Magnetic properties of Nd0.9Dy0.1Fe3(BO3)4

The magnetic properties of trigonal Nd_0.9Dy_0.1Fe₃(BO₃)₄ substituted compound with the competitive Nd-Fe and Dy-Fe exchange interactions have been investigated. It has been shown that in Nd_0.9Dy_0.1Fe₃(BO₃)₄ a spontaneous spin-reorientation transition from an ease-axis state to an easy-plane occurs near 8 K. Anomalies of the magnetization curves are observed in a spin-flop transition induced by the magnetic field B‖c. The calculations were performed using a molecular-field approximation and a crystal-field model for the rare-earth subsystem. Extensive experimental data on the magnetic properties of Nd_0.9Dy_0.1Fe₃(BO₃)₄ have been interpreted and good agreement between theory and experiment has been achieved using the obtained theoretical dependences.     

Time-resolved site-selection spectroscopy studies of NdAl3(BO3)4 crystals

A pulsed, tunable dye laser was used to selectively excite Nd³⁺ ions in nonequivalent crystal field sites in NdAl₃(BO₃)₄ crystals and energy transfer between ions in different types of sites was studied by monitoring the time evolution of the fluorescence spectrum. The results show that the energy transfer rate varies as t^{$\text{-1}\text{2}$} and increases with temperature. The predictions of various models of phonon-assisted energy transfer are compared to the results.     

Energy levels and crystal-field analysis of Tm in YAl3(BO3)4 crystals

The electronic structure of the Tm³⁺ in YAl₃(BO₃)₄ crystals has been investigated by means of low temperature absorption and emission spectroscopy in the 5000-30,000 cm⁻¹ range. The assignment of the lines composing the observed manifolds to transitions between the Stark levels of Tm³⁺ is complicated by the presence of extra features having different origins. The energy levels scheme of the doping ion has been compiled after a careful analysis of the spectra by reproducing the observed transitions by means of theoretical calculations based on a Hamiltonian, including the free ion and the crystal field (CF) terms. The agreement between experimental and calculated energy values was reasonably good, the overall r.m.s. deviation being 16 cm⁻¹. The resulting CF parameters have been tabulated and compared with those reported in literature for other rare earth ions doped in YAB. The analysis of trends observed along the lanthanide series evidences some inconsistencies and the necessity of a systematic investigation of these systems.     

Investigation of the iron borates DyFe3(BO3)4 and HoFe3(BO3)4 by the method of Er spectroscopic probe

Temperature-dependent high-resolution optical spectra of the Er³⁺ probe ion in DyFe₃(BO₃)₄ and HoFe₃(BO₃)₄ are reported. The data provide the temperature of magnetic ordering and direction of the Fe³⁺ magnetic moments. Both compounds order magnetically at TN=39±1 K$T_{\mathrm{N}}=39\pm 1\text{ K}$. The magnetic structure of DyFe₃(BO₃)₄ is of the easy-axis type, while that of HoFe₃(BO₃)₄ is of the easy-plane type. The role of anisotropic interactions between the iron and the rare-earth subsystems is discussed.     

Terahertz spectroscopy of multiferroic EuFe3(BO3)4

The terahertz spectra of a rare-earth iron borate with the huntite structure are obtained for the first time. We study the low-temperature (4.0–90 K) α-polarized transmittance spectra of the EuFe₃(BO₃)₄ single crystal in the region 0.9–6.0 THz. Pronounced shifts of phonon frequencies and appearance of new phonon modes at the temperature _TS=58 K$T_S=58\text{K}$ of the R32→P₃₁21$R32\to P{3}_{1}21$ structural phase transition are observed. Additional shifts of phonon frequencies occur at the temperature _TN=34 K$T_N=34\text{K}$ of the magnetic ordering of the Fe subsystem, thus evidencing the spin–phonon coupling in this multiferroic material.     

Antiferromagnetic resonance in ferroborate NdFe3(BO3)4

The AFMR spectra of the NdFe₃(BO₃)₄ crystal are measured in a wide range of frequencies and temperatures. It is found that by the type of its magnetic anisotropy the compound is an “easy-plane” antiferromagnet with a weak anisotropy in the basal plane. The effective magnetic parameters are determined: anisotropy fields H_a1=1.14 kOe and H_a2=60 kOe and magnetic excitation gaps Δν₁=101.9 GHz and Δν₂=23.8 GHz. It is shown that commensurate-incommensurate phase transition causes a shift in resonance field and a considerable change in absorption line width.At temperatures below 4.2 K nonlinear regimes of AFMR excitation at low microwave power levels are observed.     

Optical amplification properties of Dy3+-doped Gd2SiO4, Lu2SiO5 and YAl3(BO3)4 single crystals

Comparative investigation of the optical amplification properties of dysprosium doped Gd₂SiO₅, Lu₂SiO₅ and YAl₃(BO₃)₄ single crystals was performed in a pump-and-probe experiment. High power laser pulses at 475 nm were used as the pump source in order to strongly populate the ⁴F_9/2 level of the Dy³⁺ ions due to ground state absorption. Low signal beam cw radiation at 574 nm was used as the probe beam to stimulate the emission associated with the ⁴F_9/2→⁶H_13/2 electronic transition of the Dy³⁺ ions. The process was modelled as a three levels system, and their populations were analysed and simulated in order to study the gain dynamics. Positive optical gain was observed and compared in these crystals. These results confirmed that among the systems studied the Dy³⁺-doped YAl₃(BO₃)₄ single crystal can be considered as a good candidate to develop an optical amplifier employing the ⁴F_9/2→⁶H_13/2 transition at around 574 nm which is the first step to consider as laser active media.     

Yb and Yb-Eu luminescent properties of the Li2Lu5O4(BO3)3 phase

The luminescence of Yb³⁺ in the oxyborate Li₂Lu₅O₄(BO₃)₃ is reported. At low temperature, in addition to the usual ytterbium infrared emission, this phosphor presents an emission in the ultraviolet () which corresponds to the transition from the charge transfer state (O-Yb) to the 4f levels of Yb³⁺. The temperature quenching Tq50% is equal to 120 K. The infrared emission studied at room temperature is located between 950 and 1100 nm.Europium emission quenching in the Li₂Yb₅O₄(BO₃)₃ phase is related to Eu→Yb transfer by cross-relaxation. The reverse Yb→Eu transfer by cooperative sensitization is highlighted in the codoped Li₂Lu₅O₄(BO₃)₃ compound.     

Growth and laser properties of Nd:Ca4YO(BO3)3 crystal

Nd:Ca₄YO(BO₃)₃ (Nd:YCOB) crystal was grown by the Czochralski method, and its structure was measured by using a four circle X-ray diffractometer. The transparent spectrum from 200 to 2600 nm was measured at room temperature. The fluorescence spectrum near 1.06 μm showed that the main emission wavelength of Nd:YCOB crystal was centered at 1060.8 nm. Laser output at 1.06 μm has been demonstrated when it was pumped by a Ti:sapphire laser at the wavelength of 794 nm, the highest output power was 68 mW under pumping power of 311 mW, the pumping threshold was 163 mW and slope efficiency was 46.9%. The self-frequency doubled green light has been observed when it was pumped by a Ti:sapphire or a laser diode (LD). A 14.5 mm Nd:YCOB crystal sample cut at (θ, φ)=(90°, 33°) was used for type I second-frequency generation (SHG) of the 1.06 μm laser pulse. The SHG conversion efficiency was 22%.     

Spectroscopic properties of Tm -doped Ba3Gd2(BO3)4 crystal

crystal with the size up to Φ 13 mm×44 mm was grown successfully by the Czochralski technique and its optical properties were presented. The absorption cross-section and emission cross-section were presented. Also, the potential laser gain near 1.9 μm was investigated. In the framework of the Judd-Ofelt (J-O) theory, the intensity parameters were calculated to be: Ω₂=11.375×10⁻²⁰ cm², Ω₄=5.077×10⁻²⁰ cm² and Ω₆=6.524×10⁻²⁰ cm². The spectroscopic parameters of this crystal such as the oscillator strengths, radiative transition probabilities, radiative lifetime as well as the branching ratios were calculated, too. This crystal is promising as a tunable infrared laser crystal.     

Spectroscopic and crystal field studies of (Ce,Gd)Sc3 (BO3)4:Cr crystals

Complex spectroscopic studies of (Ce,Gd)Sc₃(BO₃)₄:Cr³⁺ (CSB:Cr³⁺) crystals (crystal growth, absorption and luminescence spectroscopy, crystal field calculations, analysis of the radiative and non-radiative decays) are presented. The main results of the paper include calculations of crystal field parameters and energy level scheme for Cr³⁺ at distorted octahedral Sc³⁺ sites, evaluation of the Huang-Rhys factor, effective phonon frequency, zero-phonon line energy, and parameters of radiative and non-radiative decays. Comparison with experimental results and other literature data is discussed. A very unusual value of the frequency factor (related to the non-radiative processes) is explained as being due to heterodesmic nature of chemical bonds in the CSB crystal. Cr³⁺-doped CSB crystals (with Cr³⁺ concentration 5.1×10¹⁹ cm⁻³ or 1%) are suggested as promising candidates for potential applications as active media for solid state lasers.     

Luminescence properties of novel NaBa4(BO3)3:Ce, Eu phosphors

Novel Eu³⁺, Ce³⁺ activated NaBa₄(BO₃)₃ phosphors were synthesized by solid-state reactions. The excitation spectrum of NaBa₄(BO₃)₃:Ce³⁺ consists of an intense band peaking at 350 nm and a weak band in the higher energy side, and the emission spectrum exhibits a blue band with a maximum at about 420 nm. The Eu³⁺ emission in NaBa₄(BO₃)₃ consists of the transitions from ⁵D₀ to ⁷F_J, and the excitation spectrum consists of broad excitation band peaking at 270 nm and some intense narrow lines. The optimum doped concentration, the critical distance of the concentration quenching, and the fluorescence lifetime have also been investigated.     

Optical constants of Cu(In0.7Ga0.3)5Se8 and Cu(In0.4Ga0.6)5Se8 crystals

Variable angle spectroscopic ellipsometry has been applied to characterize the optical constants of bulk Cu(In_0.7Ga_0.3)₅Se₈ and Cu(In_0.4Ga_0.6)₅Se₈ crystals grown by the Bridgman method. The spectra were measured at room temperature over the energy range 0.8-4.4 eV. Adachi’s model was used to calculate the dielectric functions as well as the spectral dependence of complex refractive index, absorption coefficient, and normal-incidence reflectivity. The calculated data are in good agreement with the experimental ones over the entire range of photon energies. The parameters such as strength, threshold energy, and broadening, corresponding to the E₀, E_1A, and E_1B interband transitions, have been determined using the simulated annealing algorithm.     

Study on the second-harmonic-generation of GdCa4O(BO3)3 crystals along various phase-matching directions

In this paper, the theoretical calculations of d_eff of GdCa₄O(BO₃)₃ (GdCOB) along various phase-matching (PM) directions are reported. It is shown that the maximum d_eff is out of the main planes and the d_eff in the range of (0<θ≤90, 90<φ≤180) are larger than that in the range of (0<θ≤90, 0≤φ≤90). The PM direction along (θ=66.8, φ=132.6) for GdCOB crystal has the largest d_eff. Second-harmonic-generation (SHG) experiments were performed on GdCOB crystal along various PM directions. The results show that in GdCOB crystal, the intracavity SHG conversion efficiency is 27.6% along the PM direction (θ=66.8, φ=132.6) which is larger than that along PM directions in XY and XZ main planes, which are in good agreement with the theoretical calculations. The continuous-wave (cw) green laser output power is 1.22 W when LD pump power is 10 W in the Nd:YVO₄/GdCOB laser.     

Eu3+/Dy3+共掺Sr3Y2(BO3)4荧光粉的发光性质研究

稀土掺杂发光材料一直是科研领域研究的热点,被广泛应用于白光LED、温度传感、显示显像、新能源和激光等领域。基质的结构对于稀土离子光致发光特性有非常重要的影响,在众多发光基质材料中,硼酸盐具有透光范围宽、光学损伤阈值高、较好的热稳定性和化学稳定性等优点。碱土-稀土金属硼酸盐Sr₃Y₂(BO₃)₄具有出色的光学性能,对其发光性能的研究具有重要意义。稀土离子Eu³⁺具4f⁶电子层,是一种典型的下转换发光中心离子,常被选作红色发光材料的激活剂。Dy³⁺具4f⁹电子层,也是一种典型的下转换发光中心离子,在紫外光激发下,在蓝色光区和橙色光区有较强的荧光发射。采用高温固相法合成了Sr₃Y₂(BO₃)₄∶Eu³⁺/Dy³⁺荧光粉,通过XRD和SEM对样品的结构和形貌进行了表征,XRD结果表明,1 0...     

EPR and optical properties of KYb(WO4)2 and KTb0.2Yb0.8(WO4)2 single crystals

Well oriented KYb(WO₄)₂ and KTb_0.2Yb_0.8(WO₄)₂ single crystals have been investigated for their magnetic and optical properties using the Raman and EPR techniques. The registered EPR signal is dominated by three lines ascribed to ytterbium ions: one main and two satellites. Tb ions, although non-paramagnetic, distinctly modify magnetic properties of the KYb(WO₄)₂ single crystal. Basic parameters of the spin Hamiltonian, including Zeeman and hyperfine terms (g and A matrices) as well the spatial orientation between principal and crystallographic axes systems were determined for both crystals.     

Linear and nonlinear optical properties of Ca3(VO4)2

Single crystals of Ca₃ (VO₄)₂ have been grown by the Czochralski method. The refractive indices show that the crystals are phasematchable between 1.72 μm and 2.94 μm with favourable values for acceptance angle and spectral width of the incident laser beam in the entire phasematching range. The nonlinear optical coefficients have been measured by the Maker fringe method at a fundamental wavelength of 1.064 μm. They are comparable to those of KDP. Thus the crystals are potentially useful for frequency conversion of broadband or tunable laser sources as semiconductor and F-center lasers. They may also be installed in high f-number IR image converters.     

Proton conduction in (NH4)3 H(SO4)2 single crystals

D.C. electrical conductivity, DTA and coulometric studies on (NH₄)₃ H(SO₄)₂ single crystals are made. Conductivity is markedly anisotropic with maximum along c¹ direction. A sudden jump in the conductivity plot along c¹ direction at 413 K is supported by a large endothermic peak in DTA, confirming the presence of transition at this temperature. The values of activation energy calculated from conductivity measurements indicated that the charge carriers are protons. This was further confirmed by coulometric experiment where the gas evolved was hydrogen, as established by a gas chromatograph and the volume of H₂ released agreed with that expected from electrolysis. The mechanism of protonic conduction in this crystal is discussed.     

银催化合成Tb(BO2)3纳米棒

采用固相反应银作催化剂成功合成出棒状结构的稀土硼酸盐Tb(BO₂)₃发光材料. 利用X射线衍射和区域电子衍射研究了产物的结构特性,在700 oC煅烧时,Tb(BO₂)₃纳米棒具有良好晶形. 透射电镜分析表明,Tb(BO₂)₃纳米棒直径为100～200 nm,厚度为30～50 nm,长约3 μm. 基于Ag纳米颗粒附在Tb(BO₂)₃纳米棒的顶端和中部的事实,探讨了Tb(BO₂)₃纳米棒的生长机理. 荧光光谱研究表明,在369 nm紫外光激发下,Tb(BO₂)₃能发出Tb³⁺的特征绿色荧光,发射主峰位于546 nm,归属于⁵D₄→⁷F₅跃迁. 同时,也探讨了煅烧温度对产物的结构、形貌以及发光性质的影响.     

Growth and spectroscopic properties of Yb-doped Li6Y(BO3)3 single crystal

The spectroscopic properties of high-quality Czochralski grown 20% Yb³⁺-doped Li₆Y(BO₃)₃ single crystal as new promising laser material are presented. The crystal was seeded-grown in the 〈0 1 0〉 direction and its crystallinity was measured using X-ray rocking curve analysis. Low temperature transmission spectrum exhibits broad bands in a short range of wavelengths and two sharp lines at 972.5 and 978 nm, interpreted as two zero-lines of two nonequivalent Yb³⁺ centers inside the lattice. The fluorescence lifetimes associated to these two intense lines are different: 0.867 and 1.33 ms. An attempt of determination of the Stark sublevels energies of the ⁴F_5/2 and ⁴F_7/2 manifolds of the two Yb³⁺ nonequivalent ions is given. The polarized absorption and emission spectra were also recorded at room temperature and we conclude that the most favorable emission line for laser application could be around 1042 nm in n_g polarization.