Crystal fields of Pr in LiYF4 under pressure

Fluorescence spectra of LiYF₄:Pr³⁺ have been measured between 12,000 and 22,000 cm⁻¹ under pressures up to 10 GPa. In total, 25 crystal field energy levels were obtained and used for the determination of free-ion and crystal field parameters under pressure. According to the nephelauxetic effect, the free-ion parameters decrease with increasing pressure. The relative decrease is larger for the Slater than for the spin-orbit coupling parameter. This behavior is consistent with former studies on Pr³⁺ in different crystals and can be explained by a special covalency model. According to an effective D_2d symmetry, five crystal field parameters B₀²(f,f), B₀⁴(f,f), B₄⁴(f,f), B₀⁶(f,f), and B₄⁶(f,f) are non-zero. The pressure-induced changes of these parameters have been determined up to the maximum pressure of 10 GPa. In order to improve the calculation of the crystal field levels, the configuration interactions with the 4f¹6p¹ configuration have been taken into account. The effect of these interactions are also analyzed under pressure and distinct improvements of the energy level calculations have been obtained.     

Radiation effects on luminescent and structural properties of YPO4: Pr3+ nanophosphors

ABSTRACT

YPO₄ phosphors doped with trivalent ion Pr³⁺ were prepared by sol–gel method and treated with different doses of gamma radiation, from 0.25 MGy to 4 MGy. Effects of radiation on morphology, structure and luminescent properties were analyzed. Also, the influence of radiation on the change in the color of the samples was examined. The color efficiency of powders was evaluated by colorimetric analysis (CIE and L * a * b system). It has been observed that powders change color under the influence of radiation, i.e. they pass from white to pinkish red. Also, it has been determined that the radiation affects morphology change, as the particle size increases with increasing of the radiation dose. With the increase in the radiation dose, the emission intensity of samples decreases. The structure remains almost unchanged after irradiation, and the intensity constantly decreases with increasing of dose.     

Theoretical studies of the spin-Hamiltonian parameters for the orthorhombic Pr4+ centers in Sr2CeO4 crystals

Theoretical studies of spin-Hamiltonian (SH) parameters associated with Pr⁴⁺ in Sr₂CeO₄ single crystals have been made by using the complete diagonalizing energy matrix method (CDM) for the 4f ¹ electronic configuration. The calculated results are in excellent agreement with the experimental data. The negative signs of the anisotropic g _i -factors and hyperfine structure constants A _i (where i = ∥ or ⊥) for the orthorhombic Pr⁴⁺ ion in Sr₂CeO₄ are suggested from the calculations. By comparing the results obtained by the CDM with the experimental data, one finds it is valid to interpret the SH parameters for 4f ¹ ions in crystals. The results are discussed.      

Lattice site dependent cathodoluminescence behavior and surface chemical changes in a Sr5(PO4)3F host

Eu activated Sr₅(PO₄)₃F phosphor powders have been subjected to the electron bombardment at 2 keV (10 μA) at an oxygen pressure of 1×10⁻⁶ Torr. The synthesized Sr₅(PO₄)₃F phosphor was identical to the hexagonal apatite structure, with the Sr present at two different sites C_s (S1) and C₃ (S2) in the Sr₅(PO₄)₃F host, as inferred from the crystallographic study. Cathodoluminescence (CL) and Auger electron spectroscopy of the phosphor excited by the same electron beam were used to monitor changes in the surface state during prolonged electron bombardment. A direct correlation between the surface reactions and the degradation of the CL brightness was observed. Both C and F were depleted from the surface during electron bombardment. The postulated mechanism for the electron stimulated chemical reactions on the phosphor surface is electron beam dissociation of molecular species to atomic species, which subsequently react with C to form volatile compounds CO₂, CH₄, etc. and with Sr₅(PO₄)₃F to form a non luminescence layer of metal oxides of Sr and P.     

Tm3+/Yb3 :LiYF4单晶的高效近红外量子剪裁及其在光伏电池中的应用

采用改进的坩埚下降法成功地生长了Tm/Yb共掺氟化钇锂单晶. 该单晶体具有每吸收一个蓝色光子并能发射出2个1000 nm近红外光子的下转换发光效应. 测定了样品的激发光谱、发射光谱和荧光衰减曲线. 在465 nm蓝光激发下观察到由Yb³⁺：²F_5/2→²F_7/2能级跃迁所致的960～1050 nm 波段的发射带,此发光带源于Tm³ 对Yb³ 离子的能量下转换过程. 应用Inokuti-Hirayama模型,研究了晶体的能量转换过程,结果表明Tm³ 向Yb³ 的能量传递是一个电偶极子相互作用机制过程. 当Tm³ 与Yb³ 离子的掺杂浓度为0.49mol%与5.99mol%时,单晶的量子剪裁效率达到最大值167.5%.     

ECR-PECVD制备Si3N4薄膜的光学特性研究

本文研究了ECR-PECVD制备的Si₃N₄薄膜的光学特性.得到的Si₃N₄薄膜具有光致发光效应,在280℃沉积制备的Si₃N₄薄膜的光致发光波长为400nm,具有较好的单色性.测试分析了Si₃N₄薄膜对可见光、红外光具有较高的透射性能,Si₃N₄薄膜可作为红外光的增速减反射膜.     

Electron paramagnetic resonance of Mn2+ and Gd3+ in Pr2Zn3(NO3)12.24 H2O single crystals

The electron paramagnetic resonance of Mn²⁺ and Gd³⁺ doped in Pr₂Zn₃(NO₃)₁₂.24H₂O single crystals has been studied at X-band. Mn²⁺ substitutes for two Zn²⁺ sites, while Gd³⁺ substitutes for single type of Pr³⁺ sites. The spin-Hamiltonian analysis of the EPR spectra is presented at 298 K as well as 77 K.     

Cr4+:Ca2GeO4激光晶体生长及结构表征

采用助熔剂法,以CaCl₂为助熔剂,生长Cr⁴⁺ :Ca₂GeO₄新型近红外可调谐激光晶体.通过X射线衍射(XRD)、激光Raman光谱、X射线光电子能谱(XPS)等方法对晶体进行结构表征.结果表明,得到的晶体为单斜晶系镁橄榄石结构的低温γ-Cr⁴⁺ :Ca₂GeO₄单晶,晶格参数为a=5.3209 (1 =0.1 nm)     

TSL, OSL and ESR studies in ZnAl2O4:Tb phosphor

ZnAl₂O₄:Tb phosphor was prepared by combustion synthesis. ZnAl₂O₄:Tb exhibits three thermally stimulated luminescence (TSL) peaks around 150, 275 and 350 °C. ZnAl₂O₄:Tb exhibits optically stimulated luminescence (OSL) when stimulated with 470 nm light.Electron spin resonance (ESR) studies were carried out to identify defect centres responsible for TSL peaks observed in ZnAl₂O₄:Tb. Two defect centres are identified in irradiated ZnAl₂O₄:Tb phosphor and these centres are assigned to V and F⁺ centres. V centre appears to correlate with the 150 °C TSL peak, while F⁺ centre could not be associated with the observed TSL peaks.     

Spectroscopy of defects in irradiated alpo 4 and GaPO 4 crystals

The time-resolved luminescence spectra in energy region of 2.0-6.0 v eV, as well as the excitation spectra (4-35 v eV), reflectivity and the decay kinetics were studied at T =10 v K and 295 v K using selective vacuum ultraviolet excitation in nominally pure crystals as well as crystals with intrinsic defects and radiation defects induced by fast electrons.     

Study of the d-f Emission,and f-d Ground-State and Excited-State Absorption of Nd3+ in Crystals Using the Simple Model

The simplified model for 4f-5d transitions is applied to obtain the line strengths for emission, ground-state absorption and excited states absorption involving 4f-5d transitions of Nd³⁺ in crystals. The results are host independent for the usual case where 5d crystal-field interaction can be considered as strong, in the sense that the calculated 5d-4f emission relative line strengths will be the same for Nd³⁺ in any host. Also the calculated 4f-5d absorption line strengths can be grouped by the 5d crystal-field components. For each 5d crystal-field component, the group of absorption line strengths for different 4f²5d transition final states forms a pattern independent of the 5d crystal-field component and the host. For practical cases, due to strong but still limited 5d crystal-field splitting, the transitions to different 5d crystal-field components may overlap each other. The theoretical results are used to interpret available experimental data.     

Precipitate synthesis of BaMoO4 and BaWO4 nanoparticles at room temperature and their photoluminescence properties

The uniform BaMoO₄ and BaWO₄ nanoparticles (NPs) have been successfully synthesized by solution route – the direct precipitation of Ba(NO₃)₂ and Na₂MO₄ (M = Mo and W) in ethylene glycol under 24 h stirring. The XRD patterns and SEM images proved that the products were tetragonal structured BaMoO₄ and BaWO₄ with uniform round nanoparticles. Shape, average particle size and particle-size distribution of products were analyzed by TEM – showing the round nanoparticles with the average size of 31.52 ± 4.65 nm for BaMoO₄, and 59.77 ± 9.61 nm for BaWO₄. The room temperature photoluminescence (PL) indicated that the products have strong blue emission centered at 441 nm – excited with 280 nm wavelength for BaMoO₄ NPs, and strong violet emission centered 378 nm – excited with 344 nm wavelength for BaWO₄ NPs. These PL behaviors attributed the existence of intrinsic transitions in the [MO₄]^2-$[{\text{MO}}_4{]}^{2-}$ (M = Mo and W) tetrahedrons of their crystal lattices.     

DSC study of superionic phase transition in (NH4)4H2(SeO4)3 single crystals

DSC and complex impedance studies of the protonic conductor (NH₄)₄H₂(SeO₄)₃, which undergoes a superionic phase transition of first order at T_s = 378 K show that the activation energy of ionic conductivity d(lg σ)/dt and the ordering enthalpy ΔC_p of the crystal are proportional: d(lg σ)/dT = XΔC_p/RT_s + const, as found for MAg₄I₅ crystals undergoing a second-order superionic phase transition. Thus the short-range order environment of the species involved in fast-ion transport plays the main role in the superionic phase transition. This is also supported by the value of the entropy change at T_s, ΔS = 43 J/mole·K. A new metastable phase was found to be induced on heating the (NH₄)₄H₂(SeO₄)₃ crystal above T_s.     

VUV luminescence of Er<Superscript>3+</Superscript> ions in LiYF<Subscript>4</Subscript> and BaY<Subscript>2</Subscript>F<Subscript>8</Subscript> crystals

Vacuum ultraviolet luminescence of Er³⁺ ions in LiYF4 and BaY₂F₈ crystals has been investigated. It is revealed that under excitation by 193 nm radiation from an ArF excimer laser the interconfigurational 5d–4f radiative transitions in Er³⁺ ions are observed. It is shown that from the LiYF₄:Er crystal only the spin-forbidden luminescence (λ = 165 nm) is detected, whereas both the spin-forbidden (λ = 169 nm) and spin-allowed (λ = 160.5 nm) components are observed from the BaY₂F₈:Er crystal.     

花状NaY(MoO4)2的合成和(MoO4)2:Eu3+的光学性质

用微波辅助水热-煅烧法成功合成了花状NaY(MoO₄)₂颗粒,用XRD、XPS、FESEM进行了表征,提出了花状NaY(MoO₄)₂颗粒可能的形成机理. 采用相同的方法合成了NaY(MoO₄)₂:Eu³⁺荧光体,该荧光材料在612 nm处有一个强的发射峰,可用作白色发光二极管的红色磷光剂. 此外,微波辅助水热-煅烧法可能发展成为制备其他花状稀土钼酸盐的有效途径.     

Native defects and Pr impurities in orthorhombic CaTiO3 by first-principles calculations

Formation energies of native defects and Pr impurities in orthorhombic CaTiO₃ are explored using the first-principles calculations. The Ca vacancy (V_Ca), Ti vacancy (V_Ti) and Ca antisite (Ca_Ti) are found to be energetically preferable. The Ti antisite (Ti_Ca) and O vacancy (V_O) are not energetically favorable in the wide range of Fermi level. In Pr-doped CaTiO₃, Pr substituting for Ca (Pr_Ca) is likely to form under condition A in which CaTiO₃ is in equilibrium with CaO and O₂. Under condition B (TiO₂, CaTiO₃ and O₂ are in equilibrium), Pr_Ti defect is energetically preferable depending on the Fermi levels. Several native defects and the two sites of Pr impurities in CaTiO₃ are coincided with several different defects in Pr-doped CaTiO₃ reported in the literature. Based on the present calculations, we can elucidate that the Ca deficiency design of the traditional formula Ca_1−xV_Ca(x/2)Pr_xTiO₃ is not the best for efficient red photoluminescence, which is realized via the experimental measurements.     

Spectroscopy of Sm3+ activator centers in Ca3Ga2Ge4O14 single crystals

Results of investigations of spectroscopic properties of Ca₃Ga₂Ge₄O₁₄ single crystals activated with Sm³⁺ ions are reported. It is shown that Sm³⁺ ions in Ca₃Ga₂Ge₄O₁₄ form a type of activator quasicenter whose nature is associated with disordering of the matrix. I. Franko Lvov State University, 50, Dragomanov St., Lvov, Ukraine. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 65, No. 2, pp. 296–298, March–April, 1998.     

Normal Coordinates Analysis for The M(NH3)2+ 4 Complex Ions in D4h and Td Symmetries. Simplified Molecular Models

A normal coordinates analysis for the M(NH₃)²⁺ ₄ complex ions in T_d symmetry (M = Zn, Cd, Co) and in D_4h symmetry (M = Cu, Pd, Pt) has been undertaken on the basis of a General Valence Force Field (GVFF), using simplified molecular models. Throughout the course of the present work, we have relaxed the point mass approximation for the NH₃-ligands in order to investigate, on a quantitative basis, some relevant ligand - framework coupling vibrations. The simplest molecular model able to accomplish this purpose is to treat the ammino group, in a linear ligator approximation. We show that these model calculations provide a satisfactory set of vibrational frequencies as well as consistent sets of force constants.     

Numerical simulation of end-pumped CW Nd^3＋：GdVO4 laser at 1063 nm

A theoretical model to simulate an end-pumped CW Nd^3＋：GdVO4 laser at 1063 nm is presented. Its essence is to use the propagation equations to demonstrate the spatial evolutions of the pump and the laser powers in the cavity, hence it is applicable to both low and high gain lasers. The simulation results obtained by this model are in good agreement with the experimental observations reported in the literature for a Ti：sapphlre-pumped Nd^3＋：GdVO4 laser. Moreover, some parameters, such as the reflectivity of output coupler, the spot size of laser beam and the crystal length, are discussed with a view to optimizing the laser performance.