3.1 μm mid-infrared luminescence in Er3+ doped ZnF2 modified aluminum fluoride glass

Herein, melt-quenching and Er³⁺ doping were used to synthesize fluoride glass specimens with low phonon energies (582 cm⁻¹). These glass specimens exhibit intense 3.1 μm mid-infrared band emission when they are excited by a 980 nm laser diode, achieving a full width at half maximum (FWHM) of about 166 nm. This 3.1 μm emission intensity is enhanced by the introduction of ZnF₂ to the AlF₃-based fluoride glass. Up-conversion emission, strong near-infrared emission, and fluorescence lifetime are enhanced to different degrees by increasing the ZnF₂ content. Moreover, the spectroscopic characteristics of the glass specimens and the highly efficient Er³⁺: ⁴S_3/2 → ⁴F_9/2 transition's energy transfer mechanism were investigated. The absorption spectra and emission spectra of these aluminum fluoride glass specimens were used to calculate their gain coefficients and maximum cross sections at 1.5 and 3.1 μm. Overall, the spectral properties of these prepared aluminum fluoride glass specimens demonstrate their high potential for use as infrared laser host materials.     

Gd3+ ion induced UV upconversion emission and temperature sensing in Tm3+/Yb3+:Y2O3 phosphor

Cubic phase Tm³⁺/Yb³⁺:Y₂O₃ and Tm³⁺/Yb³⁺/Gd³⁺:Y₂O₃ phosphors were prepared by low temperature combustion technique for upconversion emission in UV-visible range.The 980 nm excitation has generated UV emission at 314 nm in tridoped phosphor due to the energy transfer from Tm³⁺ to Gd³⁺ion.Characteristic emission bands from Tm³⁺ are also observed in both the phosphors....     

Synthesis and optical properties of LiNd(PO_3)_4 nanocrystals dispersion in DMSO/TBE

Lanthanide doped nanocrystals with strong fluorescence, long lifetime at high doping concentrations have great potential application in bio-imaging and liquid gain medium. LiNd(PO_3)_4(LNP) crystal was reported to be one of the most excellent laser crystals with high Nd3+ concentration, and their nanocrystals synthesized via improved combustion method for the first time had strong emission intensity and long fluorescence lifetime of 122 μs. Besides,LiNd(PO_3)_4 nanocrystals can be dispersed in mixed solvents of DMSO/TBE(CHBr2 CHBr2) to form a transparent colloidal dispersion, and Judd-Ofelt theory was used to evaluate their optical parameters. In summary, LiNd(PO_3)_4 nanocrystals possess long lifetime(116 μs), low solvents quenching rate(4.9%), large emission cross section(7.63 × 10~(-20) cm~2) and high quantum yield(35.2%) under high Nd3+ ions concentration(1×10~(20) cm~(-3)), which would be the most competitive colloidal gain medium of optical amplification and laser with LD pump and potential biomaterial with low particles concentration.     

Energy transfer process of Nd3+/Ho3+ co-doped fluoride halide glasses with anion substituted multi-wavelength tunable mid-infrared luminescence

Ho³⁺ doped ZBLAN glass with 2.0 and 2.9 μm emission was prepared. In order to further improve the luminescence of Ho³⁺, halogen ions (Cl, Br, I) were introduced to reduce the maximum phonon energy and phonon state density of the sample. At the same time, Nd³⁺ was introduced to transfer the energy to Ho³⁺ pumped with a 793 nm laser (Nd³⁺:⁴F_5/2,⁴F_3/2→Ho³⁺:⁵I₆). The effect of different halogen ion on the luminescent properties of the fluoride halide glass was compared. The results show that the luminescent intensity of infrared increases with the introduction of different halogen ions. By comparison, it is found that the sample with I^– has the strongest luminescence of 1064 nm, 2.0 μm and 2.9 μm. This is consistent with the calculated J-O intensity parameters. In addition, the 2.0 and 2.9 μm emission of Ho³⁺ pumped with a 450 nm laser will not disappear. A mid-infrared sample with multi-wavelength excitation and multi-wavelength emission can be obtained. Nd³⁺/Ho³⁺ co-doped fluoride halide glasses with 1064 nm, 2.0 μm and 2.9 μm luminescence were prepared by melt quenching method. The luminescent mechanism and the energy transfer process between the two ions of Nd³⁺/Ho³⁺ co-doped fluoride halide glass were studied. The J-O parameters, luminescence lifetime and absorption emission cross-sectional area of Ho³⁺ and Nd³⁺ were calculated, respectively. It is found that the value of Ω₂ in the glass matrix increases with the introduction of different halogen ions, while Ω₄ and Ω₆ do not change obviously in different glass compositions. This is because the environment of the crystal field around the rare earth ions changes. The crystal phase and phonon energy of the sample were analyzed by X-ray diffraction pattern and a Fourier transform infrared spectrometer, respectively. Based on the above spectra and data (phonon energy is 634.71 cm⁻¹), it can be predicted that Nd³⁺/Ho³⁺ co-doped fluoride halide glass is a potential mid-infrared luminescent material.     

Nd~(3+)/Yb~(3+) co-doped mid-infrared luminescence fluorobromide glass with energy transfer and zero-thermal-quenching IR emission

Nd~(3+)/Yb~(3+) co-doped fluorobromide glass samples were prepared by melt quenching.The mid-infrared(MIR) luminescence of the Nd~(3+)/Yb~(3+) co-doped fluorobromide glass was investigated by Br-doping reduces the phonon state density of the matrix.The 3.9 μm MIR luminescence of the samples excited at 793 and 980 nm pump excitation was investigated in detail.There is an effective mutual energy transfer process between Nd~(3+) and Yb~(3+).It is proved under 793 nm excitation that the luminescence of Nd~(3+)at 3.9 μm is reduced by effective energy transfer from,Nd~(3+):~2 H_(11/2)→Yb~(3+):~2 F_(5/2),At the same time,it is proved that the effective energy transfer from Yb~(3+):~2 F_(5/2)→Nd~(3+):2 H_(11/2) under the excitation of 980 nm enhances the luminescence of Nd~(3+) at 3.9 μm.In addition,it is found that the samples still have good infrared(IR) luminescent properties when the temperature changes.The emission cross-sectional area and the absorption cross-sectional area are σ_(em)(3.87 × 10~(-20) cm~2) and σ_(abs)(4.25×10~(-20) cm~2).The fluorescence decay characteristics of the sample at 3.9 μm at the ~2 H_(11/2) level were investigated and the fluorescence lifetime was calculated.The gain performance of the sample was calculated and analyzed,which can reach 4.25 × 10~(-20) cm~2.Those results prove that Nd~(3+)/Yb~(3+)co-doped fluorobromide glass is the potential mid-infrared laser gain material.     

CaTiO3–Sm0.9Nd0.1AlO3 ceramics with a moderate dielectric constant and a high quality factor prepared by sol–gel auto combustion method

CaTiO₃–LnAlO₃ (Ln = La, Nd, Sm) is a perovskite-type microwave material system characterized by a moderate dielectric constant ε_r, a high quality factor Q × f, and a small temperature coefficient of resonant frequency τ_f, making this system promising for microwave devices. However, its high synthesis temperature and sintering temperature limit its industrial applications. In our work, single phase 0.7CaTiO₃–0.3Sm_0.9Nd_0.1AlO₃ (7CT–3SNA) was synthesized via the sol–gel auto combustion method using citric acid as fuel at a relatively low temperature. After being calcined at 600 °C for 2 h, well-crystallized 7CT–3SNA powders with 30–50 nm average particle size were achieved, suggesting good sintering activity. The new and narrow order band at about 800 cm⁻¹ in the Raman spectra indicates a high ordering degree in the B site of 7CT–3SNA solid solution. Compared with the solid–state reaction method and co-precipitation method, the 0.7CT–0.3SNA ceramics fabricated by the current method possess a much lower calcination temperature, a similar ε_r value, and an improved Q × f value. The optimum microwave dielectric properties of ε_r = 43.54, Q × f = 54375 GHz, and τ_f = −6.3 × 10⁻⁶/°C are obtained for the CTSA ceramics derived from the sol–gel auto combustion process. Therefore, the 7CT–3SNA ceramics prepared in this study are potential dielectric materials for microwave applications, indicating that the sol–gel auto combustion method is a good alternative strategy for the fabrication of CaTiO₃–LnAlO₃ ceramics.     

Crystal Growth and Laser Characteristics of Nd3+ :KGd(WO4)2

The Nd3 3.2% (atom fraction):KGd(WO4)2 crystal was grown by Kyropoulos method. The absorption spectrum and fluorescence spectrum of Nd3 :KGW crystal were measured. The absorption cross sections at 808 nm(0.6799 ×10-20 cm2) were calculated, and the output wavelength of fluorescence is 1064 and 1351 nm. The diode-pumped laser was operated both in the free-running and passively Q-switched operating modes. The maximum laser output( 1064 nm) is 326mW with 62.7 % slope efficiency when input energy is 900 mW. The beam quality factor M2 ≈ 1.1. The green light of 532 nm is obtained in frequency doubling operation. The laser is passively Q-switched by using Cr4 :LuAG as saturable absorber. The pulse width is 170 ns at repetitive frequency of 15 kHZ.     

Spectral Properties and Upconversion Luminescence of Er^3＋, yb^3＋： BaWO4 Crystal

The optical quality of Er^3＋, yb^3＋： BaWO4 crystal was gown by Czochralski method. Absorption spectra were measured and energy levels were assigned. According to Judd-Ofelt theory, the spectral strength parameters of Er^3＋ ion were fitted to beΩ2 =0.3926 x 10^-20 cm^2, Ω4 =0.0721×10^-20 cm^2, Ω6 =0.0028 ×10.20 cm^2. Emission peaks centered at around 523,544 and 670 nm were observed under 334 nm He-Cd laser excitation and emission peaks centered at 1001 and 1534 nm were detected under 976 nm laser excitation. Strong green emission was also observed when the crystal was pumped with 808 nm and 976 nm laser. The mechanisms of frequency upconversion and sensitization were analyzed.     

Y4GeO8:Er3+,Yb3+ up-conversion phosphors for optical temperature sensor based on FIR technique

Herein, we reported novel Y₄GeO₈:Er³⁺,Yb³⁺ phosphors elaborated via conventional solid-state reaction, and we further explored their properties as optical thermometer by using fluorescence intensity ratio (FIR) method complemented by detailed analysis on crystal structure, up-conversion luminescence and energy transfer from Yb³⁺ to Er³⁺. Upon 980 nm laser excitation, Y₄GeO₈:Er³⁺,Yb³⁺ phosphors present 525, 547 and 659 nm emission bands assigned to the characteristic transitions of Er³⁺. Furthermore, Y₄GeO₈:Er³⁺,Yb³⁺ samples show outstanding temperature sensing performances. To be specific, the minimal temperature resolution is 0.03 K (303 K), and the relative sensitivity of FIR can be up to 1.152%/K (303 K). Hence, Y₄GeO₈:Er³⁺,Yb³⁺ phosphors can be possible candidates for thermometry devices.     

Synthesis and Spectral Properties of Nd^3＋： Gd3Ga5O12 Nanopowder for Transparent Laser Ceramics

Nd^3＋： Gd3Ga5O12（Nd ： GGG） nanopowder for transparent laser ceramics was synthesized using sol-gel method. XRD, SEM, and fluorescence spectrum were used to study the properties of Nd^3＋ ：Gd3Ga5O12 nanopowder. XRD patterns of samples show that it has a cubic structure. Meanwhile, pure Nd：GGG crystals were obtained at 1000 ℃ for 12 h. SEM photographs show that dispersed, uniform, ball-like Nd：GGG nanopowder is obtained. Both XRD and SEM results show that the crystallization degree and the grain size increase with the increase in calcining temperature. Analysis of fluorescence spectrum shows that fluorescence emission occurs at 1062.7 nm, which is the result of Nd^3＋ （^4F3/2→^4I11/2） transition. Homogenous Nd ： GGG nanopewder with a small grain size synthesized using the sol-gel method is favorable for sintering the transparent ceramic, which proves that the nanopewder obtained is suitable as a precursor for preparing GGG transparent ceramics.     

Plastic properties of Cu2O,mechanical tests and transmission electron microscopy—II. High temperature

Creep tests have been performed on Cu₂O at temperature from 700°C (0.64 T_M) to 1060°C (0.88 T_M), stresses from 2 MPa (σ/θ ∼- 2 × 10⁻⁴) to 24 MPa (σ/θ ∼- 2.4 × 10⁻³) and oxygen partial pressures from 10⁻¹ Pa to 10⁴ Pa. A creep law has been established for polycrystals and single crystals compressed along 〈001〉, 〈011〉 and 〈111〉. Microstructural observations including transmission electron microscopy, show the build up of a polygonized substructure typical of high temperature steady state creep. This allows to conclude in favour of a creep kinetics controlled by a dislocation climb recovery of the microstructure, the elementary process being the oxygen diffusion.     

Hydrogen detrapping from grain boundaries and dislocations in high purity iron

Hydrogen detrapping in high purity iron was studied by measuring evolution rates of quenched-in hydrogen from 80 to 800 K using a quadrupole mass spectrometer in an ultra high vacuum system. The peak of the evolution rate was observed at 395 K in single crystal specimens and 415 K in polycrystalline specimens with a heating rate of 1 K min⁻¹. Effects of grain size and deformation on the evolution rate was also studied. It was shown that the results are consistent with the evolution rates calculated with the binding energy B = 0.51 ± 0.02 eV and the trap density term γC_{T = (4 ∼ 15) × 10⁻⁵} in polycrystalline iron, and B = 0.47 ± 0.02 eVand γC_T = (2 ∼ 13) × 10⁻⁵ in single crystal iron. The dominant traps are considered to be grain boundaries in polycrystalline specimens and dislocations in single crystal specimens.     

Optical,thermal and luminescence properties of La2O3–Ga2O3–ZrO2 glasses co-doped with Tm3+/Yb3+ prepared by containerless technique

Bulk La₂O₃–Ga₂O₃–ZrO₂ (LGZ) glass and Tm³⁺/Yb³⁺ co-doped LGZ glasses were synthesized successfully using containerless technique. Raman spectra result reveals that the matrix sample possesses the low maximum phonon energy of ～642 cm^?1. The glasses show good compatibility between large Abbe numbers (>31) and high refractive indices (n_d > 1.93). Moreover, transmittance measurements reflect that the glasses have high infrared transmittance of ～81.9%, small OH^– absorption coefficient and long mid-infrared cut-off wavelengths (～7.5 μm). The surface morphology of host glass was characterized by scanning electron microscopy (SEM) micrograph and energy dispersive spectroscopy (EDS) tests reflect that the doped compositions are distributed into the matrix glass homogeneously. The results of thermal analysis show that the glasses have good thermal properties (T_g > 769 °C). Excited by 980 nm laser, an intense 1810 nm fluorescence is obtained originating from the transition: ³F₄ → ³H₆ of Tm³⁺ ion, accompanied by upconversion emission. It can be observed that 1810 nm fluorescence has the highest intensity at 1 mol% Yb₂O₃ and owns broad full width at half-maximum (>245 nm), the luminescence intensity of ³F₄ → ³H₆ transition increases with rising temperature from 300 to 550 K. Furthermore, the value of energy transfer efficiency shows that Yb³⁺ can transfer energy to Tm³⁺ effectively. By fitting the attenuation curves, the lifetimes of 1810 and 474 nm emission can be acquired.     

Temperature dependent behaviors of electro-elastic properties of NdCa4O(BO3)3 crystal with monoclinic symmetry

Rare-earth calcium oxyborate crystals (RECa₄O(BO₃)₃, RECOB, RE: rare-earth elements) are a kind of multifunctional crystal materials. In this work, the temperature dependent behaviors of the electro-elastic constants of NdCOB crystal were investigated over the temperature range of –80–200 ℃, and their temperature coefficients were evaluated. It is found that NdCOB crystal possesses minimal variation of relative dielectric permittivities (<3%). The temperature coefficient of frequency for ZY cut with width shear vibration mode is in the order of 0.07 × 10^?4/℃. The temperature coefficients of the elastic compliances are obtained to be in the range of ?33.0 × 10^?4/℃–32.2 × 10^?4/℃. Particularly, the s₄₄ and s₆₆ were found to show low temperature coefficients of the elastic compliances, i.e. 1.0 × 10^?4/℃ and ?0.4 × 10^?4/℃, respectively, indicating the existence of zero temperature coefficient of frequency crystal cut. Furthermore, the electromechanical coupling factors and piezoelectric coefficients as a function of temperature were studied. The electromechanical coupling factor k₂₆ and piezoelectric coefficient d₂₆ are determined to be ～30.8% and ～15.2 pC/N at room temperature, respectively. The large piezoelectric response and zero temperature coefficient of frequency indicate the potential usage of NdCOB crystal for piezoelectric frequency devices over a wide temperature range.     

X-ray diffraction analysis by Rietveld refinement of FeAl alloys doped with terbium and its correlation with magnetostriction

Fe₈₁Al₁₉ polycrystalline alloys doped with Tb(0-0.25 at%) were obtained by arc melting.The introduction of Tb favors the formation of columnar grains in the micro structure of the alloys,which develops a texture in the [100]crystal direction.Microstructural examination shows that the alloys are composed in great proportion by the disordered body-centered cubic(bcc),A2 phase and by a small proportion of the ordered bcc,B2 phase.As a consequence of doping with Tb,the lattice ...     

Crystal Growth and Spectral Properties of Yb^3＋ ：KY（WO4 ）2

Laser crystal Yb:KYW was grown by the Kyropoulos method. A grown crystal was identified as β-Yb:KYW by XRD. By TG-DTA the melting point and transition point of the crystal are 1045 and 1010 °C, respectively. Infrared spectrum and Raman spectrum were measured, and the vibrational frequencies of infrared and Raman active modes for Yb:KYW crystal were assigned. Absorption spectrum of Yb:KYW shows that there are two intensive absorption peaks at 940 and 980 nm, respectively, and the absorption cross section is 1.34 × 10⁻¹⁹ cm² at chief peak of 980 nm. There exist three intensive emission peaks in Yb:KYW at 990, 1010 and 1030 nm, respectively, and the emission line width of the chief peak 1030 nm runs up to 16 nm. It was calculated that the peak emission cross section is 3.1 × 10⁻²⁰ cm² at 1030 nm.     

Anti-corrosion performance of Si-surface-alloying NdFeB magnets obtained with magnetron sputtering and thermal diffusion

Si alloying in the surface layer of NdFeB magnets was realized by thermal diffusion combined with magnetron sputtering. The surface composition, phase structure and morphology of NdFeB(S–Si) specimens were characterized by an X-ray diffractometer, an X-ray photoelectron spectrometer and a field emission scanning electron microscope, respectively. The corrosion resistance of bare NdFeB(S–Si) was analyzed by static full immersion corrosion test and electrochemical experiments. Effects of sputtering and thermal diffusion on the microstructure and corrosion resistance of the surface layer were studied. Results show that surface alloying layer can effectively improve the corrosion resistance of bare NdFeB with the optimized static total immersion corrosion test time in NdFeB(1S–Si)-800 of 36 h, which is much longer than that of the pristine NdFeB (less than 0.5 h). The E_corr of NdFeB(1S–Si)-800 positively shifts from −1.05 to −0.92 V, indicating that the corrosion tendency is obviously lower. The J_corr is 1.45 × 10⁻⁶ A/cm² which is 2 orders of magnitude lower than that of the pristine NdFeB (5.25× 10⁻⁴ A/cm²). The intergranular composite oxides existing in Nd-rich phase contribute to the enhancement of corrosion resistance of Si-surface-alloying NdFeB.     

Pressure and temperature dependent up-conversion properties of Yb3＋-Er3＋ co-doped BaBi4Ti4015 ferroelectric ceramics

Yb^3＋ and Er^3＋ co-doped BaBi4Ti4015 （BBT） ceramic samples showed brighter up-conversion photoluminescence （UC-PL） under excitation of 980 nm. The monotonous increase of fluorescence intensity ratio （FIR） from 525 to 550 nm with temperature showed that this material could be used for temperature sensing with the maximum sensitivity to be 0.0046 KI and the energy dif- ference was 700 cm-1. Moreover, the sudden change of red and green emissions around 400 ℃might imply a phase transition. With increasing pressure up to 4 GPa, the PL intensity decreased but was still strong enough. These results illustrated the wide applications of BBT in high temperature and high pressure conditions.     

Efficient improvement of 2.7 μm luminescence of Er~(3+):oxyfluoride glass containing gallium by Yb~(3+) ions codoping

Mid-infrared laser materials with low phonon energy have significant applications. However, the development of available glass systems for high-power laser gain medium have posed a great challenge.Therefore, we investigated the 2.7 μm spectroscopic properties of Er~(3+)/Yb~(3+) -codoped oxyfluoride glass containing gallium, which were prepared by typically melting and quenching methods. The 2.7 μm luminescence properties of the Er~(3+)/Yb~(3+)-codoped oxyfluoride glass containing gallium were recorded by a 980 nm laser diode. The Judde Ofelt parameters, decay curves, emission cross section, energy transfer efficiency and quantum efficiency were calculated. The maximum emission cross section of YbFGa-0.5 is 1.63 × 10~(-20) cm~2 by 980 nm excitation. The energy transfer efficiency is calculated to be77.8% for the YbFGa-0.5 glass around 2700 nm. The quantum efficiency at 1530 nm is 65.6%. The result reveals that the best doping concentration ratio of Er~(3+):Yb~(3+) ions is 1:0.5, and suggests an effective energy transfer from Yb~(3+) to Er~(3+) ions.     

Magnetic property recovery in Nd-Fe-B bonded magnet wastes with chemical reaction and physical dissolution

The main difficulty for the recovery of Nd-Fe-B bonded magnet wastes is how to completely remove the epoxy resins. In this study, chemical reaction and physical dissolution were combined to remove the epoxy resins by adding ammonia-water and mixed organic solvents. Ammonia-water can react with the epoxy functional group of epoxy resin to generate polyols. Mixed organic solvents of alcohol, dimethyl formamide (DMF), and tetrahydrofuran (THF) can dissolve the generated polyols and residual epoxy resins. Under the optimum processing conditions, the epoxy resins in the waste magnetic powders are substantially removed. The oxygen and carbon contents in the recycled magnetic powder are reduced from 13500 × 10⁻⁶ to 1600 × 10⁻⁶ and from 19500 × 10⁻⁶ to 2100 × 10⁻⁶ with the reduction ratio of 88.1% and 89.2%, respectively. The recycled magnetic powder presents improved magnetic properties with M_s of 1.306 × 10⁻¹ A∙m²/g, M_r of 0.926 × 10⁻¹ A∙m²/g, H_cj of 1.170 T, and (BH)_max of 125.732 kJ/m³, which reach 99.8%, 99.4%, 95.9%, and 96.9% of the original magnetic powders, respectively.