2Cl: 0.01Tm34, 0.05Dy34 and K3Gd(PO4)2:0.01Tm34,0.08Dy3+, intensive white emitting light with CIE of (0.352,0.328) and (0.338,0.347) was achieved upon 358 nm excitation.