Controllable synthesis of tetragonal LiScF4:Yb3+, Er3+ nanocrystals and its upconversion photoluminescence properties: Lithium scandium fluoride nanocrystals

Tetragonal rare-earth ions codoped LiScF₄ nanocrystals have been synthesized by a modified solvothermal method. The results revealed that the phase and morphology can be tailored through varying the synthesis conditions, such as reaction temperature and time. Meanwhile, the UC fluorescence emission spectra were measured. It turned out that the UC emission intensity can be significantly influenced by reaction temperature and time. Different from the NaYF₄:20%Yb³⁺,2%Er³⁺ nanocrystals that usually emit green emission, yellow color emission can be observed in the LiScF₄:20%Yb³⁺,2%Er³⁺ samples under 980 nm excitation, which illustrates that the obtained new phase LiScF₄ is suitable as a promising host for efficient UC fluorescence generation and tunable UC emission spectra. Moreover, the UC mechanism was investigated in detail.     

Waveguide lasers based on dielectric materials

Fifty years since the invention of the laser have been witness of the development of many different laser systems and designs. Among them, miniaturized versions of solid sate lasers based on rare-earth-doped dielectric materials have been proposed and demonstrated during the last 20 years. They are based on confined radiation provided by optical waveguide structures. Although many materials and techniques have been studied for producing planar and channel waveguides, only a few of them have shown to be adequate routes for fabricating waveguide lasers. Here we summarize the theory and specific technologies developed for characterizing waveguide structures, and we present some common fabrication techniques already successfully applied to fabricate dielectric waveguide lasers, where relevant examples of demonstrated working devices are outlined.     

Up-conversion luminescence and optical temperature sensing behaviour of Yb3+/Er3+ codoped CaWO4 material

Present article report on structural and optical properties of Er³⁺/Yb³⁺ codoped CaWO₄ phosphors. Structural properties are explored using XRD and Raman technologies. The upconversion emission has been investigated with 980 nm excitation. The upconversion emission intensity is dependent on the concentrations of Yb³⁺ ions and reaches a maximum at 7%. Logarithmic plots of power dependencies reveal that the green and red emissions originate from a two-photon upconversion process. Based on the photon energy and the emission spectra, the possible upconversion processes and emission mechanisms are discussed. Finally, the optical temperature sensing properties has been performed using the fluorescence intensity ratio technique based on green upconversion emissions. Its temperature sensitivity is found to be above 0.0025 K^-1 in the whole temperature range of 300–540 K, revealing this phosphor to be a promising optical temperature sensing material.     

Optimal performance of NdAl3(BO3)4 nanocrystals random lasers

Resonant pumping associated with the influence of the quantum-defect between the excitation and the emitted laser photons allow optimal performance of neodymium ions (Nd³⁺) based random lasers (RLs), as demonstrated here for the first time. The RL emission at 1063.5 nm due to the Nd³⁺ transition ⁴F_3/2 → ⁴I_11/2 in a powder consisting of NdAl₃(BO₃)₄ nanocrystals, was investigated by exciting the powder at 690 nm, 750 nm, 810 nm, and 884 nm in resonance with the Nd³⁺ transitions from the ground state (⁴I_9/2) to the ⁴F_9/2, {⁴F_7/2,⁴S_3/2}, {⁴F_5/2,⁴H_9/2}, and ⁴F_3/2 states, respectively. Although the Nd³⁺ absorption cross-section at 884 nm is smaller than those centered at 810 and 750 nm, excitation at 884 nm, that is in resonance with the emitting level, provided the smaller excitation pulse energy threshold and the larger slope efficiency due to the lower quantum defect.     

Effects of aging time on phase,morphology, and luminescence by two-photon processes of BiPO4:Er3+, Yb3+ in the solvothermal synthesis

BiPO₄:Er³⁺, Yb³⁺ phosphors were synthesized by the solvothermal process. The phase transformation, morphology, and UC luminescent property were characterized by different analytical techniques. The aging time has obvious influence on the phase, morphology, and luminescence of the samples. With the extension of aging time, the phase of BiPO₄:Er³⁺, Yb³⁺ phosphors changes from hexagon to monocline. The morphology changes from nanorods through nanorugbies to microoctahedra. Under the excitation at 980 nm, BiPO₄:Er³⁺, Yb³⁺ phosphors show green and red UC emissions, which originate from the (²H_11/2, ⁴S_3/2) → ⁴I_15/2 and ⁴F_9/2 → ⁴I_15/2 transitions of Er³⁺ ions. The green and red UC emission intensities increase gradually with the increase of pumping power. On the basis of the luminescent properties, one can conclude that the two-photon process is involved in green and red UC emissions.     

Energy transfer in crystalline Er,Yb:Sc2O3

The use of Yb³⁺ as a sensitizer for Er³⁺ doped laser materials is a common technique because of the high Yb³⁺ absorption cross sections. Energy transfer processes from Yb³⁺ to Er³⁺ in Sc₂O₃ are studied by two different methods. Transfer parameters describing the interactions between Er³⁺ and Yb³⁺ ions are obtained on the one hand from the ratio of emitted photons around 1.55 μm by Er³⁺ ions and around 1 μm by Yb³⁺ ions at cw excitation of Yb³⁺, on the other hand by lifetime measurements of Yb³⁺ ions in the codoped samples. Laser experiments are performed to study the suitability of Er³⁺,Yb³⁺:Sc₂O₃ as a laser material. Comparisons with energy transfer in Er³⁺,Yb³⁺:glass are made.     

Li doping effects on the upconversion luminescence of Yb3+/Er3+-doped ABO4 (A = Ca,Sr; B = W,Mo) phosphors

ABO₄ (A = Ca, Sr; B = W, Mo):Er³⁺/Yb³⁺/Li⁺ phosphors tri-doped with different concentrations of Li⁺ ion ranging from 0 to 22.5 mol% were prepared by using a solid-state reaction method. And their upconversion (UC) luminescence properties were in estimated under a 975 nm laser-diode excitation. The four kinds of phosphors (CaWO₄, CaMoO₄, SrWO₄, and SrMoO₄) tri-doped with Er³⁺, Yb³⁺ and Li⁺ ions showed strong green UC emission peaks at 530 nm and 550 nm and weak red UC emission. The intensity of green UC emission of Li⁺ doped samples was several higher than that of Li⁺ un-doped samples due to the reduction of lattice constant and the local crystal field distortion around rare-earth ions. The optimum doping concentration of Li⁺ ions was investigated and the effects of Li⁺ concentration for UC emission intensity were studied in detail.     

Optical and EPR spectroscopy of Zn:Cr:ZnSe and Zn:Fe:ZnSe crystals

Optical and EPR characterization of Cr and Fe doped ZnSe crystals annealed in Zn vapor revealed a strong bleaching of the divalent state of transition metal ions. Photo induced EPR kinetics were studied in 20–80 K temperature range. Analysis of time-dependent data reveals Cr¹⁺ signal rise time decreases with increasing temperature. The non-exponential decay of Cr¹⁺ concentration were analyzed using Auger-type recombination process. The photoluminescence quantum yield of Cr²⁺ ions at ⁵E(D) → ⁵T₂(D) mid-IR transition excited via chromium ionization process was measured to be close to 100%.     

Ultrafast lasers: A new frontier for optical materials processing

In the last years, ultrashort laser pulses have gone through the laboratory walls to burst into the industrial arena as a tool for material micro- and nanoprocessing. The number of industrial fields and specific applications is steadily growing, reaching the nanotechnology applications. Now, we celebrate the 25th anniversary of the CPA (chirped pulse amplification) technique which made available intense ultrashort (subpicosecond) pulses able to induce ablation of any material. This contribution tries to review the fundamentals of ultrafast lasers as well as some of their applications, emphasizing the processing of optical materials.     

Synthesis of LaF3: Yb3+ ,Ln3+ nanoparticles with improved upconversion luminescence

Yb³⁺/Er³⁺ and Yb³⁺/Tm³⁺ co-doped LaF₃ nanoparticles with upconversion luminescence properties were prepared via the co-precipitation method, followed by heat treatment at different temperatures in the range of 180°C to 600°C. We investigated the influence of heat treatment temperatures on the size, morphology, and upconversion luminescence intensity of the nanoparticles. Significant increases of the particle size and upconversion luminescence intensity of the nanoparticles were observed with increasing heat treatment temperature. The upconversion mechanism of the LaF₃:Yb³⁺,Er³⁺ and LaF₃:Yb³⁺,Tm³⁺ nanoparticles was also discussed.     

NaYF4:Er3+和NaYF4:Yb3+/Er3+上转换荧光纳米晶的制备与表征

以EDTA为螯合剂,采用络合共沉淀法合成了NaYF4:Er3+和NaYF4:Yb3+/Er3+纳米晶.分别采用XRD、SEM、荧光分光光度计对合成的样品进行了结构、形貌和上转换荧光分析.XRD结果表明,制备的NaYF4:Er3+和NaYF4:Yb3+/Er3+均为纯立方相;SEM结果显示,制备的NaYF4:Er3+和NaYF4: Yb3+/Er3+晶粒粒径都在100nm左右,与NaYF4:Er3+相比,NaYF4:Yb3+/Er3+晶粒尺寸分布更均匀,分散性更好,符合作为荧光标记材料的要求;上转换荧光分析表明,在980nm激光器激发下,NaYF4:Yb3+/Er3+的发光强度比NaYF4:Er3+提高了1个数量级.     

Simulation of Tm 3+ -doped silica and Er 3+ -doped fluorozirconate fibre lasers

Computer simulation of the operation of diode-pumped Tm³⁺-doped silica and Er³⁺-doped fluorozirconate fibre lasers that use cladding-pumping models high-power continuous-wave output at wavelengths near 2 and 3 μm. The model has been used to examine the fibre laser performance for a variety of fibre and pump configurations. Good agreement has been found between the model calculations and published experimental measurements. The model has determined the slope effciency and relative performance of the fibre lasers when the pump wavelength was varied over the ³F₄ and ³H₄ absorption bands of Tm³⁺ and the ⁴⁺I_11/2 absorption band of Er³⁺. The calculated maximum slope effciencies were determined to be about 40, about 71 and about 31% respectively, for each absorption band pump scheme. The model was further used to analyse the fibre laser output when the Tm 3+ and Er 3+ dopant concentrations, absorption conditions and diffraction conditions are varied and the consequences on the operation of the fibre laser with these variations are discussed.     

Polarized spectral properties of Sm3+:LiLuF4 crystal for visible laser application

A Sm³⁺-doped LiLuF₄ single crystal was grown by the vertical Bridgman–Stockbarge technique. Polarized absorption spectra, polarized fluorescence spectra, and fluorescence lifetime of the Sm³⁺:LiLuF₄ crystal were recorded at room temperature. Based on the Judd–Ofelt theory, spectral parameters of the Sm³⁺:LiLuF₄ crystal were calculated. Emission cross sections for the ⁴G_5/2 → ⁶H_J (J = 5/2, 7/2, 9/2, and 11/2) transitions with special interest for visible laser application were obtained by the Füchtbauer–Ladenburg formula. The results indicate that the Sm³⁺:LiLuF₄ crystal may be a potential laser gain medium operating in visible region pumped by diode lasers around 401 nm.     

Thermal analysis of a diffusion bonded Er3+,Yb3+:glass/Co2+: MgAl2O4 microchip lasers

The analysis of thermal effects in a diffusion bonded Er³⁺,Yb³⁺:glass/Co²⁺:MgAl₂O₄ microchip laser is presented. The analysis is performed for both wavelengths at 940 nm and at 975 nm as well as for two different sides of pumping, glass side and saturable absorber side. The heat sink effect of Co²⁺:MgAl₂O₄, as well as the impact of the thermal expansion and induced stress on the diffusion bonding are emphasised. The best configurations for reducing the temperature peaks, the Von Mises stresses on the diffusion bonding, and the thermal lensing are determined.     

Polyol-mediated synthesis of water-soluble LaF3:Yb,Er upconversion fluorescent nanocrystals

Well-crystallized LaF₃:Yb,Er nanoparticles were prepared by the polyol method and three kinds of polyols (glycol, diethylene glycol and glycerol) were chosen as the reaction medium respectively. All of the obtained LaF₃:Yb,Er nanoparticles have roughly spherical shapes, and the average sizes of these nanoparticles ranged from 5 to 7 nm. These nanoparticles could be well dispersed in water or ethanol to form colloidal solutions. When these nanoparticles were excited by the 980 nm laser, several upconversion emissions were observed.     

Ce^3+/Yb^3+共掺LiLuF4单晶的紫外和近红外发光研究

采用改进的坩埚下降法成功生长了Ce^3+/Yb^3+离子双掺杂LiLuF4单晶, Ce^3+的初始离子掺杂浓度为0.1mol%,Yb^3+离子浓度从0变化到2.0mol%。在波长291 nm激发时观察到Yb^3+在1020 nm(2F5/2→2F7/2)附近的强近红外发射以及Ce^3+在300~350 nm(5d→4f)的紫外发射。通过吸收光谱、荧光光谱研究了Yb^3+离子掺杂浓度对Ce^3+/Yb^3+共掺杂LiLuF4单晶光谱性质的影响及Ce^3+到Yb^3+离子的能量转移机理。通过变温光谱的研究发现,当环境温度从298 K增加到443K时,其荧光发射强度不断降低。Ce^3+/Yb^3+共掺杂LiLuF4单晶发光波长主要位于紫外和近红外,这种独特的发光属性可望用于防伪技术和公共安全事务中。     

Comparison of laser generation in thermally bonded and unbonded Er3+,Yb3+:glass/Co2+:MgAl2O4 microchip lasers

Pulse laser generation in several Er³⁺,Yb³⁺:glasses thermally bonded with Co²⁺:MgAl₂O₄ was achieved. Peak power in the range of 1.83–7.68 kW with pulse duration between 2.9 and 4.2 ns and energy up to 24 μJ was obtained. The output characteristics for different transmissions of the output couplers were investigated. To show the improvements gained by the thermal bonding procedure, a comparison of thermally bonded and unbonded samples was done in terms of generation efficiency, peak power, beam quality, generated spectra and pulse to pulse jitter.     

Luminescent properties of EuGa2S4:Er3+

We have studied the thermo-and photoluminescence of undoped and Er³⁺-doped EuGa₂S₄ crystals in the temperature range 77–450 K. In thermoluminescence studies, different heating rates and excitation intensities have been used. The results demonstrate that, with increasing heating rate, the intensity of thermoluminescence peaks grows, and the peaks shift to higher temperatures. EuGa₂S₄:Er³⁺ crystals exhibit both Stokes and anti-Stokes luminescence. The mechanisms of these processes are analyzed.     

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.