Luminescence and energy transfer in Y2O3 CO-doped with Bi3+ and Eu3+

The emission spectra and decay times of the Y₂O₃ CO-doped with Bi³⁺ and Eu³⁺ have been investigated using site-selective excitation and time-resolved spectroscopy in the temperature range 8–296 K. Evidence for an energy transfer from Eu³⁺(S₆) to Eu³⁺(C₂) is given. The critical transfer distance R₀ = 8.6 Å was found from the decay curve.     

Structures and luminescence properties of Yb3＋ in the double perovskites Ba2YB＇O6 （B＇=Ta5＋, Nb5＋） phosphors

The Yb³⁺ doped Ba₂YB'O₆ (B'=Ta⁵⁺, Nb⁵⁺) were prepared by high temperature solid-state reaction method, their structures were determined by x-ray diffraction and refined by Rietveld method. The diffuse reflection absorption, excitation and emission spectra of Yb³⁺:Ba₂YB'O₆ (B'=,Ta⁵⁺, Nb⁵⁺) were measured at room temperature. Under the excitation of ultraviolet light, these phosphors exhibit broad charge transfer band emissions of TaO₆ or NbO₆ centre with large Stokes shift. The Yb³⁺ doped into these hosts are situated at Y³⁺ sites of cubic symmetry (O_h). The experimental energy levels of Yb³⁺ in Ba₂YTaO₆ and Ba₂YNbO₆ were determined by photoluminescence and diffuse reflection absorption spectra. Their wavefunctions and theoretical energy levels were obtained by diagonalising the Hamiltonian matrix. The experimental energy levels were fitted by Levenberg--Marquardt iteration algorithm to determine crystal field parameters. Then, the magnetic-pole transition line strengths of Yb³⁺:Ba₂YB'O₆(B'=Ta⁵⁺, Nb⁵⁺) from (²F_5/2)Γ₈^- to the low-energy states were calculated.     

Synthesis and laser patterning of Bi-doped Y3Fe5O12 crystals in germanosilicate glasses

New germanosilicate glasses giving the crystallization of yttrium iron garnet Y₃Fe₅O₁₂ (YIG) and Bi-doped YIG, 23Na₂O-xBi₂O₃-(12−x)Y₂O₃-25Fe₂O₃-20SiO₂-20GeO₂ (mol%), are developed, and the laser-induced crystallization technique is applied to the glasses to pattern YIG and Bi-doped YIG crystals on the glass surface. It is clarified from the Mössbauer effect measurements that iron ions in the glasses are present mainly as Fe³⁺. It is suggested from the X-ray diffraction analyses and magnetization measurements that Si⁴⁺ ions are incorporated into YIG crystals formed in the crystallization of glasses. The irradiations (laser power: 32-60 mW and laser scanning speed: 7 μm/s) of continuous wave Yb:YVO₄ fiber laser (wavelength: 1080 nm) are found to induce YIG and Bi-doped YIG crystals, indicating that Fe³⁺ ions in the glasses act as suitable transition metal ions for the laser-induced crystallization. It is suggested that YIG and Bi-doped YIG crystals in the laser irradiated part might orient. The present study will be a first step for the patterning of magnetic crystals containing iron ions in glasses.     

Luminescence Spectra of YGG：RE^3＋, Bi^3＋ （RE = Eu and Tb） and Energy Transfer from Bi^3＋ to RE^3＋

We investigate the luminescence properties of Bi^3＋ and RE^3＋ （RE = Tb or Eu） in a Y3Ga5O12 （YGG） host system. The additional doping of Bi^3＋ can enhance the luminescence of Th^3＋ or Eu^3＋ in this host. Energy transfer from Bi^3＋ to Tb^3＋ and Eu^3＋ is observed and the mechanism of energy transfer is investigated. Mechanism of energy transfer can be explained as electric multipole interaction since the Bi^3＋ emission band and Tb^3＋ or Eu^3＋ excitation band overlaps and the Bi^3＋ emission intensity decreases while the intensity of Tb^3＋ or Eu^3＋ increases with the increase of Tb^3＋ or Eu^3＋ concentration. Therefore, Bi^3＋ ion is a kind of efficient sensitizer to the Tb^3＋ and Eu^3＋ activators in the Y3Ga5O12 host.     

Co2+-Ti4+和Cu2+-Nb5+离子取代BaFe12O19单晶体中Fe3+离子的研究

本文对用Co²⁺-Ti⁴⁺和Cu²⁺-Nb⁵⁺离子取代BaFe₁₂O₁₉单晶体中Fe³⁺离子进行了研究,以Bi₂O₃作为助熔剂生长出了BaFe_12-2xCo_x²⁺Ti_x⁴⁺O₁₉(x=0;0.04;0.09;0.13;0.27和0.68)以及BaFe_12-x[Nb_1/3⁵⁺Cu_2/3²⁺]_xO₁₉(x=0;0.28;0.44和0.60)这两系列的单晶体,测定了100—300K温度范围内样品的磁化强度σ与单轴各向异性常数K₁,我们发现,对Co²⁺-Ti⁴⁺取代的样品,当x≤0.09时,其σ与K₁随x的增加而缓慢增加;当x>0.09时,其σ与K₁随x的增加而迅速降低,至x=1.1时,K₁变为零,对Nb⁵⁺-Cu²⁺取代的样品,其σ值在整个成份范围内基本保持不变,且有缓慢增加趋势;而K₁值则随x增加而单调下降,提出了取代离子在M型六角铁氧体中可能的分布模型来解释我们的结果。 关键词：     

Mise en évidence d'un échange électronique entre Fe2+ ET Fe3+ dans les oxydes rhomboédriques AFe2O4 par spectroscopie mossbauer DU57Fe

The ABB'O₄ rhomboedral oxides containing exclusively either Fe²⁺(InFeGe_0,5Zn_0,5O₄) or Fe³⁺(LuMg-FeO₄ and LuMnFeO₄) are investigated with Mössbauer spectroscopy, in their paramagnetic state.A similar study is made on two mixed oxides containing iron under its two oxidation states, with the $\text{Fe}{}^{\mathrm{2+}}\text{Fe}{}^{\mathrm{3+}}\text{= 2}$ and 1 (InFe_1,5Ga_0,5O₄ and InFe₂O₄) atomic ratio.Comparing the results, we have come to the conclusion that a fast electronic exchange between Fe²⁺ and Fe³⁺ takes place at room temperature. In this structure, point Fe²⁺ and Fe³⁺ are distributed on the same crystallographic site with the point symmetry C_3v. We show that neighbouring effects lower this local symmetry.     

Synthesis and characterization of monodisperse spherical core-shell structured SiO2@Y3Al5O12:Ce3+/Tb3+ phosphors for field emission displays

Nanocrystalline Y₃Al₅O₁₂: Ce³⁺/Tb³⁺ (average crystalline size 30 nm) phosphor layers were coated on non-aggregated, monodisperse and spherical SiO₂ particles by the sol-gel method, resulting in the formation of core-shell structured SiO₂@Y₃Al₅O₁₂:Ce³⁺/Tb³⁺ particles. X-ray diffraction, Fourier transform infrared spectroscopy, transmission electron microscopy, photoluminescence, cathodoluminescence spectra, as well as lifetimes were utilized to characterize the core-shell structured SiO₂@Y₃Al₅O₁₂:Ce³⁺/Tb³⁺ phosphor particles. The obtained core-shell structured phosphors consist of well-dispersed submicron spherical particles with a narrow size distribution. The thickness of the Y₃Al₅O₁₂:Ce³⁺/Tb³⁺ shells on the SiO₂ cores (average size about 500 nm, crystalline size about 30 nm) could be easily tailored by varying the number of deposition cycles (100 nm for four deposition cycles). Under the excitation of ultraviolet and low-voltage electron beams (1–3 kV), the core-shell SiO₂@Y₃Al₅O₁₂:Ce³⁺/Tb³⁺ particles show strong yellow-green and green emission corresponding to the 5d–4f emission of Ce³⁺ and ⁵D₄–⁷F _J (J = 6, 5, 4, 3) emission of Tb³⁺, respectively. These phosphors may have potential application in field emission displays.     

Identification of Fe4+ and Fe5+ charge-transfer photochromic absorption bands in SrTiO3

Optical absorption and the enhancement and bleaching of Fe³⁺ and Fe⁵⁺ electron paramagnetic resonance in SrTiO₃: Al measured as a function of wavelength and time show that the photochromic absorption bands are due to electron transfer from O^2- valence states to Fe⁴⁺ and Fe⁵⁺. They occur at 2.09 and 2.82 eV for Fe⁴⁺ and at 1.99 and 2.53 eV for Fe⁵⁺.     

Spectral properties of Ce3+ doped yttrium lanthanum oxide transparent ceramics

Ce3+-doped yttrium lanthanum oxide (Y0.9La0.1)2O3 transparent ceramics is fabricated with nanopowders and sintered in H2 atmosphere. The spectral properties of Ce:(Y0.9La0.1)2O3 transparent ceramics are investigated. There appear two characteristic absorption peaks of Ce3+ ions at 230 nm and 400 nm, separately. It is found that Ce3+ ions can efficiently produce emission at 384 nm from (Y0.9La0.1)2O3 transparent ceramic host, while the emission is completely quenched in Re2O3 (Re=Y, Lu, La) host materials.     

Calculations of the optical and EPR spectral data for Cr3+ ion in Y3Ga5O12 crystal from the complete diagonalisation method

The complete diagonalisation (of energy matrix) method is applied in this paper to calculate together the optical and electron paramagnetic resonance (EPR) spectral data for Cr³⁺ ion at the trigonal Ga³⁺ site of Y₃Ga₅O₁₂ crystal. The method is founded on the two-spin-orbit-parameter model where in addition to the contributions from the spin-orbit parameter of central dⁿ ion (i.e., one-spin-orbit-parameter model) in the traditional crystal field theory, those from the spin-orbit parameter of ligand ion via covalence effect is also considered. The calculated results propose that by using only four adjustable parameters, the 12 observed spectral data (nine optical band positions and three EPR parameters g_//, g_⊥ and D) in Y₃Ga₅O₁₂: Cr³⁺ are reasonably explained. The impurity-induced local lattice distortion of Cr³⁺ in Y₃Ga₅O₁₂ crystal is also estimated through the calculations. The results are discussed.     

Multisites Cr3+ in GGG and GSGG garnets

The emission and excitation spectra of Cr³⁺ -doped Gd₃Ga₅O₁₂ (GGG) and Gd₃Sc₂Ga₃O₁₂ (GSGG) are explained in the light of multisite effects. The situation is particularly complicated in the case of GSGG, where the different sites have²E energy levels near each other which overlap with the⁴A₂ ⁴T₂ absorption bands. The spectra obtained under selective excitations are interpreted on the multisite assumption.     

Synthesis and photoluminescence properties of MZr2(PO4)3:Eu3+; Bi3+ (M=Na; K) phosphors

A series of new red phosphors, MZr₂(PO₄)₃:Eu³⁺; Bi³⁺ (M=Na; K), were synthesized using the solidstate reaction method, and their photoluminescence spectra were measured. The MZr₂(PO₄)₃:Eu³⁺; Bi³⁺ (M=Na; K) phosphors were efficiently excited by an ultraviolet (UV; 395 nm) source, and showed intense orange-red emission at 595 nm. Further investigation of the concentration-dependent emission spectra indicated that the MZr₂(PO₄)₃:Eu³⁺; Bi³⁺ (M=Na; K) phosphors exhibit the strongest luminescence intensity when y = 0.01 in NaZr_2(0:95−y)(PO₄)₃:Eu_0.10³⁺, Bi_2y ³⁺ and y = 0.09 in NaZr_2(0.95−y)(PO₄)₃:Eu_0.10³⁺, Bi_2y ³⁺, whereas the relative PL intensity decreases with increasing Bi³⁺ concentration due to concentration quenching. The addition of Bi³⁺ widens the excitation band of NaZr_2(0.95−y)(PO₄)₃:Eu_0.10³⁺, Bi_2y ³⁺ around 320 nm, which provides the useful idea of broadening the excitation band around 300–350 nm to fit the ultraviolet chip.     

Emission and excitation spectra of Bi2Ge3O9:Eu3+

The emission and excitation spectra of the Bi₂Ge₃O₉:Eu crystal are observed at 77 K and 297 K. The spectra contain groups of sharp lines which are attributed to the transitions within 4f⁶ (Eu³⁺) configuration. The numbers of Stark splitting of terminal levels of transitions from ⁵D₀ and ⁷F₀ multiplets indicate that Eu³⁺ substitutes for Bi³⁺ in Bi₂Ge₃O₉. Tentative assignment of Stark levels of ⁷F_0-4 multiplets is made to crystal quantum numbers of C₃ symmetry which represents the site symmetry of Bi³⁺ in Bi₂Ge₃O₉. The following set of values of crystal field parameters of the C₃ point group is found to give the best overall agreement between the observed energy levels and the calculated levels: B²₀ = -533.84 cm^-1, B⁴₀ = 1085.99 cm^-1, Re(B⁴₃) = 327.57 cm^-1, Im(B⁴₃) = 75.209 cm^-1, B⁶₀ = 185.02 cm^-1, Re(B⁶₃) = - 68.475 cm^-1, Im(B⁶₃) = - 300.45 cm^-1, Re(B⁶₆) = 137.24 cm^-1 and Im(B⁶₆) = 882.29 cm^-1.     

Mössbauer spectra of Fe3+ and Fe2+ ions in hexagonal ferrite with w-structure

The hexagonal ferrite Fe₂W = BaFe₂²⁺Fe³⁺₁₆O₂₇ exhibits a sharp ⁵⁷Fe Mössbauer spectrum at 300 and 78 K. All seven sublattices in this complicated crystal structure are detected. Fast electron exchange between Fe²⁺ and Fe³⁺ ions gives rise to sharp lines and makes them indistinguishable. At 5 K the exchange is slow and the Fe²⁺ ions are detected from the presence of a weak subspectrum with broadened lines separated from the main spectrum of the Fe³⁺ ions. Analysis shows that the Fe²⁺ ions reside exclusively on one of the seven sublattices, which is occupied statistically by Fe²⁺ and Fe³⁺ ions in the ratio of 2 : 1. For SrFe²⁺₂Fe³⁺₁₆O₂₇ the situation is the same.     

Er3+/Ce3+共掺碲铋酸盐玻璃的制备及光谱特性提高研究

采用高温熔融退火法制备了系列 80TeO₂-10Bi₂O₃-10TiO₂-0.5Er₂O₃-xCe₂O₃ (x=0,0.25, 0.5,0.75,1.0 mol%)和(80-y) TeO₂-10Bi₂O₃-10TiO₂-yWO₃-0.5Er₂O₃-0.75Ce₂O₃ (y=3,6,9,12 mol%)的碲铋酸盐玻璃.测试了玻璃样品400-1700 nm范围内的吸收光谱, 975 nm抽运下的上转换发光谱和1.53 μm波段荧光谱, 以及808 nm激励下的Er³⁺离子荧光寿命和无掺杂玻璃样品的Raman光谱, 并结合Judd-Ofelt理论和McCumber理论计算了Er³⁺离子光谱参数.结果表明, 在掺Er³⁺碲铋酸盐玻璃中引入Ce³⁺离子进行Er³⁺/Ce³⁺共掺, 通过Er³⁺离子⁴I_11/2能级与Ce³⁺离子²F_5/2 能级间基于声子辅助的能量传递过程,可以有效抑制Er³⁺离子上转换发光并明显增强其 1.53 μm波段荧光;同时,在现有Er³⁺/Ce³⁺共掺玻璃组分基础上引入WO₃, 可进一步提高1.53 μm波段荧光并展宽其荧光发射谱. 研究结果对于获取优异光谱特性的宽带掺Er³⁺光纤放大器玻璃基质具有实际意义.     

Anisotropy of hexagonal ferrites with M,W and Y structures containing Fe3+ and Fe2+ as magnetic ions

The ferrimagnetic saturation moment and hexagonal anisotropy constant K₁ have been measured at 4K on a Zn₂Y single crystal and on polycrystalline BaFe²⁺₂W and SrFe²⁺₂W samples. The moment of Fe₂W is in agreement with a collinear spin coupling and with the known site occupation for the Fe²⁺ ions. The moment of Zn₂Y is 9% lower than the value for a collinear configuration.The uniaxial anisotropy of Fe²⁺ in hexagonal ferrites is discussed and compared with that of Co²⁺. No noticeable Fe²⁺ anisotropy is found in Fe₂W in contrast to LaM = LaFe²⁺Fe³⁺₁₁O₁₉, in which the Fe²⁺ anisotropy is strong. The difference is attributed to the symmetry difference of the sites occupied by the Fe²⁺ ions in both compounds. The current theory does not satisfactorily explain the anisotropy and quadrupole splitting of Fe²⁺ in LaM. From this it is concluded that admixing of ⁵E states and (or) the influence of a dynamical Jahn-Teller effect cannot be neglected.The dipole-dipole anisotropy is computed for the M, W and Y structure and some deviation from the literature data is found. Using these results, a mean anisotropy of 1.3 to 2.3 cm^?1 per Fe³⁺ ion is found for the three structures.     

Valence states of iron ions in nanostructured yttrium iron garnet Y3Fe5O12 studied by means of soft X-ray absorption spectroscopy

Nanostructured samples of yttrium iron garnet Y₃Fe₅O₁₂ obtained by plastic deformation method (high-pressure torsion) were studied with help of soft X-ray absorption spectroscopy using Fe 2p and O 1s spectra. Experimental spectra were compared with crystal field multiplet calculations for Fe ions. Some amount of Fe²⁺ ions in nanostructured Y₃Fe₅O₁₂ was found. The concentration of Fe²⁺ ions was found to be increased with the increase of the degree of plastic deformation.     

Bi离子掺杂GeO2-Al2O3-M(M=Na2O，BaO，Y2O3)玻璃的光学性质

用高温熔融法制备了Bi离子掺杂浓度为1mol%的GeO-B₂O₃-Na₂O (GBNB)，GeO₂-Al₂O₃-Na₂O(GANB)，GeO₂-Al₂O₃-BaO(GABB)和GeO₂-Al₂O₃-Y₂O₃(GAYB)玻璃.测定了样品玻璃的差热曲线、吸收、发射光谱及荧光衰减曲线.实验发现GBNB，GANB，GAYB，GABB的吸收边带逐步发生红移.由于这些吸收边带是由Bi³⁺的6s²电子到Bi⁵⁺ 6s⁰空轨道的跃迁引起.因此推断GBNB，GANB，GAYB，GABB玻璃中Bi⁵⁺离子的含量逐步增加.在GABB，GAYB，GANB三个样品中观察到发光中心约1220nm超宽带荧光发射.荧光强度从GABB，GAYB，GANB逐步减弱，荧光半高宽和荧光寿命逐步变小.这些超宽带的荧光归属为Bi⁵⁺离子的发光所致.从吸收与荧光光谱的变化，推断在GeO₂-Al₂O₃玻璃中引入BaO，Y₂O₃组分有利于Bi⁵⁺离子的形成.讨论了BaO，Y₂O₃化学组分对Bi离子在玻璃中的价态影响的内在机理. 关键词： 5+离子')" href="#">Bi⁵⁺离子 超宽带发光 吸收带 荧光寿命     

Luminescence of Fe3+ in single crystals of LiAl5O8

We have measured the luminescent properties of single crystals of LiAl₅O₈:Fe³⁺. In addition to a zero-phonon line due to Fe³⁺ in A-sites, we have observed another sharp fluorescent line at 699.2 nm which we assign to Fe³⁺ occupying B-sites. The excitation spectrum of the B-site Fe³⁺ shows characteristics similar to those of the A-site Fe³⁺ but are also shifted towards longer wavelengths. The spectra of the single crystals are compared with those of ordered and disordered powder samples.     

Comparison of theoretical and measured efficiencies for Tb3+ -activated garnet oxide phosphors

The relative CL efficiencies of two Tb³⁺ -activated garnet oxide phosphors, (Y_1?xTb_x)₃M₅O₁₂[M=Al, Ga], have been measured as a fucntion of Tb concentration and compared with predicted efficiencies calculated from a recently developed theoretical model. Agreement between theory and experiment is remarkably good, confirming the physical basis of the model and suggesting its useful predictive capacity for future phosphor development.