Yb to Er energy transfer and rate-equations formalism in the eye safe laser material Yb:Er:Ca2Al2SiO7

Rate equations formalism is used to predict the population ratio of the Er^{3+ 4}I_13/2 levels involved in the 1.55 μm laser transition in the Yb:Er:CAS laser materials. An effective Yb → Er energy transfer, favourable to the Er³⁺ 1.55 μm laser emission, is demonstrated in this laser host. Indeed, the Yb → Er transfer and the Er → Yb back transfer rates are calculated to be 6 x 10⁻¹⁶ and 0.45 x 10⁻¹⁶ cm³ s⁻¹, respectively. Attempts of codoping the system with Nd³⁺, Eu³⁺ and Ce³⁺ have been realised in order to increase the population of the Er^{3+ 4}I_13/2 laser emitting level. Best results are obtained with Ce³⁺ ion since in the sample containing 6 x 10²⁰ Ce³⁺/cm³, the Er^{3+ 4}I_11/2 level lifetime is divided by a factor of 3 while the Er^{3+ 4}I_13/2 fluorescence lifetime remains unaffected. On the contrary, codoping with Nd³⁺ or Eu³⁺ ions simultaneously decreases the Er^{3+ 4}I_11/2 and ⁴I_13/2 kinetics parameters. The role of the other parameters such as Yb/Er concentrations ratios is also discussed.     

Optical properties and energy transfer among Nd in Nd:Ca2Al2SiO7 crystals for diode pumped lasers

The energy levels of neodymium in the Nd³⁺:Ca₂Al₂SiO₇ (CAS) laser material with gehlenite structure are reported. As the Nd³⁺:Ca₂Al₂SiO₇ compound presents a broad absorption around 806 nm, it is a good candidate for diode pumped laser. The ⁴F_3/2→⁴I_9/2 and ⁴F_3/2→⁴I11/2 emission have been recorded and the fluorescence branching ratios calculated from the Judd-Ofelt analysis are 0.41 and 0.47 respectively. The emission cross section at 1.06 μm (⁴F_3/2→⁴I11/2 transition) is 5 × 10^-20 cm². The decay profiles of the Nd³⁺ emission have been analyzed for several Nd³⁺ concentrations using the kinetic microparameters related to the cross relaxation ( and R₀≈6 Å) and the energy migration probabilities ( ). In the Nd:CAS laser material, the optimal concentration corresponding to the maximum of the fluorescence intensity is determined to be around 2.7 × 10²⁰ Nd³⁺ ions cm^-3. The Nd³⁺-Nd³⁺ interactions are not very strong in this material as the optical concentration value is two times higher than in the Nd:YAG laser material.     

Energy transfer luminescence in (Eu,Nd) : tellurite glass

Here, we bring out an infrared transmitting new optical glass based on TeO₂ added with AlF₃ and LiF, containing dual rare earth ions (Eu³⁺,Nd³⁺) as the dopants with a purpose to examine their luminescence and also the decay times pertaining to a prominent transition of Eu³⁺ (⁵D₀ → ⁷F₂ at 615 nm) as a function of temperature both in the presence and absence of Nd³⁺ ions. The energy transfer rates (W_tr), critical distances (R₀) and transfer efficiencies (η_tr) have been evaluated based on the measured lifetime data of this glass.     

Synthesis and the luminescent properties of europium-activated Ca2SnO4 phosphors

The synthesis and photoluminescent (PL) properties of calcium stannate crystals doped with europium grown by mechanically activated in a high energy vibro-mill have been investigated. The characteristics of Ca₂SnO₄:Eu³⁺ phosphors were found to depend on the amounts of europium ions. The XRD profiles revealed that the system, (Ca_1−xEu_x)₂SnO₄, could form stable solid solutions in the composition range of x = 0–7% after being calcined at 1200 °C. The calcined powders emit bright red luminescence centered at 618 nm due to ⁵D₀ → ⁷F₂ electric dipole transition. Both XRD data and the emission ratio of (⁵D₀ → ⁷F₂)/(⁵D₀ → ⁷F₁) reveal that the site symmetry of Eu³⁺ ions decreases with increasing doping concentration. The maximum PL intensity has been obtained for 7 mol% concentration of Eu³⁺ in Ca₂SnO₄.     

Spectroscopic evidence of inhomogeneous distribution of Nd in YVO4, YPO4 and YAsO4 crystals

Nd³⁺ : YVO₄ is one of the most interesting laser hosts for micro and diode-pumped solid state lasers. We have studied magnetic and optical properties of Nd³⁺ in three zircon type crystals YMO₄ (M=V, As, P). In particular, Nd³⁺ ions exhibit in the three hosts a multisite character observed in the absorption and emission spectra. However, the emission and its dynamics are strongly dependant on the reabsorption mechanisms. In Nd : YVO₄, single crystals containing 7 ± 1 × 10¹⁸ Nd³⁺ ions/cm³, the lifetime is 95 ± 2 μs in good agreement with the calculated radiative lifetime. Electron Paramagnetic Resonance (EPR) measurements are performed to identify the nature of the different substitution sites for Nd³⁺ ions. Nd³⁺ ions are found to be inhomogeneously distributed in tetragonal D_2d symmetry sites, in isolated ions, “shallow clusters” and pairs. Proportions of the different local environments depend on the total neodymium concentration. For instance, 15% of the Nd³⁺ ions are gathered in Nd³⁺–Nd³⁺ pairs for 7.2 ± 0.2 × 10¹⁹ Nd³⁺ ions/cm³.     

Infrared absorption and Zeeman effect in Nd doped YVO4

Low temperature infrared transmission studies of Nd³⁺ doped YVO₄ were performed, under a magnetic field B c, in the 1800–8000 cm⁻¹ range of the ⁴I_9/2→⁴I_11/2, ⁴I_13/2, and ⁴I_15/2 Nd³⁺ crystal-field transitions. Good agreement is obtained between the experimental and calculated g-factors. Frequencies of the satellites in the ⁴I_9/2→⁴F_3/2 transitions of the Nd³⁺ isolated ion confirm the presence of ferromagnetic interactions between pairs of coupled Nd³⁺ ions that lift the Kramers doublet degeneracies of their ground state and excited multiplets.     

Effect of heat treatment on photoluminescence behavior of BaMgAl10O17:Eu phosphors

The blue phosphor of BaMgAl₁₀O₁₇:Eu²⁺ (BAM) powders were prepared by solid-state reaction. The thermal degradation of BAM phosphor significantly reduces the intensity of the blue emission. BAM is reduced by an amount of 50% after heating at around 800 °C for 1 h. Photoluminescence (PL) excitation and emission spectra showed that the blue emission of 450 nm peak decreased with increasing annealing temperature. The ⁵D₀→⁷F₁ and ⁵D₀→⁷F₂ transition of Eu³⁺ were observed at 590 and 615 nm emission lines over 1100 °C. Electron paramagnetic resonance (EPR) spectrum also detected two signals of Eu²⁺, corresponding to g=3.7156(9) for 88 mT, and g=2.9507(9) for 133 mT. X-ray absorption near edge structure (XANES) spectrum decreased the intensity of Eu²⁺ for 6977 eV with increasing annealing temperature, while high-energy peak of Eu³⁺ for 6984 eV was increased. The combined use of X-ray and neutron data by the Rietveld refinement appears to support that the secondary phase of EuMgAl₁₁O₁₉ magnetoplumbite structure in BAM may be formed by heat treatment.     

Improved optical photoluminescence by charge compensation in the phosphor system CaMoO4:Eu

It has been found that charge compensated CaMoO₄:Eu³⁺ phosphors show greatly enhanced red emission under 393 and 467 nm-excitation, compared with CaMoO₄:Eu³⁺ without charge compensation. Two approaches to charge compensation, (a) 2Ca²⁺ → Eu³⁺ + M⁺, where M⁺ is a monovalent cation like Li⁺, Na⁺ and K⁺ acting as a charge compensator; (b) 3Ca²⁺ → 2Eu³⁺ + vacancy, are investigated. The influence of sintering temperature and Eu³⁺ concentration on the luminescent property of phosphor samples is also discussed.     

Valency states of Yb, Eu, Dy and Ti ions in Li2B4O7 glasses

Absorption and emission spectra of Eu and Dy, Yb and Ti ions in Li₂B₄O₇ glasses grown in oxygen and hydrogen gas atmospheres were measured for valency states and lattice-sites analysis. For the Li₂B₄O₇ glass doped with Eu²⁺, Eu³⁺ and Dy³⁺ ions which were grown in oxidizing and reducing atmospheres, absorption and emission bands due to these ions were investigated before and after γ-irradiation. For the Yb³⁺-doped Li₂B₄O₇ glass, a weak, broad band was observed near the sharp 976.3 nm absorption band. The origin of this band is discussed in comparison with other glasses. Moreover, irradiation experiments using γ-rays were also performed in order to investigate the possibility of valency change of Yb ions. It was found that Ti⁴⁺ ions, which are produced under oxidizing atmosphere, change to Ti³⁺ ions after γ-irradiation with a dose of 10⁵ Gy. An additional absorption band observed at about 500 nm is due to the Ti³⁺ ions accompanied by charge-compensating vacancy and does not give any emission.     

Spectroscopic analysis and the effects of color centers on the laser performance of Nd: CaZn2Y2Ge3O12

Spectroscopic and EPR investigations of Nd³⁺-doped CaZn₂Y₂Ge₃O₁₂ (CAZGAR) have been performed. The absorption, fluorescence, excitation spectra and fluorescence lifetime have been measured at room temperature. The Judd-Ofelt theory has been applied to the measured optical absorption intensities to predict the radiative decay rates, branching ratios, and peak stimulated emission cross section from the metastable ⁴F_3/2 state to the ⁴I_9/2 manifold. The fluorescence lifetime of the ⁴F_3/2 level of Nd³⁺ at low concentration in this host was measured to be 285 ± 10 μs, which is longer than that for Nd³⁺: YAG. Color centers located at zinc octahedral sites have been produced in these crystals by ultraviolet irradiation and have been detected by EPR techniques. The effects of the color centers on the potential laser characteristics of this materials are discussed.     

Spectroscopic investigation of Nd ion in LiNbO3, MgO:LiNbO3 and LiTaO3 single crystals relevant for laser applications

The polarized absorption and luminescence properties of Nd³⁺ doped isostructural LiNbO₃, MgO:LiNbO₃ and LiTaO₃ nonlinear bulk single crystals are reported. Pump-probe experiments associated with the Judd-Ofelt approach are used to estimate two types of room temperature cross sections: polarized emission cross sections of the dominant ⁴F_3/2 → ⁴I_1//2 transition near 1085 and 1093 nm and polarized excited-state absorption cross sections in the same spectral domain and in the green spectral range corresponding to self frequency doubling. Self frequency-doubling results are also given in Nd:LiNbO₃ and Nd:MgO:LiNbO₃ versus sample temperature.     

Optical properties of rare earth ion (Nd, Er and Tb)-doped alumina films prepared by the sol–gel method

Rare earth ion (Nd³⁺, Er³⁺ and Tb³⁺)-doped alumina films were prepared by the sol–gel method using aqueous alumina sol. The effects of dopant concentration and treatment temperature on the optical properties, absorption and emission were examined for the doped films. Alumina films prepared by this method gave a high dopant concentration (0–15 mol% per alumina). Significant concentration quenching did not occur in this concentration range. The emissions from ⁵D₃ and ⁵D₄ of Tb³⁺-doped film reflected sensitively a matrix environment around Tb³⁺ ions. Er³⁺- and Nd³⁺-doped alumina films resonantly excited by cw Ti–sapphire laser (800 nm) showed upconversion emission at room temperature. The former gave 548 nm (⁴S_3/2→⁴I_15/2) and 640 nm (⁴F_9/2→⁴I_11/2) signals, and the latter 640 nm (⁴G_7/2→⁴I_11/2), which were dependent on alumina.     

Optical properties and laser performance of neodymium doped fluoroapatites SrxCa5−x(PO4)3F (x = 0, 1, 2, 3, 4, and 5)

Nd doped fluoroapatites Sr_xCa_5−x(PO₄)₃F(S_xC_5−xPF, X = 0, 1, 2, 3, 4, and 5) single crystals have been grown by the Czochralski technique. Their polarized absorption and emission spectra have been recorded at room temperature and used to calculate the absorption and stimulated emission cross sections. Broadening of the absorption and emission bands is observed for Nd³⁺ in the solid solutions SPF-CPF compared to Nd³⁺ in CPF or SPF. 1% Nd:S_xC_5−xPF, X = 0, 2, 3, 4, and 5, laser rods have been tested in a cavity longitudinally pumped by a 1 W AlGaAs laser diode and compared to Nd:YAG and Nd:YVO₄ rods. All fluoroapatites exhibit very good laser performance with low thresholds and high slope efficiencies, higher than in the case of YAG and equal to the YVO₄ samples. The dependance of the laser output power versus the diode temperature has also been measured for all materials. The laser output was found to be as sensitive to the diode temperature fluctuations for fluoroapatites as for YAG.     

Crystal growth and spectral properties of pure and Co-doped Mg3B2O6 crystal

Novel pure and cobalt-doped magnesium borate crystals (Mg₃B₂O₆) have been grown successfully by the Czochralski technique for the first time. Crystal growth, X-ray powder diffraction (XRD) analysis, absorption spectrum, fluorescence spectrum as well as fluorescence decay curve of Co²⁺:Mg₃B₂O₆ (MBO) were described. From the absorption peaks for the octahedral Co²⁺ ions, the crystal-field parameter Dq and the Racah parameter B were estimated to be 943.3 cm⁻¹ and 821.6 cm⁻¹, respectively. The fluorescence lifetime of the transition ⁴T₁(⁴P) → ⁴T₂ centered at 717 nm was measured to be 9.68 ms.     

Highly enhanced luminescence of SrB4O7:Eu phosphor prepared by the combustion method using glycine as fuel

Eu²⁺ ion doped into SrB₄O₇ matrix was prepared by combustion method heated at 900 °C in air, using urea (U) or glycine (G) as fuels in different ratios (U100, A10, A25, G10, G25, G75, and G100). In some compositions, ammonium acetate (AA) was used to reduce the exothermicity of combustion reaction. X-ray diffraction and luminescence spectroscopy were used to characterize the material. The high intense emission band at 367 nm is assigned to 4f⁶5d → 4f⁷(⁸S_7/2) transition arisen from divalent europium ion. It is observed that the interconfigurational transition is dependent on the molar ratio of glycine:urea fuels. Glycine fuel favors Eu²⁺ formation in SrB₄O₇ host lattice prepared by combustion method.     

Temperature dependent luminescence in (Eu, Dy) doped tellurite glass

This short paper reports both the photoluminescence and the lifetime measurements of a prominent emission transition (⁵D₀→⁷F₂) of Eu³⁺ both in the presence and absence of the codopant rare earth ion (Dy³⁺) in an optical glass of the composition (79−x)TeO₂+6AlF₃+15LiF+xLn₂O₃ as a function of temperature down to 10 K.     

YVO4∶Eu3+,Bi3+红色荧光粉的水热合成及其荧光性能

以Y₂O₃、Eu₂O₃、Bi(NO₃)₃·H₂O、浓HNO₃、偏钒酸铵、氨水、无水乙醇和一缩二乙二醇为原料,采用聚乙烯吡咯烷酮(PVP)辅助水热法合成YVO₄: Eu³⁺, Bi³⁺纳米颗粒。使用X射线衍射(XRD)、扫描电镜(SEM)、红外光谱(IR)和荧光光谱(FL)等手段对产品进行了表征和分析。结果表明：合成的样品为YVO₄: Eu³⁺, Bi³⁺纳米颗粒,均具有四方晶相结构,其微结构随反应溶液的的pH值变化。YVO₄: Eu³⁺, Bi³⁺纳米颗粒在619 nm处有较强的红光发射(电偶极跃迁⁵D₀→⁷F₂),在594 nm有较弱的橙光发射(磁偶极跃迁⁵D₀→⁷F₁)。随着Eu/Bi比值的增大材料的荧光先增强后减弱,在Eu/Bi比值为5时样品的红光发射最强。溶液的pH值影响YVO₄: Eu³⁺, Bi³⁺纳米晶的发光强度,其中pH值为10时的样品其红光发射最强。并探讨了YVO₄: Eu³⁺, Bi³⁺纳米晶的发光机理。     

Optical properties of Nd-doped Ca3(VO4)2 single crystal fiber

Optical absorption and photoluminescence of Ca₃(VO₄)₂ single crystal grown by a floating-zone technique and containing Nd³⁺ ions were investigated. High absorption coefficients and broadening of most absorption bands are present at 300 K, while substructures in some of the same bands can be evidenced at 12 K. Most features of measured spectra are characteristic of random occupation of more than a single Ca²⁺ site by the Nd³⁺ ion and of distortions provoked by different charge compensation mechanisms involving oxygen vacancies promotion in the crystal lattice. Nd³⁺ optical properties were studied by using the Judd-Ofelt theory to calculate the spectral parameters relevant for laser applications.     

Preparation and photoluminescence properties of Eu-doped Ga2O3 nanorods

GaOOH:Eu³⁺ nanorods with different aspect ratios were prepared by hydrothermal method at 140 °C. - and β-Ga₂O₃:Eu³⁺ were converted from as-prepared GaOOH:Eu³⁺ particles by calcination at 500 and 850 °C, respectively. The products were characterized with X-ray diffraction (XRD), transmission electron microscope (TEM) and photoluminescence (PL). Results show that solution pH values play a key role in the formation of the GaOOH:Eu³⁺ powders with different morphologies and - and β-Ga₂:Eu³⁺ inherit the morphology of GaOOH:Eu³⁺ exactly. The photoluminescence characteristics of β-Ga₂O₃:Eu³⁺ were also investigated. Experimental results reveal that the color purity of β-Ga₂O₃:Eu³⁺ nanorods with high aspect ratio is enhanced in comparison with β-Ga₂O₃:Eu³⁺ nanorods with low aspect ratio.     

Investigation in the VUV range of the excitation efficiency of the Tb ion luminescence in Y3 (Alx, Gay)5O12 host lattices

VUV excitation spectra of the visible luminescence of Tb³⁺ activated Y₃(Al_x, Ga_y)₅O₁₂ compounds and their diffuse reflectance spectra are presented. The crystal field strength, the absorption threshold of the matrix and the external quantum efficiency (Q_ext) associated with the different excitation mechanisms (4f⁸ → 4f⁷ 5d transitions in the activator or interband transitions in the host) decrease when the gallium concentration increases. Such variations are ascribed to an increase of the oxidizing character of the host matrix along with the gallium concentration. The decrease of the external quantum efficiency (Q_ext) is discussed in terms of a trivalent rare-earth ion (RE³⁺) configurational coordinate model and related to the intervention of the photoionized state [RE³⁺ → RE⁴⁺ + e⁻]. The non radiative relaxation rate increases when this state is stabilized.affd