Quantum cutting downconversion by cooperative energy transfer from Bi^(3+) to Yb^(3+) in Y_2O_3 phosphor

Bi3＋ and Yb3＋ codoped cubic Y2O3 phosphors are prepared by pechini sol-gel method. Strong near-infrared （NIR） emission around 980 nm from Yb3＋ （2F5/2＋2 F7/2） is observed under ultraviolet light excitation. A broad excitation band ranging from 320 to 360 nm, owing to the 6s2→6s6p transition of Bi3＋ ions, is recorded when the Yb3＋ emission is monitored, which suggests a very efficient energy transfer from Bi3＋ ions to Yb3＋ ions. The Yb3＋ concentration dependences of both the Bi3＋ and the Yb3＋ emissions are investigated. The decay curve of Bi3＋ emission under the excitation of 355 nm pulse laser is used to explore the Bi3＋ →＋Yb3＋ energy transfer process. Cooperative energy transfer （CET） is discussed as a possible mechanism for the near-infrared emission.

Cooperative energy transfer in Eu^(3+),Yb^(3+) codoped Y_2O_3 phosphor

Under 980 nm laser excitation,red emission(5D0-7FJ(J=0,1,2)) of Eu3+ was observed in cubic Y2O3 codoped with Eu3+ and Yb3+.The dependence of the upconverted emission on doping concentration and laser power was studied.Yb3+ emission around 1000 nm(2F5/2-2F7/2) was reported upon excitation of Eu3+ ions.The decay curves of 5DJ(J=0,2) emission of Eu3+ under excitation of 266 nm pulse laser were examined to investigate the Eu3+→Yb3+ energy transfer process.Cooperative energy transfer process was discussed as the...

Energy transfer in Tb^(3+),Yb^(3+) codoped Lu_2O_3 near-infrared downconversion nanophosphors

Tb3＋ and Yb3＋ codoped Lu2O3 nanophosphors were synthesized by the reverse-strike co-precipitation method. The obtained Lu2O3：Tb3＋,Yb3＋ nanophosphors were characterized by X-ray diffraction （XRD） and photoluminescence （PL） spectra. The XRD results showed that all the prepared nanophosphors could be readily indexed to pure cubic phase of Lu2O3 and indicated good crystallinity. The Tb3＋→Yb3＋ energy transfer mechanisms in the UV-blue region in Lu2O3 nanophosphors were investigated. The experimental results showed that the strong visible emission around 543 nm from Tb3＋ （5D4→7F5） and near-infrared （NIR） emission around 973 nm from Yb3＋ （2F5/2→2F7/2） of Lu2O3：Tb3＋,Yb3＋ nanophosphors were observed under ultraviolet light excitation, respectively. Tb3＋ could be effectively excited up to its 4f75d1 state and relaxed down to the 5D4 level, from which the energy was transferred cooperatively to two neighboring Yb3＋. The Yb3＋ concentration dependent luminescent properties and lifetimes of both the visible and NIR emissions were also studied. The lifetime of the visible emission decreased with the increase of Yb3＋ concentration, verifying the efficient energy transfer from the Tb3＋ to the Yb3＋. Cooperative energy transfer （CET） from Tb3＋ to Yb3＋ was discussed as a possible mechanism for the near-infrared emission. When doped concentrations were 1 mol.% Tb3＋ and 2 mol.% Yb3＋, the intensity of NIR emission was the strongest.

Near-infrared downconversion in Eu^(2+) and Pr^(3+) co-doped KSrPO_4 phosphor

A novel near-infrared （NIR） downconversion （DC） phosphor KSrPO4：Eu2＋, Pr3＋ is synthesized by the conventional high temperature solid-state reaction. The Eu2＋ acts as an efficient sensitizer for Pr3＋ in the KSrPO4 host. With broad- band near-ultraviolet light excitation induced by the 4f→5d transition of Eu2＋, the characteristic NIR emission of Pr3＋, peaking at 974 nm and 1019 nm due to 3po →1G4 and 1G4→3H4 transitions, is generated as a result of the energy transfer from Eu2＋ to Pr3＋. The luminescence spectra in both the visible and the NIR regions and the decay lifetime curves of Eu2＋ prove the energy transfer from Eu2＋ to Pr3＋. This Eu2＋ and Pr3＋ co-doped KSrPO4 phosphor may be a promising candidate to modify the spectral mismatch behavior of crystalline solar cells and sunlight.

Efficient near-infrared quantum cutting in Tb3＋,Yb3＋ codoped LuPO_4 phosphors

Tb^（3＋） and Yb^（3＋） codoped LuPO_4 phosphors were prepared by the reverse-strike co-precipitation method.The obtained LuPO_4：Tb^（3＋）,Yb^（3＋） phosphors were characterized by X-ray diffraction（XRD）,photoluminescence（PL） spectra and decay kinetics to understand the near-infrared quantum cutting（QC） phenomena.The XRD results showed that all the phosphors exhibited good crystallinity and had a pure tetragonal phase of LuPO_4.The experimental results showed that the strong green emission around 545 nm from Tb^（3＋）（~5D_4→~7F_5） and near-infrared（NIR） emission at 1003 nm from Yb^（3＋）（~2F_（5/2）→~2F_（7/2）） of LuPO_4：Tb^（3＋）,Yb^（3＋）phosphors were observed under 489 nm excitation,respectively.The Yb^（3＋） concentration dependence on luminescent properties and lifetimes of both the visible and NIR emissions were also investigated.The quenching concentration of Yb^（3＋） ions approached as high as 10 mol.%.The excellent luminescence properties of the LuPO_4：Tb^（3＋）,Yb^（3＋） indicated its potential application in improving the energy conversion efficiency of the silicon based solar cells by converting one blue photon to two NIR ones.

Efficient near-infrared quantum cutting by Ce^(3+)-Yb^(3+) couple in GdBO_3 phosphors

Ce3＋ and Yb3＋ co-activated GdBO3 phosphors were prepared by a conventional solid-state reaction method. X-ray powder diffraction, photoluminescent spectra and decay curves were used to characterize their structural and luminescent properties. An efficient near-infrared （NIR） quantum cutting （QC） from the phosphors was observed, which involved the emission of two low-energy NIR photons （around 971 nm） from an absorbed ultra-violet （UV） photon at 358 nm via a cooperative energy transfer （CET） from Ce3＋ to Yb3＋ ions. The theoretical quantum efficiency was calculated and the maximum efficiency approached up to 164% before reaching the critical concentration quenching threshold. Our results demonstrated that these phosphors might find potential application in improving the efficiency of silicon based solar cells.