Comparative analysis of energy-level splitting of Pr3＋ doped in LiYF4 and LiBiF4 crystals： a complete energy matrix calculation

Based on the combination of Racah's group-theoretical consideration with Slater's wavefunction, a 91 × 91 complete energy matrix is established in tetragonal ligand field D_2d for Pr³⁺ ion. Thus, the Stark energy-levels of Pr³⁺ ions doped separately in LiYF₄ and LiBiF₄ crystals are calculated, and our calculations imply that the complete energy matrix method can be used as an effective tool to calculate the energy-levels of the systems doped by rare earth ions. Besides, the influence of Pr³⁺ on energy-level splitting is investigated, and the similarities and the differences between the two doped crystals are demonstrated in detail by comparing their several pairs of curves and crystal field strength quantities. We see that the energy splitting patterns are similar and the crystal field interaction of LiYF₄:Pr³⁺ is stronger than that of LiBiF₄:Pr³⁺.     

A novel strong green phosphor： K3Gd（PO4）2：Ce^3＋, Tb^3＋ for a UV-excited white light-emitting-diode

A series of K3Gd1-x-y（PO4）2：xCe^3＋, yTb^3＋ 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 Ce^3＋ enhances the emission intensity of Tb^3＋ greatly through an efficient energy transfer process from Ce^3＋ to Tb^3＋. 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 non- concentration quenching property of K3Tb（PO4）2, the photoluminescence spectra of K3Tb1-x（PO4）2：xCe^3＋ are studied and the results show that when x = 0.11 the strongest Tb^3＋ green emission can be realized.     

A strong green-emitting phosphor： K3Gd（PO4）2：Tb3＋ for UV-excited 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.     

Novel Dy^3＋-doped Gd（PO3）3 white-light phosphors under VUV excitation for Hg-free lamps application

Novel Dy3+-doped Gd(PO3)3 white light phosphors each with an orthorhombic system are successfully synthesized by solid-state reaction.The luminescence properties of white-light Gd1-x(PO3)3:xDy3+(0 x ≤ 0.25) under vacuum ultraviolet(VUV) excitation are investigated.The strong absorption at around 147 nm in excitation spectrum energy can be transferred to the energy levels of Dy3+ ion from the host absorption.Additionally,the white light phosphor is activated by a single Dy3+ ion.Therefore,the luminescence of Gd1-x(PO3)3:xDy(0 x ≤ 0.25) under VUV excitation is effective,and it has the promise of being applied to mercury-free lamps.     

Optimum fluorescence emission around 1.8 μm for LiYF4 single crystals of various Tm3＋-doping concentrations

In this paper, optical spectra of LiYF4 single crystals doped with Tm3＋ ions of various concentrations are reported. The emission intensity at 1.8 ktm first increases with increasing Tm3＋ concentration, and reaches a maximum value when the concentration of Tm3＋ is about 1.28 mol%, then it decreases rapidly as the concentration of Tm3＋ further increases to 3.49 mol%. The emission lifetime at 1.8 p.m also shows a similar tendency to the emission intensity. The maximum lifetime of 1.8 μm is measured to be 17.68 ms for the sample doped with Tm3＋ of 1.28 mol%. The emission cross section of 3F4 level is calculated. The maximum reaches 3.76 × 10 -21 cm2 at 1909 nm. The cross relaxation （3H6, 3H4 →3 F4, 3F4） between Tm3＋ ions and the concentration quenching effect are mainly attributed to the change of emission with Tm3＋ concentration. The largest quantum efficiency between Tm3＋ ions is estimated to be ,-147% from the measured lifetime and calculated radiative lifetime. All the results suggest that the Tm3＋/LiYF4 single crystal may have potential applications in 2 μm mid-infrared lasers.     

Photoluminescence properties of Ce3＋ and Mn2＋-activated Ba9Sc2Si6O24 phosphor for white light emitting diodes

A single-phased silicate compound (Ba1-xCex)9(Sc1-yMny)2Si6O24 was prepared by solid-state reaction at high temperature. From powder X-ray diffraction (XRD) analysis, the formation of Ba9Sc2Si6O24 with an R3 space group was confirmed. In the photoluminescence spectra under ultraviolet (UV) ray excitation, the Ba9Sc2Si6O24:Ce3+,Mn2+ phosphor emits two distinctive color light bands: a blue one originating from Ce3+and a red one caused by Mn2+. The energy transfer process from Ce3+ to Mn2+ was confirmed, the critical radius as well as the transfer efficiency was calculated, and the energy transfer mechanism was discussed. In addition, the decay-time testing indicates that the energy transfer efficiencies from Ce(1) to Mn2+ and Ce(2) to Mn2+ are different. The emission chromaticity of Ba9Sc2Si6O24:Ce3+,Mn2+ phosphor could be tuned from blue to red by altering the Ce3+/Mn2+ concentration ratio.