Wenjun Wang

Preferential occupancy of Eu3+ and energy transfer in Eu3+ doped Sr2V2O7, Sr9Gd(VO4)7 and Sr2V2O7/Sr9Gd(VO4)7 phosphors

The vanadate-based phosphors Sr2V2O7:Eu3+ (SV:Eu3+), Sr9Gd(VO4)7:Eu3+ (SGV:Eu3+) and Sr9Gd(VO4)7/Sr2V2O7:Eu3+ (SGV/SV:Eu3+) were obtained by solid-state reaction. The bond-energy method was used to investigate the site occupancy preference of Eu3+ based on the bond valence model. By comparing the change of bond energy when the Eu3+ ions are incorporated into the different Sr, V or Gd sites, we observed that Eu3+ doped in SV, SGV or SV/SGV would preferentially occupy the smaller energy variation sites, i.e., Sr4, Gd and Gd sites, respectively. The crystal structures of SGV and SV, the photoluminescence properties of SGV:Eu3+, SV, SGV/SV and SGV/SV:Eu, as well as their possible energy transfer mechanisms are proposed. Interesting tunable colours (including warm-white emission) of SGV/SV:Eu3+ can be obtained through changing the concentration of Eu3+ or changing the relative quantities of SGV to SV by increasing the calcination temperature. Its excitation bands consist of two types of O2− → V5+ charge transfer (CT) bands with the peaks at about 325 and 350 nm respectively, as well as f–f transitions of Eu3+. The obtained warm-white emission consists of a broad photoluminescence band centred at about 530 nm, which originates from the O2− → V5+ CT of SV, and a sharp characteristic spectrum (5D0–7F2) at about 615 and 621 nm.

Eu3+/2+ co-doping system induced by adjusting Al/Y ratio in Eu doped CaYAlO4: preparation, bond energy, site preference and 5D0–7F4 transition intensity

CaY1−xAl1+xO4:2%Eu (x = 0, 0.1, 0.2) phosphors have been synthesized via a solid-state reaction process. XRD patterns indicate that they are pure phase. The photoluminescence properties of the CaY1−xAl1+xO4:2%Eu phosphors exhibit both the blue emission of Eu2+ (4f65d1–4f7) and red-orange emission of Eu3+ (5D0–7F1,2,3,4) under UV light excitation, which showed that the Eu3+/2+ co-doping system was obtained by adjusting the Al/Y ratio. Eu3+ ions can be reduced to Eu2+ ions when the Al/Y ratio was changed. In this work, the bond energy method was used to determine and explain the mechanism of the site occupation of Eu ions entering the host matrix. Also, the emission spectrum showed an unusual comparable intensity 5D0–7F4 transition peak. The relative intensity of 5D0–7F2 and 5D0–7F4 can be stabilized by changing the relative proportions of Al3+ and Y3+. Furthermore, this was explained by the J–O theory.

The Bond-Energy Method in Site Occupancy and Property of High Concentration Eu3+ in Sr2CeO4 Phosphors

The low concentration of Eu3+ doped Sr₂CeO₄ phosphors has been widely studied in recent years and in this paper, we researched the properties of high concentration Eu3+ doped in Sr₂CeO₄. The Sr₂Ce(1-x)Eu4-x/2 (x = 0, 1%, 10%, 20%) phosphors were obtained by traditional solid-state reaction. Photoluminescence (PL) spectra are characterized the property of samples. PL spectra illustrate that the concentration of Eu3+ increased, the intensity of 5D0-7F1, 5D0-7F₂ increased and intensity of Sr₂CeO₄ host emission intensity was decreased. The phenomenon can be ascribed to the energy transfer from Ce4+ to Eu3+. When the concentration of Eu3+ is 20%, the completely red emission can be obtained even if no other ions are doped under the excitation wavelength of 350 nm, it is proved that Eu3+ occupied Ce sites rather than Sr site in Sr₂CeO₄ samples. The conclusion we make is due to the value of |ΔEEuCe-O| and |ΔEEuSr-O| calculated by bond-energy method, the smaller the value, the easier it is for the doped ions Eu3+ to enter the site.

The Bond-Energy Method in Site Occupancy and Property of Eu3+ Doped in SrAl2B2O7 Phosphors

The SrAl₂B₂O7:1%Eu3+ phosphors were obtained by solid-state reaction. Photoluminescence (PL) spectra are characterized the property of samples, and under the excitation of 394 nm, the sharp emission lines of SrAl₂B₂O7:1%Eu3+ can be assigned to Judd-Ofelt transitions (5D0-7FJ) of Eu3+, which are 5D0-7F1, 5D0-7F₂, 5D0-7F₃, and 5D0-7F₄. The bond energy method is used to determine the site occupancy, and the occupancy of Eu3+ can be determined by comparing the deviation of its bond energy in different locations at Sr2+, Al3+ and B3+ sites. Theoretical calculation result indicates that Eu3+ would preferentially occupy the smaller energy variation sites Sr2+.

Chemical bond parameters, bond energy and the local crystal sites of Eu3+ in Ca5(BO3)3F:1% Eu3+ phosphor

The local crystal sites occupied by Eu3+ in Ca5(BO3)3F:1% Eu3+ phosphor were investigated experimentally and theoretically. Ca5(BO3)3F:1% Eu3+ was synthesized by high-temperature solid-state method in air. The crystal structure and optical properties of the phosphor were studied by X-ray powder diffraction and photoluminescence, respectively. Two different O2− → Eu3+ CT broad bands with the peaks at 266 and 283 nm in Ca5(BO3)3F:1% Eu3+ were detected, indicating the Eu3+ sites occupied Ca2 and Ca1, respectively. The different sharp f–f emission spectra under the excitation of 283 and 266 nm proved that there are two different local lattice environments around Eu3+ existing in Ca5(BO3)3F:1% Eu3+. Environmental factor he, the standard deviation of environmental factor (EFSD) and the bond energy were used to illustrate and explain the site occupancy mechanism of Eu3+ into the host lattice. By comparing the intensity ratios of 5D0 → 7F2 transition to the 5D0 → 7F1 transition, I(5D0/7F2)/I(5D0/7F1) of Eu3+ at Ca2 (7.381) was found to be 2.5 times stronger than that of Eu3+ at Ca1 site (2.933). was calculated to analyze the I(5D0/7F2)/I(5D0/7F1) value. On the basis of the bond valence model, a bond-energy method was used to study the occupancy of the Eu ion, which indicated that the preferential sites of Eu ion occupancy in the Ca5(BO3)3F are the Ca2 and Ca1 sites. All three theoretical calculation results are consistent with each other.

The size effect to O2−-Ce4+ charge transfer emission and band gap structure of Sr2CeO4

Sr2 CeO4 phosphors with different crystalline sizes were synthesized by the sol-gel method or the solid-state reaction. Their crystalline size, luminescence intensity of O2- -Ce4+ charge transfer and energy gaps were obtained through the characterization by X-ray diffraction, photoluminescence spectra, as well as UV-visible diffuse reflectance measurements. An inverse relationship between photoluminescence (PL) spectra and crystalline size was observed when the heating temperature was from 1000°C to 1300°C. In addition, band energy calculated for all samples showed that a reaction temperature of 1200°C for the solid-state method and 1100°C for sol-gel method gave the largest values, which corresponded with the smallest crystalline size. Correlation between PL intensity and crystalline size showed an inverse relationship. Band structure, density of states and partial density of states of the crystal were calculated to analyze the mechanism using the cambrige sequential total energy package (CASTEP) module integrated with Materials Studio software.

Fitted peaks data of O 2− –V 5+ charge transfer bands and R/O data of Eu 3+ doped Ca(VO 3 ) 2 and Ca 3 (VO 4 ) 2

Data presented in this article are related to the research article entitledO2−–V5+charge transfer band, chemical bond parameters and R/O of Eu3+doped Ca(VO3)2and Ca3(VO4)2: A comparable study[ing Li, Yu Pan, Wenjun Wang, Zihao Wen, Xuanxi Leng, Qi Wang, Liqun Zhou, Haibing Xu, Qinghua Xia, Li Liu, Hongping Xian, Xiaoguang Liu]. The data present the fitting results of the broad excitation spectra of Ca(VO3)2:1%Eu and Ca3(VO4)2:1%Eu using the Gaussian model, the O/R values using the experimental PL emission results. The data compares the optimized cell parameters for Ca(VO3)2: 1%Eu and Ca3(VO4)2:1%Eu through the CASTEP geometry optimization with their initial cell parameters.