Spectral properties of Tm,Ho:LiYF4 laser crystal

The LiYF4 single crystal codoped with thulium and holmium ions was successfully grown by the Cz method. The optimal technical parameters obtained were as follows: the pulling rate was 0.16 mm/h; the rotation speed was 3 rpm; the cooling rate was 15 °C/h. The result of XRD curve showed that as-grown Tm,Ho:LiYF4 laser crystal belonged to the monoclinic system with scheelite-type structure and space group I41/a. The cell parameters calculated were: a=0.52160 nm, c=1.09841 nm and Z=4. Absorption and fluorescence spectra of Tm,Ho:LiYF4 laser crystal at room temperature were measured and analysed. The absorption cross section, FWHM and absorption coefficient at 779.3 nm calculated were 7.44×10-21 cm2, 8.7 nm and 2.23 cm-1, respectively. An intensive fluorescence emission peak appeared near 2045 nm. The emission cross section and fluorescence lifetime were 0.87×10-20 cm2 and 10.8 ms, respectively. The ratio of Tm-Ho transfer to its back-transfer process was 10.6.     

Paramagnetic Anisotropy of CdGd2(WO4)4-δ Single Crystal

CdGd2(WO4)4-δ single crystal was grown using the Czochralski's method. The crystal structure was tetragonal scheelite with lattice parameters a=b=0.5203 nm and c=1.1359 nm. There were vacancies of (WO4)2-, therefore, there were some Gd2+ ions. Langevin paramagnetism and anisotropy were observed from the σ-T curves at room temperature. The susceptibility χ// was 3.5018×10-3, and χ⊥ was 3.4403×10-2. The anisotropy was also observed in the electron spin resonance (ESR) experiments. The anisotropic Landé factors were g//=2.1333 and g⊥=2.8411. The direction of easy magnetization was in the a-b plane. Anisotropic paramagnetic Curie constants C// and C⊥ were not only related to macroscopic σ that was observed through the experiment, but were also related to J⊥ and J//, which were the microscopic quantum numbers of the Gd2+ and Gd3+ ions. Based on the detailed analyses, the proportion of 36.8% of Gd3+ ions to 63.2% of Gd2+ ions in the Gd ions of the CdGd2(WO4)4-δ crystal was calculated, and δ was 0.638 in the single crystal.     

Growth and spectral characteristics of a new promising stoichiometric laser crystal: Ca9Yb（VO4）7

A Ca9Yb(VO4)7 crystal with dimensions of Φ23 mm×35 mm was grown successfully by Czochralski method. Its thermal conductivity was 1.06 W/(m?K) at room temperature. The absorption cross-sections at 980 nm were 1.80×10–20 cm2 and 1.28×10–20 cm2 for π- and σ- polarizations, respectively, with a full-width at half-maximum of 34 nm. The crystal had a broad emission at around 1025 nm with a full-width at half-maximum of 67 nm for π- polarization and 70 nm for σ- polarization. The emission cross-sections of the crystal were calculated by using reciprocity method and Füchtbauer-Ladenburg formula. The emission cross-sections at 1025 nm were 3.57×10–20 cm–2 and 1.91×10–20 cm–2 for π- and σ- polarization, respectively. The fluorescence lifetime was 332 μs. The results indicated that the crystal is a promising femtosecond and tunable laser material.     

Growth,structure and spectral characteristics of KEr_(0.1)Yb_(0.9)(WO_4)_2 laser crystal

The 10 at.% Er3+-doped KYb(WO4)2(KEr0.1Yb0.9(WO4)2) laser crystal with dimensions up to 25 mm×15 mm×10 mm was grown by the Kyropoulos method.The crystal structure was identified as β-KEr0.1Yb0.9(WO4)2 by XRD analysis.Through TG-DTA curves,the melting point and transition point of the crystal were determined to be 1058 and 1031 °C,respectively.Infrared spectrum and Raman spectrum were measured,and the vibration frequencies of infrared and Raman active modes for the crystal were assigned.The absorption cross section is 3.1×10-20 cm2 at chief peak of 981 nm with the absorption line width of 26 nm.Based on the Judd-Ofelt theory,the intensity parameters ?λ(λ=2,4,6) calculated were:?2=16.34×10-20 cm2,?4=4.18×10-20 cm2,and ?6=1.26×10-20 cm2.There was a strong emission peak near 1533 nm and the emission line width at the main peak at 1533 nm run up to 55 nm with the emission cross section of 3.47×10-20 cm2 .These optical parameters indicated the potential of this crystal used as an excellent laser material for 1540 nm nearby human-eye safe.     

Crystal growth and spectral characterizations of Ho~(3+)-doped Li_3Ba_2La_3(MoO_4)_8 crystal

A large Ho~(3+):Li_3Ba_2La_3(MoO_4)_8 crystal with high optical quality and well-developed appearance was grown by the flux method. The main spectral properties of the crystal, including the absorption spectra, fluorescence spectra and fluorescence decay curves were recorded at room temperature. The Judd-Ofelt(J-O) theory was applied to calculate the oscillator strength parameters Ω_t(t=2, 4, 6), spontaneous emission probabilities, fluorescence branching ratios, and radiative lifetimes of Ho~(3+) ions undergoing transitions from ground state ~5I_8 to the excited states. The stimulated emission cross-section for the ~5I_7→~5I_8 transition was estimated to be 1.32×10~(–20) cm~2 at 2045 nm by Fuchtbauer-Ladenburg(F-L) equation and the quantum efficiency of the ~5I_7 level was calculated to be 89%.     

Growth,structural, spectral and high-power continuous-wave laser operation of Yb_(0.11)Gd_(0.89)COB crystal

A Yb_(0.11)Gd_(0.89)Ca_4O(BO_3)_3 crystal with new composition was grown by the Czochralski method. The crystal structure was measured and analyzed. The unit-cell parameters of the Yb_(0.11)Gd_(0.89)COB were calculated to be a=0.8089(7) nm, b=1.5987(6) nm, c=0.3545(8) nm, β=101.22o. The absorption and fluorescence spectra were measured. The maximum absorption cross-section of Yb_(0.11)Gd_(0.89) COB crystal was 0.79×10~(–20)cm~2, which occurred at 976 nm with Y polarization. The emission cross-section at 1027 nm was calculated to be 0.33×10~(–20) cm~2. The radiative lifetime trad was calculated to be 2.74 ms. The Stark energy-level diagram of Yb~(3+)in the Yb_(0.11)Gd_(0.89)COB crystal field at room temperature was determined. The ground-state energy level ~2F_(7/2) splitting was calculated to be as large as 1004 cm~(–1) and the zero-line energy was 10246 cm~(–1). A maximum output power of 9.35 W was achieved in continuous-wave(CW) mode, with the slope efficiency being 42.1%. Chemical etching experiment revealed that the dominating imperfections in the studied Yb_(0.11)Gd_(0.89) COB crystal were dislocations and sub-grain boundaries. The existence of crystal defects could cause light scattering, and degrade laser output efficiency. The influence of crystal defects on laser properties was discussed.     

Growth and Characteristic of YbAl3(BO3)4 Crystal

YbAl3(BO3)4 crystal of good optical quality was grown by the flux method. The structure of YbAl3(BO3)4 crystal was determined by single-crystal X-ray diffraction. The experiment shows that YbAl3(BO3)4 belongs to the double borates with a trigonal structure. The space group is R32 and its unit cell constants were measured to be a=0.92965 nm, c=0.72129 nm, V=0.53673 nm3, Z=3. The transmittance spectra were measured. The cut-off of YbAl3(BO3)4 crystal is 216 nm, and there are two absorption peaks located at 940 and 975 nm from 190 nm to 2600 nm. The thermal properties of YbAl3(BO3)4 crystal were studied for the first time. The average thermal expansion coefficients were determined to be 2×10-6/℃, 9.5×10-6/℃ along a- and c- direction. The specific heat of YbAl3(BO3)4 crystal was measured to be 0.6695 J·(g·℃)-1 at room temperature. All results indicate that the YbAl3(BO3)4 crystal is an excellent stoichioimetric laser material.     

Polarized spectral analysis of Er3+ ions in Er3+/yb3+:LiLa(MoO4)2 crystal

Optical characteristics and upconversion dynamics of Er3+ in Er3+/Yb3+:LiLa(MoO4)2 crystals were investigated. The absorption spectra, fluorescence spectra and the fluorescence decay curves were analyzed at room temperature. The infrared emission at 1538 nm and visible emissions at 520–569 and 640–670 nm, corresponding to 2H11/2,4S3/2→4I15/2 and 4F9/2→4I15/2 transitions of Er3+ ions, were simultaneously observed in Er3+/Yb3+:LiLa(MoO4)2 crystals under 976 nm excitation at room temperature. The maximal emission cross-section near 1530 nm for π-polarization was 0.63×10–20 cm2 and the measured lifetime of 4I13/2 was 4.88 ms. The upconversion process was involved in sequential two-phonon processes, either the energy transfer from Yb3+ ions or by the excited state absorption.     

Paramagnetic Anisotropy of CdGd2（WO4） 4-δ Single Crystal

CdGd2 （WO4）4 -δ single crystal was grown using the Czochralski＇s method. The crystal structure was tetragonal seheelite with lattice parameters a = b = 0.5203 nm and c = 1. 1359 nm. There were vacancies of （WO4）^2- , therefore, there were some Gd^2＋ ions. Langevin paramagnetism and anisotropy were observed from the δ-T curves at room temperature. The susceptibility X//was 3.5018×10^-3, and X⊥ was 3.4403× 10^-2. The anisotropy was also observed in the electron spin resonance （ESR） experiments. The anisotropic Land6 factors were g//= 2. 1333 and g~ = 2. 8411. The direction of easy magnetization was in the α-b plane. Anisotropic paramagnetic Curie constants C//and C⊥ were not only related to macroscopic a that was observed through the experiment, but were also related to J⊥ and J//, which were the microscopic quantum numbers of the Gd^2＋ and Gd^3｜ ions. Based on the detailed analyses, the proportion of 36.8% of Gd^3＋ ions to 63.2% of Gd^2＋ ions in the Gd ions of the CdGd2（WO4）4-δ crystal was calculated, and δ was 0.638 in the single crystal.     

Optical and thermoluminescence properties of Lu2Si2O7：Pr single crystal

Single crystal of Lu2Si2O7:Pr was grown by Czochralski method. Transmittance, photoluminescence excitation (PLE) and photo-luminescence (PL) spectra, X-ray excited luminescence (XEL) and fluorescence decay time spectra of the sample were measured and discussed to investigate its optical characteristics. The crystal structure of the as grown Lu2Si2O7:Pr was confirmed to be C2/m. There was a broad absorption peaking at 245 nm in the region from 200-260 nm. The PL spectrum was dominated by fast 3PJ→3HJ band peaking at 524 nm. The XEL spectrum was dominated by the fast 5d14f1→4f2 emission peaking at 265 nm. The 2D (temperature-intensity) and 3D (temperature-wavelength-intensity) thermally stimulated luminescence (TSL) spectra were measured. The Pr3+ ion was found to be the recombination center during the TSL process. Three obvious traps were detected in LPS:Pr single crystal with energy depth at 1.06, 0.78 and 0.67 eV.     

Up-conversion luminescence from Nd~(3+) ions doped in NaBi(WO_4)_2 single crystal

The luminescence of Nd3+-doped in NaBi(WO4)2 single crystal was investigated from 10 K to room temperature.The excitation source was a pulsed dye laser in resonance into the(4G5/2+2G(1)7/2) levels of Nd3+ ions.Several blue emission bands in the up-conversion luminescence spectra corresponded to transitions from 2P1/2 to 4I9/2.Some violet bands corresponding to transitions of 4D3/2→(4I9/2,4I11/2,4I13/2) were also observed.For comparison,the luminescence spectra and decay curves excited by the pulsed 355 nm l...     

Study on Growth and Spectra Properties of Nd: GGG Crystal

The laser crystal Nd GGG was grown by Cz method. The optimum processing parameter is that the pulling rate is 2~4mm·h-1, the rotation rate is 20~40 r·min-1 and the cooling rate is 20℃. The absorption and fluorescence spectra of Nd GGG were measured. The main absorption peak of Nd GGG is at 808 nm and the fluorescence emission peak is at 9430cm-1, corresponding to 4F3/2-4I11/2 emission band of Nd3 ions.     

Photoluminescence properties of Tm~(3+)/Tb~(3+)/Sm~(3+)tri-doped Na_5Y_9F_(32)single crystal with high thermal stability for white light-emitting diodes

A novel Tm~(3+)/Tb~(3+)/Sm~(3+)tri-doped Na_5 Y_9 F_(32) single crystal was synthesized by a modified Bridgman method for the propose of white light emitting diodes.The fluorescence spectra of various Sm~(3+)ion concentrations and fixed 0.4 mol% Tm~(3+) and 0.5 mol% Tb~(3+) were measured and studied systematically excited by near-ultraviolet light of 355 nm.The Sm3+ion concentration takes apparent effect on the relative intensity of peaks in the visible region and the color coordinate combining from these emission bands.A near pure white light emission with color coordinates(0.3295,0.3057) and color temperature(5657 K) can be obtained when the concentrations of Tm~(3+),Tb~(3+) and Sm~(3+) ions are 0.4 mol%,0.5 mol%and 0.8 mol%,respectively.Furthermore,the practical down-conversion internal quantum yield was measured by integrating spheres at about 14.39%.The tri-doped Na_5 Y_9 F_(32) single crystal shows a high thermal stability inferring from the temperature dependent emission in which the integrated emission intensities are reduced only by～3% with the increase of temperature from 280 to 450 K.The present results demonstrate that the Tm~(3+)/Tb~(3+)/Sm~(3+)tri-doped Na_5 Y_9 F_(32) single crystal may provide a promising candidate for white light-emitting diodes,luminescent materials and fluorescent display devices.     

Mechanisms of Fluorescence Quenching of Pr^3＋-Doped PbWO4 Crystal

Fluorescence decay curves of the ^3P0 and ^1D2 manifolds in Pr^3＋ doped PbWO4 crystal were measured at room temperature and fluorescence lifetimes of both manifolds were estimated. Combining with the radiative lifetimes of the manifolds calculated on the basis of the modified J-O theory, the main mechanisms for the fluorescence quenching of the manifolds were analyzed. The multi-phonon relaxation and the cross-relaxation energy transfer are the major reasons for the fluorescence quenching of the ^3P0 and ^1D2 manifolds, respectively. The Inokuti-Hirayama model was used to analyze the fluorescence decay curve of the ^1D2 manifold and the cross-relaxation of dlpole-dipole interaction was confirmed. Consequently, the ^3p0 manifold is more favorable as an upper laser level than the ^1D2 manifold.     

Growth and characterization of new laser crystal Nda3＋：ca2.85Gd0.1（VO4）2

The crystal growth, crystal defect, thermal properties and luminescence properties of Nd3+:Ca2.85Gd0.1(VO4)2 were investigated. Nd3+:Ca2.85Gd0.1(VO4)2 crystal grown by Czochraski method was green colored, and was not transparent, which was possibly due to residual impurities in V2O5, or due to the lack of oxygen in the growth process. And the Nd3+:Ca2.85Gd0.1(VO4)2 crystal had the existence of 180° do-mains. However, the annealing method could effectively decrease the crystal defect and greatly improve the quality of crystal. The average thermal expansion coefficients calculated were α⊥c=9.5767×10-6 K-1, α∥c=10.7647×10-6 K-1, respectively. The specific heat of Ca2.85Gd0.1(VO4)2 was 0.401 J/(g·K) at 330 K. The polarized absorption spectra and the polarized fluorescence spectra of Ca2.85Gd0.1(VO4)2 were measured at 330 K. Based on the Judd-Ofelt theory, the intensity parameter Ωλ (λ=2, 4, and 6), the radiation transition probabilities τrad, the stimulated-emission cross section σp in Nd3+:Ca2.85Gd0.1(VO4)2 crystal were calculated.     

Growth and Spectral Properties of Crystal Er^3＋ ：Y0.5Gd0.5VO4

Er^3＋ ：Y0.5Gd0.5VO4 crystal with good optical quality was grown by Czochraski method. The structure of the crystal was determined by X-ray powder diffraction method. The segregation coefficient of Er^3 ＋ ions in the crystal was measured by the ICP method. The absorption and emission spectra were also measured. On the basis of the spectra, the absorption cross-sections, emission spectrum FWHM and fluorescence lifetime of the crystal were calculated. From the properties mentioned above.     

Luminescent Properties of SrGa2S4 :Eu and Its Application in Green-LEDs

Phosphor SrGa2S4Eu2 was synthesized with a high temperature solid state reaction.Its absorption spectrum, photoluminescence spectra, and fluorescence lifetime were studied in details.The excitation spectrum extended from UV to visible light region, and matched the emission of GaN chip.(Sr1-xEux)Ga2S4 emits strong green light and the concentration quenching did not occur; while the thermal quenching was evident.The emission peak shifted to long wavelength with increasing Eu2 concentration because of the changing of the crystal field strength.The lifetime of Eu2 ion was in the order of microsecond, which was reasonable for d→f transition.The electroluminescence spectrum of as-fabricated PC-LED at IF=20 mA was measured and most of the blue light of blue-LED chip at 460 nm was absorbed by the phosphor and simultaneously down-converted into an intensive green light at 540 nm.The color coordinate was (0.32, 0.63).SrGa2S4Eu2 was a promising phosphor for GaN-based green LEDs.     

Crystal structure and infrared spectrum of thallium holmium polyphosphate, TlHo(PO_3)_4

Crystals of thallium-holmium polyphosphate TlHo(PO3)4 were grown by flux method technique and characterized by single crys- tal X-ray diffraction. Structure of TlHo(PO3)4 was solved for the first time, and it crystallized in the monoclinic P21/n space group with the following unit-cell dimensions: a=1.02225(3) nm, b=0.88536(2) nm, c=1.09541(4) nm, β=105.888(1)°, V=0.95354(5) nm3 and Z=4. The crystal structure was solved from 2174 independent reflections with final R1(F2)=0.0442 and Rw(F2)=0.0861 refined with 164 parameters. The atomic arrangement could be described as a long chain polyphosphate organization. Holmium atoms had eightfold coordination. The structure of TlHo(PO3)4 consisted of HoO8 polyhedra sharing oxygen atoms with phosphoric group PO4. Infrared spectrum was investigated at room temperature in the frequencies range, 350–4000 cm–1, showing some characteristic vibration bands of infinite chain structure of PO4 tetrahedra linked by bridging oxygen.     

Process Simulation and Microstructure Analysis of Low Carbon SiMn Quenched and Partitioned Steel

The quenching and partitioning (Q&P) process was experimentally investigated on the thermomechanical simulator (Gleeble3800). The microstructure and fracture mechanism of the sheets were investigated by means of TEM. It was found that the microstructure of quenched and partitioned steel consists of fine lath martensite and thin interlath austenite films. The optimum quenching temperature of producing the maximum amount of retained austenite after final quenching at room temperature was predicted by Matlab software package. It was found that the calculations by Matlab software can provide guidance for experimental processing design reliably. The volume fraction of retained austenite at room temperature was approximately 8%, which was measured easily by the software VC60++ programming. The results verified that quenched and partitioned steel possesses a good combination of strength and plasticity due to its fine microstructure. This steel exhibited high ultimate tensile strength (exceeding 1 000 MPa) and good elongation of 25%. The results showed that the fracture mechanism of the sheets is typical tough fracture under the condition of tensile failure.     

Up-conversion luminescence properties of Yb^3＋ and Ho^3＋ co-doped Bi3.84W0.16O6.24 powder synthesized by hydrothermal method

Using polyethylene glycol (PEG) as the surfactant, Bi3.84W0.16O6.24 up-conversion luminescence nano-crystal co-doped with Yb3+ and Ho3+ ions was synthesized by the hydrothermal method. The structure and properties of luminescence powder were studied by X-ray diffraction (XRD) and scanning electron microscope (SEM). It was of cubic system when the sample was synthesized at a low temperature and the particle size was about 30 nm. The results showed that adding surfactants was useful to improve the powder agglomeration and the grain crystal was spherical. The green emission peak at 546 nm and red emission peak at 655 nm, corresponding to the ( 5F4, 5S2)→ 5 I 8 and the 5 F 5 → 5 I 8 transitions of Ho 3+ , respectively, were simultaneously observed at room temperature under excitation of 980 nm semiconductor laser. The up-conversion luminescence intensity was the strongest when the concentration ratio of Yb3+ /Ho3+ was 6:1 and the concentration of Ho 3+ ion was 1.5 mol.%. The up-conversion mechanism was also studied. The green and red emission peaks were the two-photon absorption according to the relationship between the pump power and the luminescence intensity.