A series of K3Gd1 x y(PO4)2:xCe3+,yTb3+phosphors are synthesized by the solid-sate reaction method.X-ray diffraction and photoluminescence spectra are utilized to characterize the structures and luminescence properties of the as-synthesized phosphors.Co-doping of Ce3+enhances the emission intensity of Tb3+greatly through an efficient energy transfer process from Ce3+to Tb3+.The energy transfer is confirmed by photoluminescence spectra and decay time curves analysis.The efficiency and mechanism of energy transfer are investigated carefully.Moreover,due to the nonconcentration quenching property of K3Tb(PO4)2,the photoluminescence spectra of K3Tb1 x(PO4)2:xCe3+are studied and the results show that when x=0.11 the strongest Tb3+green emission can be realized.
A complete solid solutions with monophasic zircon-type structure of vanadates of formula GdxBi0.95-xVO4:0.05Eu3+(x = 0–0.95) are synthesized by combined method of co-precipitation and hydrothermal synthesis. Their microstructures and morphologies are characterized by X-ray powder diffraction and transmission electronic microscope, and the results show that each of all the samples has a monophasic zircon-type structure. The absorption spectrum of the prepared phosphor shows a blue-shift of the fundamental absorption band edge with increasing the gadolinium content. Under UV-light and visible-light excitation, all the prepared phosphors show the typical luminescence properties of Eu3+in the zircon-type structure. The emission intensity of GdxBi0.95-xVO4:0.05Eu3+(x = 0.55) is strongest in all samples under UV-light and visible-light excitations. Finally, the mechanisms of luminescence of Eu3+in the GdxBi0.95-xVO4:0.05Eu3+(x = 0–0.95)solid solutions are analyzed and discussed.
Eu3+-activated red-emitting Ba2Gd2Si4O13 phosphors are prepared via microwave(MW) synthesis and solid-state(SS) method. The structural and luminescent properties of phosphors are investigated by X-ray diffraction(XRD), photoluminescence(PL) spectra and scanning electron microscopy(SEM). Upon 393 nm excitation, compared with the sample sintered by SS method, luminescence enhancement is observed in the sample synthesized by MW method. The mechanism of MW synthesis process is discussed in detail. Results indicate that the PL enhancement is probably related to the concave-convex phosphor surfaces and uniform grains, which may reinforce scattering of excitation light. Our research may further promote the understanding of MW synthesis and extend the application of Eu3+-activated Ba2Gd2Si4O13 in white light-emitting diodes.
K3Gd(PO4)2:Tb3+ phosphors are synthesized by the solid reaction method,and the phases and luminescence properties of the obtained phosphors are well characterized.The emission spectra of K3Gd(PO4)2:Tb3+ exhibit the typical emissions of Tb3+.Concentration quenching of Tb3+ is not observed in K3Gd(PO4)2:Tb3+,likely because the shortest average distance of Tb3+–Tb3+ in K3Gd(PO4)2:Tb3+ is adequately long such that energy transfer between Tb3+–Tb3+ ions cannot take place effectively.This result indicates that K3Tb(PO4)2 phosphors have potential application in near ultraviolet(n-UV)-convertible phosphors for white light-emitting diodes.
The green long-after-glow luminescence from Tb3+-doped Sr2SiO4phosphors, which are synthesized by the high temperature solid state reaction in a reductive atmosphere, is observed in this paper. The results show that under ultraviolet excitation, the obtained phosphors produce an intense green-lighting-emission from the Tb3+, and the green-lighting longafter-glow luminescence related to Tb3+can last half an hour after the irradiation source has been removed. Moreover,the effects of co-doping Li+, Dy3+, Er3+, Gd3+, and Yb3+with Tb3+on the decay properties and thermoluminescence properties are investigated to confirm the long-after-glow mechanism.
A series of K3Gd(PO4)2:Tb3+,Sm3+ phosphors were synthesized through solid state reaction. By co-doping Tb3+ and Sm3+into K3Gd(PO4)2 host and singly varying the doping concentration of Sm3+, tunable colors from green to yellow and then to orange were obtained in K3Gd(PO4)2:Tb3+,Sm3+ phosphors under the excitation at 373 nm. The energy transfer process from Tb3+ to Sm3+ was verified through luminescence spectra and fluorescence decay curves. Moreover, the energy transfer mechanism was demonstrated to be the quadrupole-quadrupole interaction. The results indicated that K3Gd(PO4)2:Tb3+,Sm3+ phosphors could be a potential application for n-UV white light emitting diodes.
A novel red-emitting phosphor, CaYAl3O7 : Eu 3+ , Sm3+ , is synthesized by a combustion method at a low temperature (850℃), and the single phase of CaYAl3O7 is confirmed by powder X-ray diffraction measurements. The photoluminescence property results reveal that the red emission intensity of Eu3+ is strongly dependent on the Sm3+ concentration. Only the Eu 3+ luminescence is detected in the Eu 3+ -Sm3+ co-doped CaYAl3O7 phosphor with 393 nm excitation. However, under the characteristic excitation (402 nm) of Sm3+ , not only the Sm3+ emission but also the Eu 3+ emission are observed. A possible mechanism of the energy transfer between Sm3+ and Eu 3+ is investigated in detail.
The upconversion(UC) of the rare earth doped glass-ceramics has been extensively investigated due to their potential applications in many fields, such as color display, high density memories, optical data storage, sensor and energy solar cell, etc. Many series of them, especially the oxyfluorides glasses containing Ba2 LaF 7 nanocrystals were studied in this review work, due to the thermal and mechanical toughness, high optical transmittance from the ultraviolet to the infrared regions, and a low nonlinear refractive index compared to the other commercial laser glasses. Moreover, the energy transfer(ET) between the rare earth ions and transition metals plays an important role in the upconversion process. The cooperative ET has been researched very activly in UC glasses due to applications in the fields of solar cells, such as in the Er/Yb, Tm/Yb, Tb/Yb, Tb/Er/Yb and Tm/Er/Yb couples. The present article reviews on the recent progress made on:(i) upconversion materials with fluoride microcrystals in glasses and the mechanisms involved, including the UC in double and tri-dopant RE ions activated fluoride microcrystal, energy transfer process; and(ii) the effect of the metal Mn and nanoparticles of Au, Ag, Cu on the enhancement of UC emissions. Discussions have also been made on materials, material synthesis, the structural and emission properties of glass-ceramics. Additionally, the conversion efficiency is still a challenge for the spectra conversion materials and application; challenge and future advances have also been demonstrated.
A novel white-emitting Ca_2Ga_2GeO_7:Dy^(3+) phosphor was synthesized via a high-temperature solid-state reaction.The crystal phase was analyzed by X-ray diffraction(XRD),and the photoluminescence(PL) properties were studied by luminescence spectra and fluorescence decay curves.Under the excitation of 347 nm,the obtained phosphor exhibited strong emission in the blue region peaked at 478 nm,yellow at 574 nm and a weak red emission band at 665 nm,corresponding to the characteristic transitions of ~4F_(9/2)to ~6H_(15/2),~6H_(13/2) and ~6H_(11/2) of Dy^(3+),respectively.By varying the doping concentration of Dy^(3+),tunable colors from blue-white to yellow-white were obtained in the phosphors.Besides,by codoping charge compensators(Li^+,Na^+,K^+ and Ga^(3+)) in Ca_2Ga_2GeO_7:Dy^(3+),the optimum CE color coordinate and PL intensity were obtained in Ca_2Ga_2GeO_7:Dy^(3+),K^+.Accordingly,the PL mechanism of Ca_2Ga_2GeO_7:Dy^(3+) was discussed briefly.
We synthesize continuous solid solutions with monophasic zircon-type structure of vanadates of formula YxBi0.95-xVO4:0.05Dy3+(x = 0–0.95) using a combined method of co-precipitation and hydrothermal synthesis. The X-ray diffractometer patterns confirm the formation of a solid solution of YxBi0.95-xVO4:0.05Dy3+, and the results show that all the samples have monophasic zircon-type structure. The absorption spectra of the prepared phosphors show a blue-shift of the fundamental absorption band edge with increasing Y3+ content. An intense tunable characteristic emission of Dy3+ is observed with the increasing ratio of Y/Bi. Finally, the mechanism of luminescence of Dy3+ in the Y3xBi0.95-xVO4:0.05Dy+(x = 0–0.95) solid solution is analyzed and discussed.
