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A series of Dy3+-activated CaYAl3O7 (Dy: CaYAl3O7) phosphors were synthesized by the solid-state reaction at high temperature. The prepared phosphors were characterized by X-ray diffraction, and the results showed that the main phase of the phosphor was CaYAl3O7. The structure of CaYAl3O7 was investigated and the first-principles calculations were carried out for the first time. The photoluminescence properties of them were investigated in detail through the measurements of their emission spectra and fluorescence decay curves. The fluorescence decay curves of the 4F9/2 state with different Dy3+ ions concentrations exhibited multi-exponential decaying behavior, then the lifetimes were fitted and compared. Furthermore, the energy transfer processes within Dy: CaYAl3O7 phosphors were investigated. In the visible region, a strong emission band was observed with peak at 574 nm, corresponding to 4F9/2 → 6H13/2 transition, which indicates that Dy: CaYAl3O7 is good material for yellow light applications.

A new rare-earth borate Er6B4O15was synthesized by a solid-state reaction technique. The crystal was obtained by a flux method. Single-crystal X-ray diffraction analysis revealed that the crystal structure is composed of ErO6polyhedra sharing edges and BO3groups. The absorption, near-infrared fluorescence spectra and the fluorescence decay curve of Er:4I13/2energy level in the Er6B4O15crystal were measured at room temperature. The absorption peak was located at 977 nm with absorption cross section of 1.16 × 10−21 cm2and a full width at half-maximum (FWHM) of 16 nm, which is very suitable for commercial 980 nm laser diode pumping. A maximum emission peak at 1560 mm with a broad FWHM of 64 nm was observed in this crystal because of the Er3+transition4I13/2→4I15/2, while the emission cross section was calculated to be 8.53 × 10−20 cm2. These results imply that the Er6B4O15crystal is a promising candidate material for the achievement of an eye-safe near-infrared wavelength laser.

Single crystals of pure and Er 3+ doped CaLaGa 3 O 7 were firstly grown by the Czochralski technology. The structure of CaLaGa 3 O 7 was investigated. The electronic structures of CaLaGa 3 O 7 crystal were performed by using first-principles calculations based on density functional theory (DFT) methods. Its band structure and density of states were presented. The polarized absorption, emission spectra including up-conversion, near-infrared and mid-infrared fluorescence spectra, as well as the fluorescence decay curves of Er: CaLaGa 3 O 7 crystal were measured at room temperature. Detailed spectroscopic analyses of Er: CaLaGa 3 O 7 were carried out. Based on the Judd–Ofelt theory and the polarized absorption spectra, the spontaneous transition probabilities, the fluorescent branching ratios and the radiative lifetimes were calculated. The energy transfer mechanism in Er: CaLaGa 3 O 7 crystal was also studied in this work. It concludes that Er: CaLaGa 3 O 7 crystal can act as a promising candidate for mid-infrared lasers.

1 at% Dy3+: CaF2 and 1 at% Dy3+/5 at% Y3+: CaF2 crystals were grown by Bridgman method. Absorptions, visible and mid-infrared emissions, and fluorescence decay curves were measured. By applying Judd-Ofelt (J-O) theory, for Dy3+/Y3+: CaF2 crystal stronger oscillator strength and radiation transition probability were derived. The effect of Y3+ ions incorporation into CaF2 crystals on the light emission of Dy3+ ions was discussed. Co-doped Y3+ ions can destroy Dy clusters, cripple the concentration quenching effect, and enhance the yellow and mid-infrared fluorescence intensity. The yellow fluorescence intensity of Dy3+/Y3+: CaF2 is ~ 70 times higher than that of Dy3+: CaF2 crystal. The local structure of Dy3+ ions was analyzed, and co-doping Y3+ can increase the quantity of tetragonal Dy clusters. In Dy3+/Y3+: CaF2 crystal, the tetragonal Dy clusters occupy the dominant position, and the fluorescence lifetime (τf) is relatively short. It can be concluded that Dy3+: CaF2 and Dy3+/Y3+: CaF2 crystals are expected to achieve yellow and mid-infrared laser output simultaneously.

Mid-infrared waveband lasers have demonstrated important applications in the fields of atmosphere pollution monitoring, gas flow monitoring, ocean detection, laser medicine, military confrontation and basic scientific researches etc. In this paper, we review the research development of bulk crystal growth, physicochemical, spectral and laser properties of 2.5–5.0 μm waveband mid-infrared laser crystals in recent years. A serial of gallate and aluminate crystals with low phonon energy were grown by the Czochralski method, such as Er3+ activated and rare earth ions co-doped Gd3Ga5O12(GGG), SrGdGa3O7, SrLaGa3O7, CaYAlO4 and CaGdAlO4 crystals, Ho3+ activated and rare earth ions co-doped GGG crystals, as well as Dy3+:YAlO3 crystals, and 2.5–3.4 μm waveband emissions were obtained in these crystals. High quality Dy3+:KPb2Cl5, Cr2+:CdSe and Cr2+:Fe2+:CdSe crystals were grown by the Bridgman method, and 2.5–5.0 μm waveband emissions were obtained in these crystals. The physicochemical and spectral properties of the above crystals were studied systematically, with focus on analyses of the concentration effect of activated ions Er3+, the sensitization mechanism of the co-dopant sensitized ions and the impact of the depopulated ions on the inhibition of self-termination effect. The fluorescence dynamic of the activated ions within the mid-infrared waveband, the energy transfer efficiencies between activated ions and co-dopant sensitization ions, as well as between the activated ions and co-dopant depopulation ions were calculated, and the energy transfer mechanism was discussed. Based on the results of spectroscopic investigations, the concentrations of Er3+, the types and the concentrations the co-dopant sensitization ions were optimized in different kinds of crystals. The laser properties of Er3+ activated GGG, CaYAlO4 crystals were presented. Finally, 2.7–2.8 µm multi-wavelength CW or pulsed lasers were achieved in Er:GGG, Er,Pr:GGG and Er:GGG/GGG composite crystals end-pumped by 965 nm LD or in Cr,Er:YSGG crystals by Xenon lamp, furthermore, the single longitudinal mode microchip laser was achieved in Er:GGG crystal for the first time.

A new rare-earth borate Er

In order to make accurate forecast of mobile Internet diffusion trend. This paper proposes a method which is based on Bass innovation diffusion model. To solve the problem that the parameters of the model are difficult to estimate, a modified particle swarm optimization algorithm (PSO) whose inertia weight changes dynamically is introduced to search the most precise parameters. The application of the index of population density helps determine the convergence status of population. When the algorithm is trapped into local optimum, the combination of Cauchy mutation and Gaussian mutation is applied on the global best particle. The results of the experiment show that optimized Bass model is suitable for predicting mobile Internet diffusion trend and the proposed algorithm can effectively improve the precision of the optimal solution as compared to existed estimation methods.

We report ∼2.8 μm emission of Er3+-doped Lu3Ga5O12 crystal, as well as its laser performance. The continuous-wave (CW) and passively Q-switched lasers were both obtained for the first time at room temperature under 967 nm laser diode end pumping. A 384 mW of CW output power was obtained under the absorbed pump power of 3.28 W, corresponding to an optical-to-optical efficiency of 11.7%; the slope efficiency was 14.1%. A passively Q-switched laser with a maximum average output power of 274 mW was also achieved by utilizing a Bi2Te3/graphene heterostructure saturable absorber (SA). The shortest Q-switched pulse duration and the repetition rate were 340 ns and 135 kHz, respectively.

High concentration of 15 at.% Yb 3+ doped LaCa 4 O(BO 3 ) 3 (LaCOB) crystal was grown by Czochralski technique. The absorption cross section was conclulated to be 0.63 × 10 −20 cm 2 at 977 nm and the emission cross section to be 0.39 × 10 −20 cm 2 at 1030 nm, with the FWHM of 6.15 and 33 nm respectively. Laser potentiality was evaluated based on the gain cross section σ g , the minimum inversion fraction β min and the minimum pump intensity I min , which were calculated to be 0.18 × 10 −20 cm 2 , 0.05 and 0.47 kw/cm 2 , respectively. Continuous wave laser operation was realized with an output power of 0.77 W and a slope efficiency of 15.71%. The laser emitted around 1077 nm. The radiation trapping and continuous pump mode are contributed to the lasing wavelength for present crystal.

The optical properties and dual-polarization laser operation of Yb3+:NaY(WO4)2 doped with different concentrations of Yb3+ ions have been detailedly studied in this paper. Single crystals of NaY(WO4)2 doped with 10 at%, 15 at%, 20 at%, 30 at% and 45 at% Yb3+ have been grown by the Czochralski method respectively. By comparing their room temperature polarized absorption and emission cross sections, we found that the 10 at% Yb3+:NaY(WO4) was more appropriate for laser operation. Finally the dual-polarization and dual-wavelength laser properties of 10 at% Yb3+:NaY(WO4) were measured with the output coupler of T = 3%, Rc = 75 mm. An output of 2.33 W of was achieved, which was calculated by 1000 Hz and 0.3 duty ratio pulse, and its slope efficiency is 41.3%. An output of 1.75 W of orthogonally polarized dual-wavelength laser at 1050 nm and 1055 nm was also obtained.

Nano-Fe powders could be prepared only after 10 hours of ball milling assisted by dielectric barrier discharge (DBD), whose particle mean size was about 100 nm. The synergetic refinement mechanism of DBD on ball milling had been investigated by examining the morphology of Fe powder using scanning electron microscopy and transmission electron microscope. It was shown through SEM that Fe particles displayed an extraordinary plasticity in the early assisted milling stages under the action of DBD, and the plastic deformation of Fe particles was more severe than that in normal milling. Large quantity of Fe particles about 50 nm were observed by TEM which were generated during ball milling owing to the hot explosion effect caused by DBD electron bombardment. It was indicated that the refinement of Fe powder in DBD assisted ball milling could be promoted by the synergy effect of superplasticity, hot explosion and huge pulsating stress which were caused by the high-energy electron bombardment.

Singly doped and Tm 3+ /Ho 3+ co-doped NaY(WO 4 ) 2 single crystals were grown successfully by Czochralski method. The room temperature polarized absorption and fluorescence spectra as well as the decay curves were measured. Spectroscopic parameters related to the laser operation around 2.0 μm via the 3 F 4 → 3 H 6 (Tm 3+ ) and 5 I 7 → 5 I 8 (Ho 3+ ) transitions have been evaluated. The energy level scheme and energy transfer processes of Tm 3+ and Ho 3+ were analyzed.

A Pr3+-doped SrMoO4 single crystal has been grown successfully by the Czochralski technique. The absorption spectra, fluorescence spectra, and fluorescence decay curves have been measured at room temperature. The spectroscopic parameters, including spectroscopic parameters Ωt (t = 2,4,6), radiative transition probabilities, radiative lifetimes and branching ratios were determined according to the standard and modified Judd–Ofelt theories. The stimulated emission cross-sections, the fluorescence lifetimes and the quantum efficiency of Pr3+ ions in SrMoO4 were obtained. This study implies that Pr3+:SrMoO4 is an attractive candidate for solid-state laser medium.

The room-temperature absorption spectrum, fluorescence spectra, and fluorescence decay curves of Pr 3+ -doped Gd 3 Ga 5 O 12 single crystal were studied systematically. The standard and modified Judd–Ofelt theories were used to determine the Judd–Ofelt intensity parameters Ω t ( t = 2, 4, 6), radiative transition probabilities, radiative lifetimes and branching ratios. The stimulated emission cross-sections and the fluorescence quantum efficiency of the promising laser levels were calculated and discussed. The multi-exponential behavior of the fluorescence decay curve of the 1 D 2 → 3 H 4 transition was explained by using the Inokuti–Hirayama theory. The obtained spectroscopic results show the potential application of the Pr 3+ -doped Gd 3 Ga 5 O 12 crystal as visible solid-state lasers.

Single crystal Tm 3+ :SrMoO 4 was grown successfully by Czochralski technique along the (0 0 1) orientation in N 2 atmosphere. The refractive index of SrMoO 4 crystal was measured at room temperature. The linear thermal expansion coefficients along c - and a -axes were measured to be 1.70 × 10 −5 °C −1 and 0.59 × 10 −5 °C −1 , respectively. Its polarized absorption spectra, fluorescence spectra and fluorescence decay curve have also been investigated at room temperature. Based on the Judd–Ofelt theory, the intensity parameters have been determined as: Ω 2 = 7.875 × 10 −20 , Ω 4 = 2.797 × 10 −20 and Ω 6 = 0.92 × 10 −20 cm 2 . The radiative probabilities, radiative branching ratios, radiative lifetimes and stimulated emission cross sections of Tm 3+ in SrMoO 4 were obtained. The quantum efficiency of the 3 H 4 level is determined to be approximately 88.56% for this material.

The polarized absorption and emission spectra have been measured for the Tm3+ doped NaY(MoO4)2 crystal and spectral parameters have been estimated from the absorption data based on the Judd–Ofelt theory. The effective intensity parameters Ω t eff (t = 2, 4, 6) are 11.67 ×10−20, 2.21 × 10−20, 1.74 × 10−20 cm2, respectively. From the intensity parameters, the radiative transition probabilities, radiative lifetimes, branching ratios and the emission cross-section have been calculated. In comparison with other Tm3+ doped laser crystals, Tm3+:NaY(MoO4)2 crystal has potential as a promising laser crystal.

The single crystal of ZnWO 4 :Ho 3+ was grown by Czochralski technique. The XRD, absorption spectra, fluorescence spectrum are presented, and the Judd–Ofelt (J–O) intensity parameters Ω 2 , Ω 4 , Ω 6 are obtained to be 4.61 × 10 −20 cm 2 , 0.16 × 10 −20 cm 2 , 0.48 × 10 −20 cm 2 , respectively. Calculated radiative transition rate, branching ratios, and radiative lifetime for different transition levels of ZnWO 4 :Ho 3+ crystals are presented. The most intense line correlative with the transition 5 S 2 → 5 I 8 at 543 nm is potentially used for green solid state laser, and the fluorescence lifetime of this energy level is 14.1 μs.

NaLa(WO4)(2):Dy3+ crystals were grown successfully by the Czochraski technique. The Raman, infrared, electronic absorption and emission spectra were measured at room temperature. The Judd-Ofelt theory, extended to anisotropic system, has been applied to evaluate the intensity parameters Omega(t) (t=2, 4, 6), radiative transition rates A, radiative lifetimes tau(R), and fluorescent branching ratios. Although there are several transitions originating in the F-4(9/2) level, a major part of emission intensity is contained in the F-4(9/2) -> 6H(13/2) transition. The stimulated emission cross-sections for this transition were estimated by using the Fochtbauer-Ladenburg method. The luminescence decay curve was also measured at room temperature. The results indicate that NaLa(WO4)(2):Dy3+ may be considered as laser active materials operating near 0.57 mu m. (C) 2006 Elsevier B.V. All rights reserved.

Yb3+ doped SrWO4 crystal has been grown by the Czochralski method. Polarized absorption and emission spectra together with fluorescent decay curve were measured at room temperature. The stimulated emission cross sections of the potential laser transitions were determined using the reciprocity method and the Fuchtbauer-Ladenberg formula. The potential laser gain versus wavelength for the F-2(5/2) ->-> F-2(7/2) transition was also estimated and discussed. This material is a potential candidate for a 1.0 mu m laser media. (C) 2006 Elsevier B.V. All rights reserved.

Holmium doped sodium gadolinium tungstate crystals with sizes of about 020 mm x 40 mm were grown successfully by the Czochralski technique along the (001) orientation. Polarized absorption spectra, fluorescence spectra and fluorescence decay curve of Ho3+-doped NaGd(WO4)(2) have been recorded at room temperature. Based on the Judd-Ofelt theory, three intensity parameters were obtained. The spectroscopic parameters of this crystal such as the oscillator strengths, radiative transition probabilities, radiative lifetimes as well as the branching ratios were calculated. The fluorescence lifetime tau(f) of the S-5(2) level was measured to be 5 mu s. (c) 2006 Elsevier B.V. All rights reserved.

Dirac-like topological insulators have attracted strong interest in optoelectronic application because of their unusual and startling properties. Here we report for the first time that the pure topological insulator Bi2Te3 exhibited a naturally ultrasensitive nonlinear absorption response to photoexcitation. The Bi2Te3 sheets with lateral size up to a few micrometers showed extremely low saturation absorption intensities of only 1.1 W/cm2 at 1.0 and 1.3 μm, respectively. Benefiting from this sensitive response, a Q-switching pulsed laser was achieved in a 1.0 μm Nd:YVO4 laser where the threshold absorbed pump power was only 31 mW. This is the lowest threshold in Q-switched solid-state bulk lasers to the best of our knowledge. A pulse duration of 97 ns was observed with an average power of 26.1 mW. A Q-switched laser at 1.3 μm was also realized with a pulse duration as short as 93 ns. Moreover, the mode locking operation was demonstrated. These results strongly exhibit that Bi2Te3 is a promising optical device for constructing broadband, miniature and integrated high-energy pulsed laser systems with low power consumption. Our work clearly points out a significantly potential avenue for the development of two-dimensional-material-based broadband ultrasensitive photodetector and other optoelectronic devices.

Enhanced ~3.0 μm emission corresponding to Er3+:4I11/2→4I13/2 was achieved in Nd3+/Er3+ co-doped Lu0.15Y2.85Sc2Ga3O12 (abbr. as Nd,Er:LuYSGG) crystal under 808 nm pumping. As compared with Er:YSGG crystal, the absorption pump efficiency of Nd,Er:LuYSGG crystal is greatly improved and thus ~3.0 μm emission is enhanced by 2.2 times owing to the sensitization of Nd3+, at the same time, Nd3+ as deactivator quenches ~1.5 μm emission from Er3+:4I13/2 level and thus inhibit the self-termination effect successfully. The energy transfer efficiencies of Nd: 4F3/2→Er: 4I11/2 and Er: 4I13/2→Nd:4I15/2 are estimated to be 91.6% and nearly 100%, respectively. These results indicate that the introduction of Nd3+ is very helpful for achieving ~3.0 μm laser in Nd,Er:LuYSGG crystal.

The polarized absorption, emission spectra and the fluorescence decay curve of Er3+ ions in the anisotropic NaY(MoO4)2 crystal were investigated at room temperature, and spectral parameters have been calculated from the absorption data based on the Judd–Ofelt theory. The experimental oscillator strengths for the transitions from the ground state to excited states were compared with the theoretical oscillator strengths calculated from the Judd–Ofelt theory. The emission cross-section and gain cross-section for the π- and σ-spectrum were determined for the 4H13/2 → 4H15/2 transition of special interest for laser application.

Yb3+:GdAl3(BO3)4 (hereafter Yb3+:GAB) crystals with large sizes and good optical quality have been grown by the top-seed solution growth (TSSG) method. The polarized absorption and emission spectra have been investigated at room temperature. For the σ-polarization, the intensities of both absorption and emission spectra are stronger than those for the π-polarization, the σ-absorption cross section of Yb3+ in GAB being 3.43×10-20 cm2 at 977 nm, and the σ-emission cross section being 0.98×10-20 cm2 at 1045 nm. The fluorescence lifetime of the 2 F 5/2→2 F 7/2 transition was measured to be 800 μs in the 5% doped sample used for our laser experiments, 993 μs in a 10% doped sample and 569 μs in a 0.5% doped sample. The laser parameters were estimated as: βmin=0.022, Isat=10.4 kW/cm2 and Imin=0.23 kW/cm2. About 0.4 W laseroutput at the wavelength of 1043 nm was achieved when the Yb3+:GAB crystal was pumped by a 974 nm laser diode, with 27.4% slope efficiency.

The size distributions of different precipitates have been determined for the quantification of precipitates present in the cast martensitic steel G-X12CrMoWVNbN 10-1-1. Direct and indirect methods have been used to discriminate the different precipitates. The former was carried out by images of precipitates from STEM connecting with EDX analysis, and the latter from TEM. The study was performed on the replicas with precipitates which were extracted from the buck steel. Results gained from direct determination are compared with results from indirect determination. It is shown that the total size distributions are in good agreement for both direct and indirect determination in this type of steel. The discrimination and quantification of different precipitates seem to be difficult for indirect method because of uncertainty concerning the quantitative determination of precipitate parameters.

Er3+/Yb3+/Pr3+: CaLaGa3O7 crystal was successfully grown by the Czochralski method. Detailed spectroscopic analyses of Er3+/Pr3+: CaLaGa3O7, Er3+/Yb3+: CaLaGa3O7 and Er3+/Yb3+/Pr3+: CaLaGa3O7 crystals were carried out. Compared with Er3+/Pr3+: CaLaGa3O7 and Er3+/Yb3+: CaLaGa3O7 crystals, Er3+/Yb3+/Pr3+: CaLaGa3O7 crystal not only shows a better absorption characteristic but also exhibits weaker up-conversion and near-infrared emissions, as well as superior mid-infrared emission. Furthermore, the self-termination effect for the 2.7 μm erbium laser is suppressed successfully since the fluorescence lifetime of the 4I13/2 lower level of Er3+ decreases markedly while that of the upper 4I11/2 level falls slightly in Er3+/Yb3+/Pr3+: CaLaGa3O7 crystal. Besides, the sensitization effect of Yb3+ and deactivation effect of Pr3+ ions as well as the energy transfer mechanism in Er3+/Yb3+/Pr3+: CaLaGa3O7 crystal were studied in this work. Moreover, energy transfer microparameters between Yb3+ and Er3+ were also calculated and analyzed based on Dexter's model. In conclusion, the introduction of Yb3+ and Pr3+ is favorable for achieving an enhanced 2.7 μm emission in Er3+/Yb3+/Pr3+: CaLaGa3O7 crystal which can act as a promising candidate for mid-infrared lasers.

We prepared multi-layered MoS2 nanosheets and hierarchical MoS2 nanospheres composed of ultrathin nanosheets via a facile hydrothermal method. The presence of excessive thiourea played a critical role in the formation of nanospheres. Both the passively Q-switched single- and dual-wavelength Yb3+:GdAl3(BO3)4 (Yb:GAB) laser were achieved by using the multi-layered nanosheets and hierarchical nanospheres as saturable absorbers (SAs). As far as we know, the saturable absorption characteristic of hierarchical nanospheres was reported for the first time. Compared with nanosheets, the as-prepared nanospheres SA exhibited improved saturable absorption property with shorter pulse width and higher pulse energy, which should be attributed to the unique hierarchical structure.

In this paper, we reported a multiwavelength passively Q-switched Yb3+:GdAl3(BO3)4 solid-state laser with topological insulator Bi2Te3 as a saturable absorber (SA) for the first time, to the best of our knowledge. Bi2Te3 nanosheets were prepared by the facile solvothermal method. The influence of three Bi2Te3 densities on the laser operation was compared. The maximum average output power was up to 57 mW with a pulse energy of 511.7 nJ. The shortest pulsewidth was measured to be 370 ns with 110 kHz pulse repetition rate and 40 mW average power. The laser operated at three wavelengths simultaneously at 1043.7, 1045.3, and 1046.2 nm, of which the frequency differences were within the terahertz wave band. Our work suggests that solvothermal synthesized Bi2Te3 is a promising SA for simultaneously multiwavelength laser operation.

In order to make accurate forecasts of mobile internet diffusion trend, this paper proposes a method which is based on modified bass innovation diffusion model in which the values of three parameters change over time. A novel particle swarm optimisation (PSO) algorithm is introduced to find the most precise parameters. This algorithm employs opposition-based learning strategy during the stage of initialisation and execution. The application of the index of population density helps determine the convergence status of population, and inertia weight is adjusted dynamically according to the value of population density. When the algorithm is trapped into local optima, the combination of Cauchy mutation and Gaussian mutation is applied on the best particle. The results demonstrate good performance of the novel algorithm on convergence accuracy and convergence velocity and the modified Bass model has the capability to forecast the diffusion of mobile internet more accurately.

In this work, we report on the spectroscopic properties of Dy3+ doped YAlO3 crystal grown by Czochralski technique. The Judd-Ofelt theory was performed based on the measured polarized absorption spectra. Under optical pumping at 1300 nm, Dy:YAP crystal exhibited a broad MIR emission centered at 3020 nm, with a bandwidth of 520 nm at full width half maximum. The decay lifetime of the 6H13/2 level was measured to be 8.88 ms, and the corresponding quantum efficiency evaluated was 57.9%. The studied optical gain properties indicate that Dy:YAlO3 crystal could be a potential candidate for solid-state mid-infrared laser applications.