Crystal growth and spectral analysis of Dy3+ and Er3+ doped KPb2Cl5 as a mid‐infrared laser crystal

This paper reports crystal growth and optical characteristics of dysprosium (Dy³⁺) and erbium (Er³⁺) doped mid‐infrared laser crystal ternary‐potassium‐lead‐chloride (KPb₂Cl₅). Two transparent crystals with good optical quality have been grown successfully by using the Bridgman technique,the largest crystal size reaches up to ∅︁10×60mm². Measurements of X‐ray diffraction(XRD) and absorption spectra were carried out. Based on Judd‐Ofelt theory, the intensity parameters Ω_t(t=2,4,6), the experimental and theoretical oscillator strengths have been obtained.The intensity parameters Ω_t(t=2,4,6) of Er³⁺:KPb₂Cl₅ were calculated to be Ω₂=5.10×10^‐20 cm², Ω₄=1.25×10^‐20 cm², Ω₆=0.83×10^‐20 cm², and the values for Dy³⁺:KPb₂Cl₅ were calculated to be Ω₂=6.26×10^‐20 cm², Ω₄=2.45×10^‐20 cm², Ω₆=0.04×10^‐20 cm² respectively. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Crystal growth and spectral properties of Nd:Ca5(BO3)3F

A neodymium doped Ca₅(BO₃)₃F single crystal with size up to 51×48×8 mm³ has been grown by the top seeded solution growth (TSSG) technique with a Li₂O‐B₂O₃‐LiF flux. The spectra of absorption and fluorescence were measured at room temperature. According to Judd‐Ofelt (J‐O) theory, the spectroscopic parameters were calculated and the J‐O parameters Ω₂, Ω₄, Ω₆ were obtained as follows: Ω₂ = 1.41×10⁻²⁰cm², Ω₄ = 3.18×10⁻²⁰cm², Ω₆ = 2.11×10⁻²⁰cm². The room temperature fluorescence lifetime of NCBF was measured to be 51.8 μs. According to the J‐O paramenters, the emission probabilities of transitions, branching ratios, the radiative lifetime and the quantum efficiency from the Nd^{3+ 4}F_3/2 metastable state to lower lying J manifolds were also obtained. In comparasion with other Nd‐doped borate crystals, the calculated and experimental parameters show that NCBF is a promising SFD crystal.     

Spectroscopic properties of La3Ga5SiO14:Er3+ (1%) crystals

Single crystals of Erbium (Er) doped La₃Ga₅SiO₁₄ (LGS) have been grown along c‐axis by using the Czochralski method. The absorption and fluorescence spectra of LGS: Er³⁺ single crystals have been measured and analyzed according to the Judd‐Ofelt theory. When applied, the following spectral parameters have been obtained: intensity parameters Ω_t, Ω₂= 2.741674×10^‐20cm², Ω₄= 0.66934×10^‐20 cm² and Ω₆= 0.592591×10^‐20 cm², radiative transition probabilities A_J,J”, P_J,J”. The radiative lifetime of levels ⁴I_13/2, ⁴H_9/2, ⁴S_3/2 are 11.333ms, 0.447ms and 0.704ms, respectively. The fluorescence branching ratios and the integrated emission cross sections are also calculated. The results suggest that LGS: Er crystals have potential applications as a laser material. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Growth of Nd:Sr3Ga2Ge4O14 crystals by a modified Bridgman method

Bridgman growth of Nd:SGG (Sr₃Ga₂Ge₄O₁₄) crystals has been investigated for the first time. Pt crucible of ∅︁25mm×250mm with a seed well of ∅︁10mm×80 mm is used, and seed is SGG crystal of ∅︁10mm×50mm grown by Bridgman method in advance. The growth parameters are optimized as the furnace temperature is set to 1450∼1500°C, temperature gradient in the crystal‐melt interface is less than 25 K/cm and growth rate is less than 0.5mm/h. The Nd:SGG crystals with 25mm in diameter and 60mm in length are grown successfully from 1.5 to 8at% Nd³⁺ doped stoichiometric Sr₃Ga₂Ge₄O₁₄ melt. The distribution coefficient and concentration of Nd³⁺ in Nd:SGG crystals are obviously higher than those of Nd:YAG crystal. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Effect on the fluorescence branching ratio of different synergistic ligands in neodymium complex doped PMMA

A series of neodymium complexes Nd(TTA)₃L_x (where TTA = α-thenoyltrifluoroacetonato, L_x (x = 1–5) = H₂O, triophenylphosphine oxide (Tppo), 2,2-bipyridine (Bipy), 1,10-phenanthroline (Phen) and 2- (N,N-diethylanilin-4-yl)-4,6-bis(3,5-dimethylpyrazol-1-yl)-1,3,5-triazine (Dpbt) were synthesized and incorporated in poly(methyl methacrylate). Their absorption spectra were measured and analyzed using Judd–Ofelt theory. Near-infrared luminescent spectra were studied and the radiative properties have been stimulated. Laser parameters such as effective bandwidths (Δλ_eff), stimulated emission cross-sections (σ_e), and gain bandwidth (σ_g) had also been calculated and compared with other systems. The effect on the fluorescence branching ratio (β) in the ⁴F_3/2→⁴I_11/2 transition of different synergistic ligands had been investigated and the relation between β and Judd–Ofelt parameter Ω₂, Ω₄, Ω₆ was discussed. In conclusion, among the five neodymium complexes, Nd(TTA)₃Dpbt has the largest Ω₂ parameter (33.72 × 10^? 20 cm²), stimulated emission cross-sections, which is found promising to be a candidate for laser materials in further application.     

Spectroscopic properties of Tm3+ doped TeO2-R2O-La2O3 glasses for 1.47 μm optical amplifiers

Upon excitation at 808 nm laser diode, an intense 1.47 μm infrared fluorescence has been observed with a broad full width at half maximum (FWHM) of about 124 nm for the Tm³⁺-doped TeO₂-K₂O-La₂O₃ glass. The Judd–Ofelt parameters found for this glass are: Ω₂ = 5.26 × 10^?20 cm², Ω₄ = 1.57 × 10^?20 cm² and Ω₆ = 1.44 × 10^?20 cm². The calculated emission cross-sections of the 1.47 μm transition are 3.57 × 10^?21 cm², respectively. It is noted that the gain bandwidth, σ_e × FWHM, of the glass is about 440 × 10^?28 cm³, which is significantly higher than that in ZBLAN and Gallate glasses, a high gain of 35.5 dB at 1470 nm can be obtained in a TKL glass fiber. TeO₂-R₂O (R = Li, Na, K)-La₂O₃ glasses has been considered to be more useful as a host for broadband optical fiber amplifier.     

Optical Parameters of Nd‐Doped Gadolinium Aluminium Tetraborate Crystals

Nd‐doped gadolinium aluminium tetraborate, Nd_xGd_1‐xAl₃(BO₃)₄ (NGAB), crystallizes with x = 0.1 in the trigonal system with point group 32, conforming space group R32. They were grown using flux method, of large sizes and good optical quality. The unit cell constants were a = 0.93057 (6) and c = 0.72481 (3) nm, and z = 1. The measured absorption of the NGAB is compared to Judd‐Ofelt (JO) theory. When applied, the JO theory of parity‐forbidden electric‐dipole transitions of rare earth ions on noncentrosymmetric sites demonstrates good agreement. A measured band gap of the eigentransition was about 4.00 eV. The fitted intensity parameters Ot (t = 2, 4, and 6) were 2.446 × 10^‐20, 2.266 × 10^‐20 and 2.598 × 10^‐20 cm². Both the emission properties of the sub‐stable ⁴F_3/2 state with the level lifetime of 506.20 μs and a fluorescence spectrum corresponding to the transition ⁴F_3/2 → ⁴I_11/2 were studied. The results indicate the pass band of laser for potential applications in practice.     

Thermal and Nonlinear Optical Properties of Ca4YO(BO3)3

Ca₄YO(BO₃)₃ (YCOB) crystals have been grown using the vertical Bridgman method. The thermal properties of YCOB were measured for the first time to our knowledge. The specific heat is 729.7 J/kg K at 373K. The average thermal expansion coefficients along the a, b and c axes are 9.9 × 10^‐6 /K, 8.2 × 10^‐6 /K and 12.8 × 10^‐6 /K, respectively, in the temperature range of 293‐1173 K. The thermal conductivities along the a, b and c axes are 1.83 W/mK, 1.72 W/mK and 2.17 W/mK at 373 K. The anisotropy in the measured thermal conductivities of YCOB is consistent with the experimental results of the thermal expansion. The SHG of a Nd: YAG laser was compared with that of a KDP crystal. The effective nonlinear coefficients (d_eff) of YCOB in type I phase matching directions of (θ, ϕ) = (66.3°, 143.5°) and (65.9°, 36.5°) were estimated to be 1.45 pm/V and 0.91 pm/V, respectively. The bulk damage threshold was observed as 85 GW/cm² for single pulse of a Nd:YAG laser with 10 ns pulseduration.     

Emissions of 1.20 and 1.38 μm from Ho3+-doped lithium–barium–bismuth–lead oxide glass for optical amplifications

Efficient infrared emissions at 1.20 μm [⁵I₆ → ⁵I₈ transition] and 1.38 μm [(⁵ F₄, ⁵ S₂) → ⁵I₅ transition] from Ho³⁺-doped lithium–barium–bismuth–lead (LBBP) glass were observed. The stimulated emission cross-sections were calculated to be 0.29 × 10^?20 and 0.25 × 10^?20 cm² for 1.20 and 1.38 μm emissions, respectively. Judd-Ofelt characteristic parameters Ω₂, Ω₄ and Ω₆ for Ho³⁺ in LBBP glass were calculated to be 6.72 × 10^?20, 2.35 × 10^?20 and 0.61 × 10^?20 cm², respectively, which indicates a strong asymmetry and a covalent environment between the Ho³⁺ ions and the ligands in this glass. The optical amplifications operating at these relatively unexplored wavelength regions were evaluated and discussed.     

Optical and laser properties of Nd:LuVO4 crystal

Polarized absorption spectra of Nd:LuVO₄ crystal were measured at room temperature. The optical parameters of π polarization and σ polarization were calculated by Judd‐Ofelt theory. Meanwhile, the phenomenological intensity parameters: Ω₂, Ω₄, and Ω₆ were obtained, then the parameters were used to calculate the luminescence parameters of Nd:LuVO₄ crystal, including oscillator strengths, fluorescence branching ratio, radiative lifetime and integrated emission cross‐sections. Experiments of a‐cut and c‐cut Nd:LuVO₄ lasers were also performed, and opt‐opt conversion efficiency and slope efficiency were 40.3%, 50.5% for a‐cut and 23.6%, 30.9% for c‐cut, respectively. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Growth and spectral properties of Er:Gd2SiO5 crystal

Er³⁺-doped Gd₂SiO₅ (Er:GSO) single crystal with dimensions of ? 35×40 mm³ has been grown by the Czochralski method. The absorption and fluorescence spectra of the Er:GSO crystal were measured at room temperature. The spectral parameters were calculated based on Judd–Ofelt theory, and the intensity parameters Ω₂, Ω₄ and Ω₆ are obtained to be 6.168×10^?20, 1.878×10^?20, and 1.255×10^?20 cm², respectively. The emission cross-section has been calculated by Fuechtbauer–Ladenbury formula.     

Optical properties of erbium-doped fluorochlorozirconate glasses

We report the optical properties of a fluorochlorozirconate (FCZ) glass with the composition 53% ZrF₄, 20% NaF, 3.5% AlF₃, 3% LaF₃, 0.5% InF₃, (20 ? x)% BaCl₂, x% BaF₂ with x varying from 0% to 2%, and doped with various amounts of trivalent erbium by the addition of ErCl₃. Annealing of the as-prepared glass in inert (N₂) or reducing (5%H₂ + 95%Ar) atmospheres at temperatures that ensure the conversion of the glass into a glass-ceramic by the nucleation of BaCl₂ nanocrystals, does not significantly change any of Er³⁺ related absorption and photoluminescence (PL) characteristics. We have carried out a Judd–Ofelt analysis of the absorption spectra and obtained Ω₂ = (1.92 ± 0.3) × 10^? 20 cm², Ω₄ = (0.88 ± 0.16) × 10^? 20 cm² and Ω₆ = (0.59 ± 0.08) × 10^? 20 cm², and also the radiative lifetimes of the ⁴I_13/2→⁴I_15/2, ⁴I_11/2→⁴I_15/2 and ⁴S_3/2→⁴I_15/2 bands. The radiative lifetime from the Judd–Ofelt analysis for the ⁴I_13/2→⁴I_15/2 band is in good agreement with the experimentally measured PL decay time. The examination of the optical properties of powdered samples with different average particle size does not show any photon trapping effects. We have determined the spectral absorption and emission cross-sections and then estimated the possible spectral optical gain for varying degrees of relative populations of the ⁴I_13/2 and ⁴I_15/2 manifolds.     

Study of the surface state density and potential in MIS diode Schottky using the surface photovoltage method

ABSTRACT

The effects of surface preparation and illumination on electric parameters of Au/GaN/GaAs Schottky diode were investigated. The thin GaN film is realized by nitridation of GaAs substrates with different thicknesses of GaN layers (0.7 – 2.2 nm). In order to study the electrical characteristics under illumination, we use an He-Ne laser of 632 nm wavelength. The I(V) current- voltage, the surface photovltage SPV measurement were plotted and analysed taking into consideration the influence of charge exchange between a continuum of the surface states and the semiconductor. The barrier height Ф_Bn, the serial resistance R_s and the ideality factor n are respectively equal to 0.66 eV, 1980 Ω, 2.75 under dark and to 0.65 eV, 1160 Ω, 2.74 under illumination for simple 1 (GaN theckness of 0.7 nm). The interface states density N_ss in the gap and the excess of concentration δn are determined by fitting the experimental curves of the surface photovltage SPV with the theoretical ones and are equal to 4.5×10¹² eV^?1 cm^?2, 5×10⁷ cm^?3, respectively, for sample 1 and 3.5×10¹² eV^?1 cm^?2, 7×10⁸ cm^?3 for sample 2 (GaN theckness of 2 nm). The results confirm that the surface photovoltage is an efficient method for optical and electrical characterizations.     

Spectroscopic properties and energy transfer in Yb3+–Ho3+ co-doped germanate glass emitting at 2.0 μm

A new kind of germanate glass co-doped with Yb³⁺–Ho3⁺ was prepared. The J-O parameters were calculated to be Ω₂ = (6.59 ± 0.21) × 10^? 20 cm², Ω₄ = (2.77 ± 0.36) × 10^? 20 cm², and Ω₆ = (1.90 ± 0.25) × 10^? 20 cm². The little overlap between the absorption cross section and stimulated emission cross section indicates a non-resonant energy transfer process. The calculation demonstrates that the energy transfer between Yb³⁺ and Ho³⁺ is one-phonon assisted in a great measure. The gain coefficient of Ho³⁺ at 2.0 μm was also calculated. The fluorescence measurement shows the Yb³⁺ co-doping enhances the 2.0 μm emission remarkably.     

Thermal properties of a Nd:LuVO4 crystal

A Nd‐doped lutetium orthovanadate Nd:LuVO₄ crystal has been grown using a modified Czochralski method. The thermal properties of this crystal have been studied by measuring the thermal expansion, specific heat and thermal diffusivity. The thermal expansion coefficients are α₁₁ = 1.7 × 10^‐6, α₂₂ = 1.5 × 10^‐6 and α₃₃ = 9.1 × 10^‐6/K in the temperature range of 298–573 K along the three respective crystallographic axes. The specific heat is almost linear and increases from 0.442 to 0.498 Jg^‐1K^‐1 in the measured temperature range. The thermal diffusivity is anisotropic and decreases with increasing temperature from 295 to 548 K. At room temperature the calculated thermal conductivities κ₁₁ and κ₃₃ are 7.96 and 9.77 Wm^‐1K^‐1, respectively. These thermal parameters of Nd:LuVO₄ crystal have indicated that it is an excellent candidate laser material. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Electric Characterization of Indium Sesquiselenide Single Crystals

Conductivity, Hall-effect measurements were performed on δ-phase In₂Se₃ single crystals, grown by the Bridgman method over the temperature range 150–428 K, in the directions perpendicular and parallel to the c-axis. The anisotropy of the electrical conductivity and of the Hall coefficient of n-type In₂Se₃ had been investigated. The values of the Hall coefficient and electrical conductivity at room temperature spreads from an order of R_H11 = 1.36 × 10⁴ cm³/coul, σ₁₁ = 4.138 × 10⁻³ Ω⁻¹ cm⁻¹ and R_H = 66.55 × 10⁴ cm³/coul, σ = 0.799 × 10⁻³ Ω⁻¹ cm⁻¹ for parallel and perpendicular to c-axis, respectively. The temperature dependence of Hall mobility and carrier concentration are also studied.     

The growth of high-quality MCT films by MBE using in-situ ellipsometry

The ellipsometry and RHEED study of high-quality MCT films grown on (112)- and (130) CdTe and GaAs by MBE was carried out. The dependence of the ellipsometric parameter ψ on MCT composition is evaluated. It was shown that such parameters as growth rate, the surface roughness, initial substrate temperature, and film composition may be measured by the in-situ ellipsometry. The appearance of surface roughness was observed in the initial stage of MCT growth under various compositions (x_CdTe = 0 ÷ 0.4). The further growth at optimum conditions leads to the smoothing of the surface and supplies us with high-quality MCT films. The concentration, mobility, and life time of carriers in MCT films were respectively: n = 1.8 × 10¹⁴ ÷ 8.2 × 10¹⁵ cm⁻³, μ_n = 44000 ÷ 370000 cm² V⁻¹ s⁻¹, τ_n = 40 ÷ 220 ns; p = 1.8 × 10¹⁵ ÷ 8.4 × 10¹⁵ cm⁻³, μ_p = 215 ÷ 284 cm² V⁻¹ s⁻¹, τ_p = 12 ÷ 20 ns.     

Physicochemical properties of the organometallic nonlinear optical crystal: MnHg(SCN)4(C3H8O2)

The growth morphology of MMTG (manganese mercury thiocyanate glycol monomethyl ether, MnHg(SCN)₄(C₃H₈O₂)) crystal was indexed according to the X‐ray powder diffraction spectroscopy. The density and Mohs hardness were determined at room temperature. The specific heat of the crystal is 458.6 J.mol^‐1K^‐1 at 300 K. The thermal expansion coefficient (TEC) along the a, b and c axis is a₁=6.89 × 10^‐5 K^‐1, a₂=6.78 × 10^‐5 K^‐1 and a₃=2.08 × 10^‐5 K^‐1, respectively. The sameness and difference of the TECs are interpreted on the basis of crystal structure. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

The structure of 2R-(3′S-benzyloxy-5′S-hydroxy-2′R-hydroxymethyl-1′-oxacyclohexan-6′S-yl)-propionic acid-1,5′-lactone,C16H20O5

The title compound is C₁₆H₂₀O₅, MW=292.3, orthorhombic,P2₁2₁2₁,a=9.741(2),b=29.391(7),c=5.354(1) Å from diffractometer measurements,V=1532.8 ų,Z=4,D _c =1.267 g cm^?3,D _o =1.271 g cm^?3 (ether/1,1,2,2-tetrabromoethane), λ(Mo Kα)=0.71069 Å,F(000)=624,μ=1.02 cm^?1, crystal dimensions 0.23×0.23×0.40 mm,R=0.049 for 1164 observed reflections. The molecule contains a possibly significant asymmetric ether linkage between the oxacyclohexane ring and the highly anisotropic benzyl ring. The packing consists of zigzagged chains parallel to thea-axis formed by hydrogen bonds. The chains are separated by van der Waals contacts.     

Growth and characterization of KBi(WO4)2 single crystals

Potassium bismuth tungstate [KBi(WO₄)₂] single crystals with dimensions up to 20 mm × 15 mm × 15 mm have been successfully grown by using the top‐seeded solution growth technique and K₂W₂O₇ as solvent. Experiments show that this crystal is unstable in a strong acid or alkali environment and has a blue fluorescence emission. The density, hardness, melting point, absorption edge, transparency range, prominent Raman shift frequency are 7.57 g/cm³, 238 kg/mm², 800 °C, 380 nm, 400–5450 nm, 868 cm^–1 respectively. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)