Spectroscopic properties and high-power laser operation of Yb0.14:Y0.77Gd0.09Ca4O(BO3)3 mixed crystal

We report, for the first time to our knowledge, on the spectroscopic properties and continuous-wave laser performance of Yb_0.14:Y_0.77Gd_0.09Ca₄O(BO₃)₃, a mixed rare earth calcium oxyborate Yb-ion crystal. Under simple end-pumping conditions with a 976-nm diode, efficient CW laser operation was demonstrated at room temperature, producing an output power of 14.1 W at 1084.4 nm with an optical-to-optical efficiency of 48%; while operating around 1045 nm, the laser could generate an output power as high as 23.0 W, with optical-to-optical and slope efficiencies amounting, respectively, to 57% and 70% with respect to incident pump power. The polarized absorption and emission cross sections are also presented. The impressive results demonstrated reveal the great potential of these mixed oxyborates in developing new promising Yb-ion laser crystals.     

Spectroscopic properties of HoAl3(BO3)4 single crystal

The Judd–Ofelt theory has been applied to analyze absorption spectra of Ho³⁺ ion in HoAl₃(BO₃)₄ measured in spectral range 300–700 nm at room temperature. The Judd–Ofelt spectroscopic parameters have been determined as: Ω₂ = 18.87 × 10⁻²⁰ cm², Ω₄ = 17.04 × 10⁻²⁰ cm², Ω₆ = 9.21 × 10⁻²⁰ cm². These parameters have been used to calculate radiative lifetimes and branching ratios of the luminescence manifolds. Three luminescent bands were found in the spectral range 450–700 nm ascribed to transitions from the ⁵F₅, (⁵F₄, ⁵S₂) and ³K₈ states to the ground state ⁵I₈. Experimental intensities of these luminescence transitions were compared with those calculated by using Judd–Ofelt theory and the system of kinetic equations for populations of starting luminescing states. Probabilities of radiativeless transitions were evaluated from this comparison.     

Nd3+:Y0.5Gd0.5VO4晶体生长和基本特性

Nd^3 :Y0.5Gd0.5VO4晶体作为一种新的激光材料，可以用中频感应加热提拉法生长。X射线粉末衍射分析表明它的结构与Nd^3 :YVO4晶体结构相同，它的晶格常数介于YVO4和NdVO4晶格常数之间。用ICP光谱法测定晶体中Nd^3 含量为0．8at％，分凝系数为0．8，与Nd^3 :GdVO4晶体中Nd^3 的分凝系数0．78相当；用称重法测定其密度为5．00g／cm^3；用稳态纵向热流法测出其室温热导率为12．5W／mK。实验表明Nd^3 :Y0.5Gd0.5VO4晶体有希望作为高功率ID泵浦激光晶体材料。     

Optical transition probability of Nd3+ ion in α-Ba3Y(BO3)3 crystal

Optical absorption and emission intensities have been investigated for the Nd³⁺ ion in α-Ba₃Y(BO₃)₃ crystal. Based on the Judd-Ofelt theory the spectral parameters were obtained. The intensity parameters Ω_λ are: Ω₂ = 0.62 × 10^–20 cm², Ω₄ = 0.90 × 10^–20 cm², Ω₆ = 1.06 × 10^–20 cm². The radiative lifetime is 1104 μs, and quantum efficiency is equal to 6.9%. The fluorescence branching ratios are: β₁ (0.88 μm) = 0.4050, β₂ (1.06 μm) = 0.4897, β₃ (1.35 μm) = 0.1000 and β₄ (1.88 μm) = 0.0053. Electronic Publication     

PDP用高亮度(Y,Gd)BO_3:Tb~(3+)绿色荧光粉的合成

采用共沉淀法制备了稀土氧化物前体,再将其和H3BO3及BaB4O7混合后,用高温固相合成法制备出了2.0-3.0μm粒径的(Y,Gd)BO3:Tb3+绿色荧光粉。研究发现,荧光粉的粒度随前驱体粒度与助熔剂引入量的增加而增大,助熔剂的引入量超过0.18%会使荧光粉的亮度猝灭;随着灼烧温度的增高,荧光粉的亮度会变大。综合PDP用荧光粉的使用特性,BaB4O7的引入量在0.10%,灼烧温度为1100℃时,采用共沉淀法前驱体可得到亮度104,粒度2.5um,晶型完美的(Y,Gd)BO3:Tb3+绿色荧光粉。     

Temperature phase-matching properties for harmonic generation in GdCa4O(BO3)3 and Gd(x)Y(1-x)Ca4O(BO3)3

GdCa4O(BO3)3 has been found to have phase-matching points where the temperature variations of the phase-matching angles become zero for type-1 sum-frequency generation in the zx plane. We also found that the temperature sensitivities of the phase-matching conditions in the zx plane are different along the phi = 0 degrees and phi = 180 degrees directions in this material. In addition, the thermo-optic dispersion formula of this material that reproduces the temperature phase-matching properties of GdCa4O(BO3)3 and Gd(x)Y(1-x)Ca4O(BO3)3 is presented.     

Highly Nd3+-doped Y3Al5O12 crystal fiber tip for laser thermotherapy

Based on phonon relaxation, a 12-at. % neodymium-doped YAG (Y3AlrO12) crystal fiber tip has been developed for photothermal conversion. The near-cylindrical tip, with an average diameter of 0.68 mm and a length of 1.8 mm, is fabricated on a 0.65-mm-thick 220-mm-long pure YAG single-crystal fiber by laser-heated growth. Pumped by an 810-nm wavelength diode laser with a pump power of less than 2 W, the temperatures of the tip reach 725 degrees C in air, 78 degrees C in egg white, and 79 degrees C in porcine liver, with acceptable reproducibilities and thermal response times. The photothermal conversion efficiency of the doped tip is approximately 89%, and the high stability of the tip is also proved. Experimental results show that the doped fiber tip is promising for laser thermotherapy applications.     

自变频激光晶体Nd3+:GdAl3(BO3)4的研究

采用熔盐法生长出尺寸为30mm的Nd3+:GdAl3(BO3)4优质晶体,进行了吸收光谱和荧光光谱的测定研究,计算得到晶体发射截面为σ1061.9e=2.9×10-19cm2和σ1338nme=5.5×10-20cm2.采用染料激光器作为泵浦源,对晶体进行了自变频激光实验研究,在紫外可调谐(378～382nm)、绿光531nm、蓝光(436～443nm)、红光(669nm)和红外可调谐(1305～1365nm)波段实现了激光输出,输出的最大功率分别为:105μJ/脉冲、119.5μJ/脉冲、445μJ/脉冲、19μJ/脉冲和31μJ/脉冲.     

Changes of the local magnetic properties of the optically excited Nd3+ ions and their manifestation in the near IR spectra of the Nd0.5Gd0.5Fe3(BO3)4 crystal

Polarized absorption spectra of f–f transitions ⁴I_9/2 → ⁴F_3/2 and (²H_9/2 + ⁴F_5/2) in the Nd³⁺ ion in the Nd_0.5Gd_0.5Fe₃(BO₃)₄ single crystal were studied as a function of temperature in the range of 2–40 K and as a function of magnetic field in the range of 0–65 kOe at 2 K. It was found out that the selection rules for f–f electron transitions substantially changed in the magnetically ordered state of the crystal, and they strongly depended on the orientation of the Fe and Nd ions magnetic moments relative to the light polarization. The splitting of the ground and excited states of the Nd³⁺ ion in the exchange field of the Fe sublattice were determined. It was revealed that the value of the exchange splitting (the exchange interaction) in the excited states did not correlate with the theoretical Landé factors. The Landé factors of the excited states were experimentally found. In general, the local magnetic properties in the vicinity of the excited ion depend substantially on its electron state. In particular: (1) in one of the excited states a weak ferromagnetic moment appears, (2) the changes of type of the local magnetic anisotropy take place in some excited states, and (3) in some excited states the energetically favorable orientation of the Nd³⁺ ion magnetic moment is opposite to that in the ground state. In some excited states the nonequivalent Nd³⁺ centers were found out.     

1.06 μm laser characteristics of γ-Nd3+:LaSc3(BO3)4 crystal

This paper reports the pulse laser characteristics of the new polymorph γ-Nd³⁺:LaSc₃(BO₃)₄ (γ-NLSB) crystal. The maximum laser output of a γ-NLSB rod with dimensions of Φ3.3 mm×15 mm was 83.0 mJ at 1.06 μm, pumped by a single Xenon flash-lamp of Φ3.0 mm×20 mm. The overall and average slope efficiencies were 0.78% and 1.02%, respectively. The laser energy threshold value E_th was lower than 0.2 J, and the extinction ratio of the crystal was 39.38 dB, the output laser of 1.06 μm was the linear polarized light. Electronic Publication     

Synthesis and luminescent properties of (Y,Gd)BO3:Eu coated with MgF2

(Y,Gd)BO₃:Eu powders were prepared by conventional solid-reaction method. Surface-modified (Y,Gd)BO₃:Eu powders with MgF₂ were prepared by the emulsion method. The best preparing way is that MgCl₂ was dropped to the mixture of NH₄F and (Y,Gd)BO₃:Eu powders to prepare surface-modified (Y,Gd)BO₃:Eu powders. The interaction between F⁻ ions and the phosphor particles was discussed. It is shown that the structures of surface-modified (Y,Gd)BO₃:Eu powders were measured by XRD. The luminescent properties of (Y,Gd)BO₃:Eu powders with MgF₂ are researched.     

Efficient laser operation at 1.06 μm in co-doped Lu3+, Nd3+:GdCa4O(BO3)3 single crystal

Efficient laser emission at 1.06 μm was obtained from a diode-laser quasi-continuous wave pumped Nd_0.04Gd_0.86Lu_0.10Ca₄O(BO₃)₃ (Nd:GdLuCOB) single crystal. An uncoated, 6.0-mm long, ZX-cut Nd:GdLuCOB medium yielded laser pulses with 1.76 W peak power for absorbed pump pulses of 5.49 W peak power, corresponding to an overall optical-to-optical efficiency η_oa = 0.32; the slope efficiency was η_sa = 0.44. Comparison is made with an uncoated XY-cut Nd:GdCOB medium (4.0-at.% Nd doping and 6.8-mm length) from which laser pulses with 1.74 W peak power (at optical efficiency η_oa = 0.25) and 0.31 slope efficiency were obtained. The improvements in laser emission of Nd:GdLuCOB at the fundamental wavelength are important for future self-frequency doubling in ZX principal plane of this crystal.     

Anisotropy in laser performance of Yb:GdCa4O(BO3)3 crystal

We report distinct laser performance of Yb:GdCa(4)O(BO(3))(3) crystals cut along different principal optical axes using an unpolarized diode pump. The continuous-wave (cw) laser oscillation generated with y-cut crystal is polarized either with E parallel x or with E parallel z depending on the output coupling (T) utilized; a specific T=3% leads to a special situation in which the two orthogonal polarization states coexist oscillating at different wavelengths. The laser oscillation achieved with x- and z-cut crystals is also polarized, but with a fixed polarization of E parallel z and E parallel x, respectively. The most efficient laser operation is obtained with the y-cut crystal, generating a cw output power of 7.35 W at 1083-1085 nm with an optical-to-optical efficiency of 63%, the slope efficiency being as high as 84%.     

Spectroscopic properties of Er3+ ions in La2(WO4)3 crystal

Er³⁺-doped La₂(WO₄)₃ single crystals were grown by the Czochralski technique. The absorption spectra, fluorescence spectra and fluorescence decay curves of the crystals were measured at room temperature. The spectroscopic parameters, including intensity parameters Ω_t (t = 2, 4, 6), spontaneous emission probability, fluorescence branching ratio, radiative lifetime, and stimulated emission cross-section were estimated. The fluorescence decay curves of fluorescence manifolds ⁴I_13/2, ⁴I_11/2, and ⁴S_3/2 were measured for crystal and powder samples, respectively. The effect of radiation trapping on the spectroscopic parameters was discussed. Green up-conversion fluorescence bands centered at wavelengths of 530 nm and 550 nm were observed when the crystal was excited at 977 nm. The possible up-conversion mechanisms were proposed.     

Synthesis and photoluminescence properties of (Y,Gd)BO3 : Eu phosphor prepared by ultrasonic spray

The mixed solution of acetate of Y, Gd, Eu and boric acid diluted in water was used as the precursor for the ultrasonic spray for the synthesis of (Y,Gd)BO₃ : Eu phosphor. It was found that (Y,Gd)BO₃ : Eu phosphor made by ultrasonic spray pyrolysis had a spherical shape and a narrow size distribution having a mean size of 1.3 m, while it had irregular, coarse and non-uniform size distribution for the phosphor formed by solid-state reaction. The as-sprayed particles was amorphous but they converted into the same polycrystalline phase of solid state reaction after post heat treatment at 1100 °C for 2 hr. The emitting intensity under 147 nm VUV excitations for the spray-formed (Y,Gd)BO₃ : Eu phosphor, however, was inferior to the later one. It was found that the optimum concentrations of Gd and Eu were 30% and 5%, respectively in (Y_1–x Gd _x )_1–y BO₃ : Eu _y phosphors prepared both by spray and solid state reaction.     

Luminescent properties of YAl3(BO3)4:Eu3+ phosphors

YAL₃(BO₃)₄:Eu³⁺ phosphors were fabricated by the sol-gel method. The structure properties were measured by x-ray diffraction (XRD) and infrared spectra (IR). Doping concentration of Eu³⁺ ions in YAL₃(BO₃)₄:Eu³⁺ phosphors of 0, 1, 3, 4, and 5 mol% were studied. The excitation spectra and emission spectra of YAL₃(BO₃)₄:Eu³⁺ phosphors were examined by fluorescent divide spectroscopy (FDS). The luminescent properties of YAL₃(BO₃)₄:Eu³⁺ phosphors are discussion. The optimal doping concentration of Eu³⁺ ions in YAL₃(BO₃)₄:Eu³⁺ phosphors was found to be approximately 3 mol%.     

Monolithic wavelength converter for ultraviolet light by use of a Gd(x)Y(1-x)Ca4O(BO3)3 crystal

Gd(x)Y(1-x)Ca4O(BO3)3 (GdYCOB) is a promising nonlinear optical crystal that shows high effective nonlinearity d(eff), noncritical phase matching, and high chemical stability. We report on the fabrication and characteristics of a monolithic wavelength converter, which generates ultraviolet light by the incidence of a 1.064 microm near-infrared laser. The converter consists of GdYCOB for third-harmonic generation, KTiOPO4 (KTP) for second-harmonic generation, and a wave plate. GdYCOB has the advantage of an extremely wide angular acceptance bandwidth, whereas KTP exhibits a high effective nonlinear coefficient and a broad temperature bandwidth. Consequently the combination of these crystals results in highly efficient and stable ultraviolet conversion for constructing a compact and robust ultraviolet laser.     

Tuning of crystal phase and luminescence properties of Gd2(MoO4)3:Dy3+ phosphors

The orthorhombic and monoclinic Gd₂(MoO₄)₃:Dy³⁺ were successfully synthesized by a hydrothermal process with a subsequent annealing treatment at 800 °C for 4 h. The crystal phase of Gd₂(MoO₄)₃:Dy³⁺ was controlled as a function of the pH value of the solution. The crystallization and microstructures of the samples were characterized by Powder X-ray diffraction (XRD) and scanning electron micrograph (SEM). Furthermore, the optical properties were investigated by the diffuse reflection, excitation and emission spectra. The mechanisms of different crystal phases affected on the luminescence properties of Gd₂(MoO₄)₃:Dy³⁺ were discussed. The electric dipole–dipole interaction between Dy³⁺ ions was identified as the main mechanism for the concentration quenching of the two structures. Finally, the chromatic natures of all the samples were analyzed in detail. The results indicate that the orthorhombic phosphor Gd_1.84(MoO₄)₃:Dy_0.16³⁺ can be considered as a suitable candidate for white light emitting diodes (W-LEDs).