A comparison of selected organic tracers for quantitative scalar imaging in the gas phase via laser-induced fluorescence

Single crystal of La₃Ga_5.5Ta_0.5O₁₄ (LGT) containing intentionally 0.5 % of Ho³⁺ and 1 % of Yb³⁺ was grown by the Czochralski method. Examination of chemical composition of the grown crystal revealed that luminescent holmium and ytterbium ions are preferably retained in the melt and their actual concentrations are 0.12 and 0.24 %, respectively. Spectroscopic investigation performed encompassed IR host absorption spectra and Raman spectra at room temperature, optical absorption and luminescence spectra of Ho³⁺ and Yb³⁺ at room temperature and at 5 K, and luminescence decay curves at room temperature. It was found that all spectral bands recorded show important inhomogeneous line broadening. This feature was attributed to structural disorder inherent to the crystal lattice in which pentavalent Ta⁵⁺ ions occupy octahedral Ga(1) sites together with trivalent Ga³⁺ ions. Despite small concentrations of luminescent ions, the occurrence of nonradiative interaction that feeds the ⁵I₆ and ⁵I₇ levels of Ho³⁺ ions by transfer of an excitation from the ²F_5/2 level of Yb³⁺ ions was evidenced. Based on examination of spectroscopic parameters evaluated, it was concluded that LGT:Ho, Yb may be considered as a potential intermediate-gain laser active material able to emit infrared radiation from the ⁵I₇ → ⁵I₈ transition of Ho³⁺ around 2 micrometres upon laser-diode pumping into Yb³⁺ absorption band.     

A new method for measuring electro-optical coefficients of the optically active crystals

A new method has been proposed to measure the electro-optical coefficients of the crystals which have optical activity. By using this method, the half-wave voltage and the electro-optical coefficients of the optically active crystals La₃Ga₅SiO₁₄ (LGS), La₃Ga_5..5Nb_0.5O₁₄ (LGN), La₃Ga_5.5Ta_0.5Si₁₄ (LGT) have been determined. The resultants obtained are: γ₁₁(LGS)=1.9 pm/V, γ₁₁(LGN)=0.75 pm/V, γ₁₁(LGT)=0.57 pm/V. This method can also be used to simulate the on–off state of the electro-optical Q switch in the laser cavity, whether the switch is made of the ordinary crystals or the optically active crystals.     

Direct growth of graphene film on piezoelectric La3Ga5.5Ta0.5O14 crystal

For the first time, a few layer graphene was grown on the surface of the polar X ‐cut (110) of a piezoelectric La₃Ga_5.5Ta_0.5O₁₄ crystal by the CVD method. This polar X ‐cut is characterized by a good matching of the crystal lattice parameters of La₃Ga_5.5Ta_0.5O₁₄ and two‐dimensional graphene crystal, as well as the presence of piezoelectric fields on the surface of the substrate, which could affect the graphene growth process. Raman spectroscopy investigation has shown the ability for direct growth of graphene on the piezoelectric crystal. The NEXAFS spectroscopy studies of the film grown on the surface of the X ‐cut of an La₃Ga5_.5Ta_0.5O₁₄ crystal also confirmed that the grown film is graphene. Moreover, the NEXAFS spectra enable the conclusion that additional electron states are formed as a result of chemical bonding between the atoms of graphene and the substrate which proceeds through hybridization of the valence electron states of the substrate and graphene atoms. (© 2016 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)     

Spectroscopic analysis of Cr,Er:Gd3Ga5O12 crystals as candidates of potential xenon lamp pumped ~ 2.7 μm laser

A series of Cr,Er:Gd₃Ga₅O₁₂ crystals with high concentrations of Er^3 + were grown by Czochralski method. The absorption spectra, the up-conversion, near infrared (NIR) and mid-infrared (Mid-IR) luminescence spectra as well as the luminescence decay curves of Er: ⁴I_13/2 and ⁴I_11/2 levels were measured at room temperature. The spectroscopic properties of Cr,Er:Gd₃Ga₅O₁₂ crystals and Cr–Er energy transfer processes were investigated. The spectroscopy of the Er^3 +:⁴I_11/2 → ⁴I_13/2 transition was centralized to discuss, and the important optical parameters including luminescence lifetimes and the Cr–Er energy transfer efficiency are presented. Based on the comprehensive spectral analyses, 0.6 at.%Cr/50 at.%Er:GGG crystal is preferred as candidate of potential xenon lamp pumped ~ 2.7 μm laser in this work.     

Infrared-excited bright green and red luminescence in La3Ga5.5Ta0.5O14 doped with erbium and ytterbium

Bright green (at 525 and 550 nm) and red (at 660 nm) luminescence in Er:Yb:La₃Ga_5.5Ta_0.5O₁₄ (LGT) powder synthesized by solid state reaction was obtained by pumping at 936 nm. Yb³⁺-Er³⁺ energy transfer processes accounting for population of the ²H2_11/2, ⁴S_3/2 and ⁴F_9/2 Er³⁺ levels are discussed. The dependence of ratio between the intensities of the green and red luminescence on pump intensity is analyzed. The rather high quantum efficiency (58%) of the (⁴S_3/2, ²H2_11/2) Er³⁺ emitting level recommends LGT doped with erbium and ytterbium for upconversion applications.     

High-temperature stability of the phase composition of langasite family crystals

Thermal stability of the phase composition of langasite family crystals is studied by means of high-temperature X-ray diffractometry upon heating in vacuo and in air. Upon heating above 1000°C in vacuo, the partial decomposition of the initial phase is observed in La₃Ga₅SiO₁₄, La₃Ta_0.5Ga_5.5O₁₄, and Ca₃TaGa₃Si₂O₁₄ crystals; this is accompanied by the emergence of gallium-depleted oxides of the main elements, due to the formation of volatile gallium protoxide and the loss of gallium in the surface layer of the crystals. Langasite family crystals are found to be stable when annealed in air up to a temperature of 1200°C.     

Growth and characterization of Nd:Lu3ScxGa5 − xO12 series laser crystals

A new series Nd:Lu₃Sc_xGa_5 − xO₁₂ (x = 0.5, 0.8, 1, 1.2 and 1.5) laser crystals have been successfully grown by the optical floating zone method. Their absorption and luminescence spectra were measured at room temperature and spectral parameters were systemically calculated using Judd-Ofelt (JO) theory. The fluorescence τ_f lifetimes were experimentally measured and compared with the theoretical results. Diode-pumped continuous-wave (CW) laser performance at 1.06 μm with mixed crystals was demonstrated. The influence of different x values on laser performance and spectral parameters was also discussed. All the results show that Nd:Lu₃Sc_xGa_5 − xO₁₂ series crystals should be suitable for laser application.     

X-ray diffraction analysis of the surface acoustic wave propagation in langatate crystal

X-ray diffraction on a langatate crystal (La₃Ga_5.5Ta_0.5O₁₄, LGT) modulated by a Λ=12 μm Rayleigh surface acoustic wave (SAW) was studied in a double axis X-ray diffractometer scheme at the BESSY synchrotron radiation source. SAW propagation in the crystal causes sinusoidal modulation of the crystal lattice and the appearance of diffraction satellites on the rocking curves, with their number, angular positions, and intensities depending on the wavelength and amplitude of acoustic vibrations of the crystal lattice. Strong absorption of X-ray radiation in LGT enables the observation of the diffraction spectra extinction at certain SAW amplitudes. X-ray diffraction spectra analysis makes it possible to determine SAW amplitudes and wavelengths, to measure the power flow angles, and investigate the diffraction divergence in acoustic beam in LGT.     

Crystal structure and optical activity of La3Nb0.5Ga5.5O14 and Sr3Ga2Ge4O14 single crystals of the langasite family

Precision X-ray structural studies of the La₃Nb_0.5Ga_5.5O₁₄ and Sr₃Ga₂Ge₄O₁₄ single crystals were carried out. The space group P321 was confirmed. The anomalous X-ray scattering was taken into account to establish the absolute structures (chirality) of the crystals; they proved to be of different sign. The structural features responsible for the optical activity of crystals were revealed, and the dependence of the magnitude and sign of specific rotation on the structural parameters of these compounds were determined.     

Diode-pumped Nd:LGS laser emitting at 888 nm

We present what is, to the best of our knowledge, the first diode-pumped Nd:La₃Ga₅SiO₁₄ (Nd:LGS) laser emitting at 888 nm, based on the ⁴ F _3/2-⁴ I _9/2 transition, generally used for a 904 nm emission. The use of a pump module with 16 passes through the crystal allowed the realization of a Nd:LGS thin-disk laser with 1.41 W of continuous wave (cw) output power at 888 nm. Moreover, intracavity second-harmonic generation (SHG) in cw mode has also been demonstrated with a power of 221 mW at 444 nm by using a BiB₃O₆ (BiBO) nonlinear crystal.     

Application of diffraction methods to the study of volume variations in the composition of a langatate single crystal

A langatate single crystal with the initial composition La₃Ga_5.5Ta_0.5O₁₄, which is grown by means of Czochralski pulling along the 〈0001〉 direction in a weakly oxidizing medium, is investigated via X-ray and neutron diffraction techniques. The crystal is inhomogeneous in color and composition. The middle part of the single crystal is revealed to have a more homogeneous composition than its upper part. It is demonstrated that the color change depends on the amount of oxygen vacancies in different parts of the single-crystal boule.     

Emission features of Ho ion in Nb2O5, Ta2O5 and La2O3 mixed Li2O-ZrO2-SiO2 glasses

Li₂O-ZrO₂-SiO₂: Ho³⁺ glasses mixed with three interesting d-block elemental oxides, viz., Nb₂O₅, Ta₂O₅ and La₂O₃, were prepared. Optical absorption and photoluminescence spectra of these glasses have been recorded at room temperature. The luminescence spectra of Nb₂O₅ and Ta₂O₅ mixed Li₂O-ZrO₂-SiO₂ glasses (free of Ho³⁺ ions) have also exhibited broad emission band in the blue region. This band is attributed to radiative recombination of self-trapped excitons (STEs) localized on substitutionally positioned octahedral Ta⁵⁺ and Nb⁵⁺ ions in the glass network. The Judd-Ofelt theory was successfully applied to characterize Ho³⁺ spectra of all the three glasses. From this theory various radiative properties, like transition probability A, branching ratio β_r and the radiative lifetime τ_r, for ⁵S₂ emission levels in the spectra of these glasses have been evaluated. The radiative lifetime for ⁵S₂ level of Ho³⁺ ions has also been measured and quantum efficiencies were estimated. Among the three glasses studied the La₂O₃ mixed glass exhibited the highest quantum efficiency. The reasons for such higher value have been discussed based on the relationship between the structural modifications taking place around the Ho³⁺ ions.     

Spectroscopic characterization of a Tm3+:SrGdGa3O7 crystal

3 O₇ crystal have been recorded at room temperature and at approximately 8 K. Room-temperature luminescence lifetimes of ¹D₂, ¹G₄, ³H₄, and ³F₄ states have been measured for Tm concentration ranging from [%at.]0.5 to [%at.]9. Based upon these data the crystal field splitting of luminescent states has been derived and radiative transitions rates have been evaluated. Strong self-quenching of luminescence originating in the ¹G₄ and ³H₄ states has been found in this activator–host combination. Peak emission cross section of the potential laser transition at 1800 nm was determined to be 3.9×10^-21 cm² and the gain coefficient versus wavelength was estimated and discussed. Received: 14 April 1998/Revised version: 10 August 1998     

Crystal growth and optical properties of Cr3+, Er3+, RE3+: Gd3Ga5O12 (RE=Tm,Ho, Eu) for mid-IR laser applications

In this paper we report on the optical properties of triply Cr³⁺, Er³⁺, and RE³⁺ (RE=Tm, Ho, Eu) doped Gd₃Ga₅O₁₂ crystals that were grown by the Czochralski method. Optical absorption, near-infrared (NIR), and mid-infrared (mid-IR) fluorescence spectra were characterized for the fabricated crystals and corresponding luminescence decay measurements under 654 nm excitation were also carried out. Based on the analysis of energy transfer process between Er and RE (RE=Tm, Ho, Eu) ions, the energy transfer efficiency (ETE) values were evaluated, correspondingly. From the spectral data of all the studied crystals, it is observed that the co-doped Cr³⁺ ion highly increases the absorption pump power and the three kinds of co-doped RE³⁺ ions depopulate the Er:⁴I_13/2 energy level effectively. The spectral analysis shows that titled rare earth doped crystals are promising materials for ～3.0 μm mid-IR laser applications and among them Cr,Er,Eu:GGG is relatively more suitable due to its excellent optical properties compared with others.     

Improvement of thermal and spectroscopic behavior of Er<Superscript>3+</Superscript>/Ce<Superscript>3+</Superscript> co-doped tellurite glass for lasing materials

Tellurite glasses (TeO₂–ZnO–Nb₂O₅) mono-doped Er³⁺ and co-doped Er³⁺/Ce³⁺ have been prepared using the melt-quenching technique. To evaluate the effect of Ce³⁺ on the structural, thermal stability of glass hosts and fluorescence properties of Er³⁺, X-ray diffraction patterns, Ftir spectra, differential scanning calorimeter curves, absorption spectra, fluorescence emission spectra, fluorescence lifetimes, up-conversion emission spectra of glass samples were measured and investigated. Using Judd–Ofelt theory, we calculated intensity parameters (Ω₂, Ω₄ and Ω₆), spontaneous emission probabilities, the radiative lifetime, luminescence branching factors and the quantum yield of luminescence for ⁴I_13/2 → ⁴I_15/2 transition. The co-doping with Ce³⁺ was effective on the suppression of up-conversion emission of Er³⁺ owing to the phonon-assisted energy transfer: Er³⁺:⁴I_11/2 + Ce³⁺:²F_5/2 → Er³⁺:⁴I_13/2 + Ce³⁺:²F_7/2 which contributed the effective enhancement of 1.53 µm fluorescence emission. The change in optical properties with the addition of Ce³⁺ ions have been discussed and compared with other glasses. Using the Mc Cumber method for the ⁴I_13/2 → ⁴I_15/2 transition, absorption cross-section, calculated emission cross-section, and gain cross-section values support that TZNEr1Ce1 glass is a potential material for developing broad-band and high-gain erbium-doped fiber amplifiers applied for 1.53 µm.     

Synthesis and luminescence properties of Er3+-doped Lu3Ga5O12 nanocrystals

The concentration-dependent luminescence properties of sol–gel-derived nanocrystalline Lu_3(1?x)Er_3xGa₅O₁₂ powders (where x=0.01, 0.05 and 0.1) have been studied. Laser-excited luminescence spectra, emission decays and upconversion luminescence of Er³⁺-doped Lu₃Ga₅O₁₂ nanocrystalline samples have been measured. The decay curve of the (²H_11/2,⁴S_3/2) emission exhibits a non-exponential behavior presumably due to cross-relaxation process. Moreover, near-infrared to visible upconversion luminescence has been observed in the green region for 1.0 mol% Er³⁺ ions in Lu₃Ga₅O₁₂ nanocrystals upon 815 nm excitation. The power dependence of the anti-Stokes luminescence suggests that upconversion is probably achieved through the sequential absorption of two photons. To the best of our knowledge, this is the first report on the preparation and optical properties of Er³⁺-doped Lu₃Ga₅O₁₂ in the form of nanocrystalline powders.     

Photoluminescent properties of Eu 3 +(Dy 3 +)-activated YNb x Ta 1 - x O 4 and REVTa 2 O 9 (RE?=?Y, La, Gd) phosphors from the hybrid precursors

In the context, Eu³⁺ (Dy³⁺)-doped YNb_xTa_1-xO₄ and REVTa₂O₉ (RE=Y, La, Gd) phosphors have been synthesized from the hybrid precursors. Both XRD and SEM indicated the particles present good crystalline state, whose crystalline grain sizes were in the range of 0.5 to 1 μm. Besides, XRD patterns of YNb_xTa_1-xO₄ (x=0.1, 0.2, 0.3, 0.5, 0.9) have shown that the phase has been changed from M^′-type YTaO₄ to M-type YNbO₄ with increasing niobium content. Furthermore, from the luminescent spectra of Eu³⁺-doped YNb_xTa_1-xO₄, it was observed that the ⁵ D ₀–⁷ F ₂ transition of Eu³⁺ was predominated and its intensity increases with increasing niobium content, as well as the intensity ratio of ⁵ D ₀–⁷ F ₂ transition to ⁵ D ₀–⁷ F ₁ transition for Eu³⁺. The optimum concentrations of Eu³⁺ and Dy³⁺ in YNb_0.5Ta_0.5O₄ have been found to be 6 and 5 mol %, respectively. At the same time, the luminescent properties of Eu³⁺ and Dy³⁺ in REVTa₂O₉ (RE=Y, La, Gd) have also been investigated that GdVTa₂O₉:Eu³⁺ (Dy³⁺) presents high luminescence, while LaVTa₂O₉:Eu³⁺ (Dy³⁺) shows weak luminescence. PACS 78.20.-e; 78.55.-m; 61.72.Ss; 32.50.+d; 81.40 Tv     

Spectral and luminescent characteristics of trivalent lanthanide ions in a POCl3-SnCl4 inorganic solvent

We have measured the absorption and luminescence spectra of trivalent lanthanide ions (Pr³⁺, Sm³⁺, Tb³⁺, Dy³⁺, Ho³⁺, Er³⁺, Tm³⁺, and Yb³⁺) in the visible and near-IR wavelength ranges in a POCl₃-SnCl₄ inorganic solvent. In terms of the Judd-Ofelt model, the oscillator strengths of absorption bands, the probabilities of radiative transitions, the luminescence branching coefficients, the lifetimes of excited states, and the luminescence quantum yields have been calculated. Possibilities of creating new laser media have been evaluated. A conclusion is drawn regarding the symmetry of the environment of trivalent lanthanide ions in the POCl₃-SnCl₄ solvent.     

Studying acoustic-wave fields in langasite-family crystals using the BESSY II synchrotron radiation source

The process of the excitation and propagation of pseudosurface acoustic waves in crystals of the langasite family is studied via X-ray diffractometry for the first time. The investigations are carried out using the BESSY II synchrotron radiation source in the double-crystal X-ray diffractometer scheme. The process of pseudosurface acoustic wave propagation is studied based on an analysis of the diffraction spectra of acoustically modulated crystals. Both the velocities of the pseudosurface acoustic waves and the power flow angles of the acoustic energy are measured for the first time. The pseudosurface acoustic wave is shown to be flowing. Surface and pseudosurface acoustic waves generated by an interdigital transducer in the Z cut of a La₃Ga_5.5Ta_0.5O₁₄ crystal are compared.     

Ga2O3组分对Tm3+掺杂GeO2-Ga2O3-Li2O-BaO-La2O3玻璃的光谱性能影响

制备了Tm³⁺(8.0mol%)掺杂(77-x)GeO₂-xGa₂O₃-8Li₂O-10BaO-5La₂O₃(x=4,8,12,16)系列玻璃.系统地研究了Ga₂O₃从4mol%变化到16mol%时,玻璃的光谱性质与热学性质的变化规律.差热分析表明,随着Ga₂O₃含量的增加,锗酸盐玻璃的热稳定性增加.运用Judd-Ofelt(J_O)理论计算得到了Tm³⁺在不同Ga₂O₃含量的GeO₂-Ga₂O₃-Li₂O-BaO-La₂O₃玻璃中的J-O强度参数(Ω₂,Ω₄,Ω₆)及Tm³⁺各激发能级的自发跃迁概率、荧光分支比以及辐射寿命等光谱参量.在808nm激光二极管的激发下,测试并分析了Ga₂O₃对Tm³⁺荧光光谱特性的影响.随着Ga₂O₃从4mol%增加到16mol%,Tm³⁺在1.8μm处的荧光强度呈现先减弱后增强的特性.当Ga₂O₃含量大约在12mol%时,Tm³⁺在1.8μm处的荧光强度最弱,受激发射截面达到最小.还初步讨论了Ga₂O₃对玻璃结构与光谱参数的影响规律. 关键词： 3+掺杂锗酸盐玻璃')" href="#">Tm³⁺掺杂锗酸盐玻璃 光谱性能 Judd-Ofelt参数 热稳定性