Preparation and upconversion properties of Ba2ErF7 and Ba2ErF7:Yb3+ powders
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In this paper, defect-induced negative thermal quenching (NTQ) of Eu 2+ -doped phosphors is overviewed. NTQ denotes that the integrated emission intensity of a given phosphor increases continuously with increasing temperature up to a certain elevated temperature. The NTQ phenomenon of Eu 2+ luminescence was reportedly observed in a broad variety of lattices. The NTQ of these Eu 2+ -doped phosphors was generally ascribed to thermally stimulated detrapping of the excitation light stored in defects (traps) and subsequent energy transfer from the defects to the Eu 2+ 5d levels. Validity of defect- induced NTQ of Eu 2+ -doped phosphors is assessed and factors that may contribute to the measured emission intensity of a given phosphor at elevated temperatures are discussed. It is suggested that it is debatable whether NTQ could be an intrinsic property of the blue-emitting phosphor Na 3 Sc 2 (PO 4 ) 3 : Eu 2+ , and whether the emission intensity enhancement with increasing temperature for Eu 2+ -doped phosphors could be related to energy transfer from defects. The temperature dependence of the measured emission intensity alone seems not to be a good measure for evaluating TQ property of a phosphor, since it is affected by not only the quantum efficiency of the phosphor but also some extrinsic factors at elevated temperatures.
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In Gd3TaO7:0.01Bi 3+ , y Eu 3+ , the tuning of light from blue and green to red under UV excitation was achieved by adjusting the concentration of Eu 3+ , and a single-phase white phosphor suitable for a 365 nm LED chip was successfully synthesized.
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green phosphors have been prepared by the solution reaction method and the photoluminescence and crystalline properties were studied as a function of both the firing temperature (~) and the concentration of Mn activator (x=0.01~0.20). Under 147 nm and 254nm and excitation sources, the emission intensity of the phosphors was increased about 4 times increasing firing temperatures from to . From the XRD analysis, :Mn phosphors fired above showed willemite crystal structure. Under 147nm excitation, the maximum emission intensity was obtained at the Mn concentration of x=0.02 for phosphors fired at and the concentration quenching was occurred at the Mn concentration above x=0.10. The phosphor particles showed almost spherical shapes with the average size of around 2~3 by the SEM morphology.
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SrCaSiO4:Eu2+,Ce3+ has been prepared through high-temperature solid state reaction,and the spectrum and lifetime decay curves has been tested.The phosphors can match UV LED,and emit a broad band with a maximum at 500 nm.In SrCaSiO4:Ce3+,Eu2+ phosphors,energy transfer could been found between Ce3+ and Eu2+.In the fluorescent powder SrCaSiO4:Eu2+,the doping Ce3+ will make Eu2+ decay lifetime increase,and make Ce3+ decay lifetime become short,it also proves that there exist energy transfer.
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SrZnO2:Eu3+,M+(M=Li,Na,K) red-emitting phosphors were prepared by low-temperature combustion synthesis(LCS).The effect of the sensitizer Li+,Na+ and K+ on the emission spectra of ZnSrO2: Eu3+ phosphor was studied.It was presented that the emission spectrum intensity of SrZnO2:Eu3+ phosphor was enhanced by co-doped with alkali metal ions,and the relative luminescence intensity was the highest while n(Eu3+):n(Li+) was 1:3.The theoretical reason for the above results was analyzed.
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Red-emitting Ca3-xEuxZrSi2O9 (0.05 ≤ x ≤ 0.30) single phase phosphors were synthesized using the conventional solid-state reaction method and their photoluminescence properties were characterized. These phosphors exhibited typical emission peaks assigned to the transition from 5D0 to 7FJ (J = 0, 1, 2, 3, and 4) of Eu3+. The highest emission intensity was obtained for Ca2.83Eu0.17ZrSi2O9, where the relative emission intensity was 84% of that for a commercial red-emitting Y1.94Eu0.06O3 phosphor. The concentration quenching of the Eu3+-related luminescence in the Ca3-xEuxZrSi2O9 (0.05 ≤ x ≤ 0.30) phosphors can be mainly attributed to dipole-dipole interaction.
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