Growth and spectral properties of Nd:GdVO4 laser crystal

In this paper, the Czochralski growth, absorption spectra, and photoluminescence spectra of Nd:GdVO₄ crystals are studied. From its absorption spectra, Nd:GdVO₄ is found to exhibit an anisotropic optical absorption effect, and its effective Judd-Ofelt parameters are calculated: Ω₂=10.281×10⁻²⁰ cm², Ω₄=5.426×10⁻²⁰ cm² and Ω₆=9.943×10⁻²⁰ cm². By these parameters, the absorption oscillator strengths, emission oscillator strengths, transition probabilities, fluorescence branch ratios, energy lifetimes, and integrated emission cross-sections are also derived. The photoluminescence spectra of Nd:GdVO₄ crystal consist of a wide emission band of host and the characteristic emission bands of Nd³⁺. Based on the excitation spectrum, both the two evident peaks locating at 345 and 371 nm are ascribed to the characteristic excitation of Nd³⁺, and an energy transfer from the host to its doping Nd³⁺ ions is indicated.     

Growth and spectroscopic characterization of Er: Sr3Y(BO3)3 crystal

This paper reports the growth and spectroscopic characterization of Er³⁺:Sr₃Y(BO₃)₃ crystal. Er³⁺:Sr₃Y(BO₃)₃ crystal with dimensions up to ∅20×35 mm³ has been grown by Czochralski method. The polarized spectroscopic properties of Er³⁺:Sr₃Y(BO₃)₃ crystal were investigated. Based on the Judd-Ofelt theory, the effective intensity parameters Ω_t were obtained: Ω₂=1.71×10⁻²⁰ cm², Ω₄=1.39×10⁻²⁰ cm², Ω₆=0.74×10⁻²⁰ cm² for π-polarization, and Ω₂=1.77×10⁻²⁰ cm², Ω₄=1.44×10⁻²⁰ cm², Ω₆=0.65×10⁻²⁰ cm² for σ-polarization. The emission cross-section σ_em was calculated to be 4.75×10⁻²¹ cm² for π-polarization at 1536 nm and 6.30×10⁻²¹ cm² for σ-polarization at 1537 nm. The investigated results showed that Er³⁺:Sr₃Y(BO₃)₃ crystal may be regarded as a potential laser host material for 1.55 μm IR solid-state lasers.     

Spectral properties of Nd:Ca2Nb2O7 crystal

This paper reports the spectral properties of Nd³⁺:Ca₂Nb₂O₇. The spectral parameters of Nd³⁺ in Nd³⁺:Ca₂Nb₂O₇ crystal have been investigated based on Judd-Ofelt theory. The spectral parameters were obtained. The parameters of line strengths Ω_λ are Ω₂=4.967×10⁻²⁰ cm², Ω₄=5.431×10⁻²⁰ cm², Ω₆=5.693×10⁻²⁰ cm². The radiative lifetime, the fluorescence lifetime and the quantum efficiency are 122 μs, 103 μs and 84.4%, respectively. The fluorescence branch ratios calculated: β₁=0.425, β₂=0.479, β₃=0.091, β₄=0.004. The emission cross section at 1068 nm is 6.204×10⁻²⁰ cm².     

Spectra and intensity parameters of Tm ion in YAlO3 crystal

High quality Tm-doped YAlO₃ (Tm:YAlO₃) single crystals were obtained along crystallographic b-axis by the Czochralski technique. Optical absorption and fluorescence spectra for Tm³⁺ in YAlO₃ crystals were investigated at room temperature. Based on Judd-Ofelt approach, the intensity parameters Ω_t (t = 2, 4, 6) of Tm:YAlO₃ were calculated to be Ω₂ = 0.93 × 10⁻²⁰  cm², Ω₄ = 2.23 × 10⁻²⁰ cm², and Ω₆ = 1.12 × 10⁻²⁰ cm². The spectral parameters such as experimental and theoretical oscillator strengths, radiative transition probabilities, radiative lifetime and the fluorescence branching ratio were also obtained. All results indicate that Tm:YAlO₃ is a potential candidate for compact, efficient mid-infrared lasers with laser diode pumping.     

Characterization of Y2O3 gate dielectric on n-GaAs substrates

Physical and electrical properties of sputtered deposited Y₂O₃ films on NH₄OH treated n-GaAs substrate are investigated. The as-deposited films and interfacial layer formation have been analyzed by using X-ray photoelectron spectroscopy (XPS) and secondary ion mass spectroscopy (SIMS). It is found that directly deposited Y₂O₃ on n-GaAs exhibits excellent electrical properties with low frequency dispersion (<5%), hysteresis voltage (0.24 V), and interface trap density (3 × 10¹² eV⁻¹ cm⁻²). The results show that the deposition of Y₂O₃ on n-GaAs can be an effective way to improve the interface quality by the suppression on native oxides formation, especially arsenic oxide which causes Fermi level pinning at high-k/GaAs interface. The Al/Y₂O₃/n-GaAs stack with an equivalent oxide thickness (EOT) of 2.1 nm shows a leakage current density of 3.6 × 10⁻⁶ A cm⁻² at a V_FB of 1 V. While the low-field leakage current conduction mechanism has been found to be dominated by the Schottky emission, Poole-Frenkel emission takes over at high electric fields. The energy band alignment of Y₂O₃ films on n-GaAs substrate is extracted from detailed XPS measurements. The valence and conduction band offsets at Y₂O₃/n-GaAs interfaces are found to be 2.14 and 2.21 eV, respectively.     

Spectral properties of Nd-doped Sr3Ga2Ge4O14 crystal

Neodymium doped strontium gallogermanate crystals were grown successfully by the Bridgman technique. The linear thermal expansion coefficients for the c- and a-axes were measured as 5.8 × 10⁻⁶ °C⁻¹ and 6.5 × 10⁻⁶ °C⁻¹. Absorption spectra, and fluorescence spectra, as well as fluorescence decay curves of Nd³⁺-doped Sr₃Ga₂Ge₄O₁₄ crystal, have been recorded at room temperature and used to calculate the absorption and stimulated emission cross-sections. Based on the Judd-Ofelt theory, three intensity parameters were obtained. The luminescent quantum efficiency of the ⁴F_3/2 level was determined to be approximately 73.8% for this material. Compared with other Nd³⁺-doped laser crystals, Nd³⁺-doped Sr₃Ga₂Ge₄O₁₄ crystal displays special laser properties due to its disorder structure.     

Energy transfer and upconversion of Nd doped RbY2Cl7

Single crystals of Nd³⁺:RbY₂Cl₇ were grown by the Bridgman-Stockbarger method. The host crystal contains two slightly inequivalent Y³⁺ ions, each with an approximate C_2v site symmetry. Anti-Stokes emission from the ⁴G_7/2 and ⁴D_3/2 levels was observed after laser excitation of the ⁴F_3/2 and ⁴F_9/2 multiplets. Laser excitation at 413 cm⁻¹ or 453 cm⁻¹ above the ⁴F_3/2 multiplet resulted in emission from the ²P_1/2 level. Laser site-selective upconverted emission spectra have been measured, as well as their emission transients and power dependence. Possible excited state absorption and energy-transfer upconversion (ETU) mechanisms are proposed and discussed. Due to the smaller crystal field and a somewhat different energy level structure for the Nd³⁺ ions in RbY₂Cl₇ as compared with those observed for Nd³⁺ in fluoride or oxide hosts, the ⁴G_7/2 and ⁴D_3/2 multiplets are populated under ⁴F_3/2 excitation in a three and four step ETU process, respectively, instead of in a two and three step process as observed for the lighter hosts.     

Spectroscopic analysis of Er transition in Mg/Er-codoped LiNbO3 crystal

We present a Judd-Ofelt spectroscopic analysis on the Mg/Er-codoped congruent lithium niobate (LiNbO₃) crystals. The Judd-Ofelt model is applied to the room temperature unpolarized absorption intensities of Er³⁺ ions on eleven transition bands to determine their intensity parameters: Ω₂=2.36×10⁻²⁰ cm², Ω₄=0.76×10⁻²⁰ cm², Ω₆=0.30×10⁻²⁰ cm² in Er:LiNbO₃ crystal heavily codoped with MgO. The radiative lifetime of ²H_9/2 becomes longer when MgO is added into Er:LiNbO₃ crystal. The experimental lifetimes are obtained using microsecond time-resolved spectra at 400 nm femtosecond pulse excitation to predict radiative quantum efficiency. Combining higher radiative quantum efficiency with longer radiative lifetime, we conclude that Mg/Er-codoped LiNbO₃ crystals are more suitable than Er: LiNbO₃ ones in laser materials.     

Spectroscopic and photoluminescence properties of Ho doped Ba0.65Sr0.35TiO3 nanocrystals

Ho³⁺ doped Ba_0.65Sr_0.35TiO₃ (BST) nanocrystals was prepared by sol-gel method. The structural and morphological properties of the nanocrystals were characterized using X-ray diffraction (XRD) and transmission electron microscopy (TEM). The absorption spectrum, photoluminescence spectrum and fluorescence time decay curve were measured at room temperature. Based on the Judd-Ofelt (J-O) theory, the J-O intensity parameters Ω_t (t=2, 4, 6) of Ho³⁺ doped BST nanocrystals were calculated to be 0.67×10⁻²⁰ cm², 1.11×10⁻²⁰ cm² and 1.09×10⁻²⁰ cm², respectively. The emission probabilities, radiative lifetimes and branching ratios of the different Ho³⁺ transitions were also determined. The emission cross sections of the important intermanifold transitions ⁵F₄,⁵S₂→⁵I₈, ⁵F₅→⁵I₈ and ⁵F₄→⁵I₇ have been calculated from the luminescence spectrum. The room temperature fluorescence lifetime of the ⁵S₂→⁵I₈ transition for Ho³⁺ in BST nanocrystals was measured and the radiative quantum efficiency was estimated to be 61.9%.     

Spectroscopy of Ca3(BO3)2: Dy crystal

Dy³⁺: Ca₃(BO₃)₂ crystal was grown successfully by the Czochraski technique. The absorption spectrum was measured and its absorption peaks were assigned. The Judd-Ofelt intensity parameters were found to be Ω₂=5.216×10⁻²⁰, Ω₄=1.858×10⁻²⁰, Ω₆=0.623×10⁻²⁰ cm². The spectroscopic parameters of this crystal such as the oscillator strengths, radiative transition probabilities, radiative lifetime as well as the branching ratios were calculated. Also, room temperature luminescence decay curve in correspondence with the emission line ⁴F_9/2→⁶H_13/2 centered at 575 nm was measured.     

Investigation of spectroscopic properties and thermal stability of Er/Yb-co-doped Bi2O3-B2O3-Ga2O3 glasses

A series of Er³⁺/Yb³⁺-co-doped 60Bi₂O₃-(40−x) B₂O₃ -xGa₂O₃ (BBGA x=0, 4, 8, 12, 16 mol%) glasses have been prepared. The absorption spectra, emission spectra, fluorescence lifetime of Er³⁺:⁴I_13/2 level and thermal stability were measured and investigated. Three Judd-Ofelt intensity parameters Ω_t (t=2,4,6) (Ω₂=(4.67-5.93)×10⁻²⁰ cm², Ω₄=(1.50-1.81)×10⁻²⁰ cm², Ω₆=(0.92-1.17)×10⁻²⁰ cm²) of Er³⁺ ions were calculated by Judd-Ofelt theory. It is found that the Ω₆ first increases with the increase of Ga₂O₃ content from 0 to 8 mol% and then decreases, which is mainly affected by the number of non-bridging oxygen ions of the glass network. The high peak of stimulated emission cross-section () of Er³⁺: ⁴I_13/2→⁴I_15/2 transition were obtained according to McCumber theory and broad full width at half maximum (FWHM=69-76 nm) of the ⁴I_13/2→⁴I_15/2 transition of Er³⁺ ions were measured. The results indicate that these new BBGA glasses can be used as a candidate host material for potential broadband optical amplifiers.     

Crystal field energy levels of the laser crystal Gd3Ga5O12: Nd

The crystal field energy levels of laser crystal Gd₃Ga₅O₁₂: Nd³⁺ are calculated using the diagonalization (of energy matrix) method. From the calculations, the 93 observed crystal field energy levels are explained reasonably and the root-mean-square (r.m.s.) deviation σ(≈25.6 cm⁻¹) and the scalar crystal-field strength parameter Nv (≈3847 cm⁻¹) are obtained. The results are discussed.     

Optical absorption and emission properties of Nd in TeO2-WO3 and TeO2-WO3-CdO glasses

Effects of WO₃ and CdO on the spectroscopic properties of Nd³⁺ doped tellurite glasses were investigated. The optical band gaps and Urbach energies of the samples were determined using the dependence of the absorption coefficient on the photon energy. The Urbach energies were found to vary from 0.18 to 0.25 eV as the WO₃ content in the binary glasses decreased from 20.0 to 10.0 mol% while the optical band gap of the same glasses did not show an appreciable dependence on the glass composition. Judd-Ofelt (Ω_t) parameters were calculated from the optical absorption spectra measured at room temperature. In all the glasses the J-O parameters follow the same trend as Ω₂>Ω₆>Ω₄. The J-O intensity parameters were used to compute the radiative properties such as the radiative transition probabilities (A_ed), branching ratios (β) and radiative lifetimes (τ_r) for all the possible fluorescence bands. The fluorescence spectra obtained upon 805.2 nm excitation exhibited an intense emission band centered at 1064 nm (⁴F_3/2→⁴I_11/2) and two weak bands at 910 nm (⁴F_3/2→⁴I_9/2), and 1340 nm (⁴F_3/2→⁴I_13/2). The stimulated emission cross-section for the 1064 nm emission was determined using the emission spectra. The highest gain bandwidth (σ_e×Δλ_P) was determined to be 155.4 for the 0.79TeO₂-0.15WO₃-0.05CdO ternary glass composition, which could be more useful as promising material for the design and development of fiber amplifiers and lasers.     

Preparation, characterization and properties of N-rich Zr-N thin film with Th3P4 structure

A N-rich Zr-N film with Th₃P₄ structure (denoted as c-Zr₃N₄) was grown on Si and glass substrate by radio frequency (rf) magnetron sputtering technique with high pure Zr as target and high pure N₂ as sputtering gas. The crystal structure and composition of the c-Zr₃N₄ was characterized by X-ray diffractometry, transmission electron microscopy and X-ray photoelectron spectroscopy. The lattice constant of the c-Zr₃N₄ was measured to be about 0.674 nm. Hall measurement indicates that the c-Zr₃N₄ compound is a p-type semiconductor with resistivity of 2.121 × 10⁴ Ω cm, carrier concentration of 9 × 10¹⁴ cm⁻³ and Hall mobility of 0.34 cm²/(V s). Its bandgap was evaluated by absorption spectroscopy to be about 2.8 eV. A mechanism of formation of the c-Zr₃N₄ compound was suggested in the present work.     

Optical properties of Er/Yb-codoped transparent PLZT ceramic

Optical absorption and emission spectra of Er³⁺/Yb³⁺ ions in PLZT (Pb_1−xLa_xZr_yTi_1−yO₃) ceramic have been studied. Based on the Judd—Ofelt (J-O) theory, the J-O intensity parameters were calculated to be Ω₂=2.021×10⁻²⁰ cm², Ω₄=0.423×10⁻²⁰ cm², Ω₆=0.051×10⁻²⁰ cm² from the absorption spectrum of Er³⁺/Yb³⁺-codoped PLZT. The J-O intensity parameters have been used to calculate the radiative lifetimes and the branching ratios for some excited ⁴I_13/2, ⁴I_11/2, ⁴I_9/2⁴F_9/2, and ⁴S_3/2 levels of Er³⁺ ion. The stimulated emission cross-section (8.24×10⁻²¹ cm²) was evaluated for the ⁴I_13/2→⁴I_15/2 transition of Er³⁺. The upconversion emissions at 538, 564, and 666 nm have been observed in Er³⁺/Yb³⁺-codoped PLZT by exciting at 980 nm, and their origins were identified and analyzed.     

Collision induced absorption spectra of the fundamental band of D2 in binary mixtures D2-Kr at 298 K

The enhancement spectrum of the collision induced absorption of D₂ in its fundamental band region 2600-4000 cm⁻¹ in binary mixtures D₂-Kr was studied at 298 K for base densities of D₂ in the range 9-20 amagat and for partial densities of Kr in the range 7-120 amagat. The binary absorption coefficient of the band has been determined from the measured integrated absorption coefficient and found to be 3.9 × 10⁻³ cm⁻² amagat⁻². An analysis of the experimental spectrum was carried out by assuming appropriate line-shape functions and the half-width parameters δ₁, δ₂, δ_d and δ_c of the long range quadrupole, and of the short range overlap induced transitions have been determined. Good agreement was obtained between the recorded spectrum of the fundamental band and the synthetic profile.     

The ν1 + 3ν2 + 3ν3 and 4ν1 + ν2 + ν3 bands of ozone by CW-cavity ring down spectroscopy between 5900 and 5960 cm

The absorption spectrum of ozone, ¹⁶O₃, has been recorded in the 5903-5960 cm⁻¹ region by high sensitivity CW-cavity ring down spectroscopy (α_min ∼ 5 × 10⁻¹⁰ cm⁻¹). The ν₁ + 3ν₂ + 3ν₃ and 4ν₁ + ν₂ + ν₃ A-type bands centred at 5919.15 and 5947.07 cm⁻¹ were newly observed. A set of 173 and 168 energy levels could be experimentally determined for the (1 3 3) and (4 1 1) states, respectively. Except for a few K_a = 5 levels of the (4 1 1) state, the rotational structure of the two states was found mostly unperturbed. The spectroscopic parameters were determined from a fit of the corresponding line positions by considering the (1 3 3) and (4 1 1) states as isolated. The determined effective Hamiltonian and transition moment operators were used to generate a list of 785 transitions given as Supplementary Material.     

Theoretical study on the kinetics for OH reactions with CH3OH and C2H5OH

Kinetics and mechanisms for reactions of OH with methanol and ethanol have been investigated at the CCSD(T)/6-311 + G(3df, 2p)//MP2/6-311 + G(3df, 2p) level of theory. The total and individual rate constants, and product branching ratios for the reactions have been computed in the temperature range 200-3000 K with variational transition state theory by including the effects of multiple reflections above the wells of their pre-reaction complexes, quantum-mechanical tunneling and hindered internal rotations. The predicted results can be represented by the expressions k₁ = 4.65 × 10⁻²⁰ × T^2.68 exp(414/T) and k₂ = 9.11 × 10⁻²⁰ × T^2.58 exp(748/T) cm³ molecule⁻¹ s⁻¹ for the CH₃OH and C₂H₅OH reactions, respectively. These results are in reasonable agreements with available experimental data except that of OH + C₂H₅OH in the high temperature range. The former reaction produces 96-89% of the H₂O + CH₂OH products, whereas the latter process produces 98-70% of H₂O + CH₃CHOH and 2-21% of the H₂O + CH₂CH₂OH products in the temperature range computed (200-3000 K).     

Intense ultraviolet and blue upconversion emissions in Yb-Tm codoped stoichiometric Y7O6F9 powder

Stoichiometric Y₇O₆F₉ powder codoped with Yb³⁺-Tm³⁺ was synthesized via co-precipitation and subsequent calcining route. The results of X-ray diffraction and transmission electron microscopy reveal that when the calcining temperature is beyond 800 °C, orthorhombic YF₃ nanoparticles can be completely oxidized into orthorhombic Y₇O₆F₉ powder. Under the excitation of a 980 nm laser, Y₇O₆F₉ powder exhibits multicolor UC emission in regions spanning the UV to the NIR. In addition, the upconversion emission intensities of YF₃, Y₇O₆F₉ and Y₂O₃ powders were compared under the same dopant condition (Yb/Tm=5/0.5 mol%). The low phonon energy revealed by Raman spectra helped to understand the high efficient upconversion emission of Y₇O₆F₉ and the main phonon vibration of Y₇O₆F₉ lies at 472 cm⁻¹, which is far lower that of Y₂O₃ (at 708 cm⁻¹). Our results indicate that orthorhombic rare earth ions doped Y₇O₆F₉ is an efficient matrix for UV and blue UC emission, and has potential applications in color displays, anti-counterfeiting and multicolor fluorescent labels.     

Fluorescence and Judd-Ofelt analysis of Nd ions in oxyfluoride glass ceramics containing CaF2 nanocrystals

Judd-Ofelt analyses of Nd³⁺ ions in the oxyfluoride glasses and glass ceramics containing CaF₂ nanocrystals are performed to evaluate the intensity parameters Ω_2,4,6, spontaneous emission probability, radiative lifetime, quantum efficiency, as well as stimulated emission cross-section. The influences of Nd³⁺-doping level and heating temperature on these parameters for the ⁴F_3/2→⁴I_J (J=9/2, 11/2, and 13/2) transitions are systematically discussed. The decrease of intensity parameter Ω₂ evidences the incorporation of Nd³⁺ ions into CaF₂ nanocrystals after crystallization. With increasing of Nd³⁺-doping level, the measured lifetime and quantum efficiency gradually decrease, while the stimulated emission cross-section keeps almost unchanged. For 1.0 mol% Nd³⁺-doped sample, both the emission intensity and the measured lifetime enhance with increasing of heating temperature up to 650 °C. The results indicate that the investigated glass ceramics are potentially applicable as the 1.06 um laser host.