Standard Judd Ofelt Research Articles

Tm3+ doped CaF2 based oxyfluroborosilicate glasses and glass ceramics for visible and NIR lasers

The structural and luminescence properties of Tm3+ doped CaF2 based oxyfluoroborosilicate glasses and glass ceramics were discussed. The critical glass ceramic (BSTm1.0GC2) nature was obtained through different heat treatment processes as 450 oC for 1 h and the concentration of Tm3+ ions was optimized as 1.0 mol% for efficient emission. The spectroscopic and laser characteristic parameters were evaluated applying the standard Judd-Ofelt theory. The emission of blue light through 1D2 → 3F4 transition was studied by exciting at 360 nm UV wavelength. Upon 808 nm laser excitation, the glasses and glass ceramics produce 1.46 μm emission through 3H4 → 3F4 transition. The effective bandwidth (114.99 nm), stimulated emission cross-section (14.30×10–21 cm2), gain bandwidth (1644.74×10–28 cm3), figure of merit (10.21×10–24 cm2s) and the quantum yield (76%) of 3H4 → 3F4 transition made the BSTm1.0GC2 suitable as gain medium for 1.46 μm NIR fiber laser applications.

Er3+ -doped oxyfluoroborosilicate glass ceramics with embedded CaF2 nanoparticles for 1.53 μm broad band applications

The CaF2 based oxyfluoroborosilicate glasses and glass ceramics doped with Er3+ ions were prepared via melt quench process followed by heat treatment and characterized for 1.53 μm broadband applications. The optimized glass ceramic sample was obtained at 450oC/1h heat treatment. The Er3+ concentration was optimized as 1.0 mol% for efficient emission at 460 nm excitation through concentration dependent luminescence analysis. The spectroscopic parameters such as Ωλ=2,4,6 parameters and the radiative parameters such as spontaneous transition probability rates (AR), branching ratios (βR) and decay times (τR) were calculated applying the standard Judd-Ofelt theory. The effective bandwidth (Δλeff), stimulated emission cross-section (σe), gain bandwidth (σe×Δλeff), quantum efficiency (η) and figure of merit (σe×τR) were calculated as 25.78 nm, 13.42×10-21 cm2, 3.46×10-26 cm3, 82.83% and 5.32×10-23 cm2s, respectively for the optimized glass ceramic sample. The exchange type of energy transfer among the excited Er3+ ions results the quenching in luminescence and the non-exponentiality in decay curves. The systematic investigations carried out indicate that the glass ceramic obtained at 450oC/1h heat treatment was proficient for 1.53 μm broadband fiber lasers and optical amplifiers in S and C band communication window.

Structural and spectroscopic studies of Er3+ in different fluorophosphate glasses for green laser and fibre amplifier operations

Erbium activated fluorophosphate glasses were synthesized with conceived characteristic combination, 59.5NH4H2PO4+15ZnO+15BaF2+10X+0.5Er2O3(X = LiF, NaF, CaF2, SrF2, AlF3) by melt quenching route. Based on the mass densities, and refractive indices, other physical properties i.e., dielectric constant (ε), reflection losses, molar refraction, internuclear distance and molar volume are determined. XRD has confirmed the non-crystalline character of the prepared glass samples. FTIR, FT-Raman have been employed to study the structural characteristics. Various radiative properties have been inferred through optical absorption measurements by standard Judd–Ofelt procedure. By excitation at 379 nm, all the glass hosts doped with constant concentration 0.5 mole% of Er3+have yielded intense green emission peak due to the transition 4S3/2 → 4I15/2 at 545 nm. Characteristic emission transition 4I13/2 → 4I15/2 at wavelength 1.53 μm has been studied extensively. Particularly the parameters related to that transition namely, stimulated emission cross-sections (σ e) and optical gains (G) are calculated from emission spectra. Among all the fluorophosphate glasses, the one which has shown higher σ e, and G values is sodium fluorophosphate (NFPE) glass. It is recommended for optical fiber amplification and NIR laser usage.

Transition intensities of trivalent lanthanide ions in solids: Extending the Judd-Ofelt theory

We present a modified version of the Judd-Ofelt theory, which describes the intensities of f-f transitions for trivalent lanthanide ions (Ln3+) in solids. In our model, the properties of the dopant are calculated with well-established atomic-structure techniques, while the influence of the crystal-field potential is described by three adjustable parameters. By applying our model to europium (Eu3+), well-known to challenge the standard Judd-Ofelt theory, we are able to give a physical insight into all the transitions within the ground electronic configuration, and also to reproduce quantitatively experimental absorption oscillator strengths. Our model opens the possibility to interpret polarized-light transitions between individual levels of the ion-crystal system.

Judd-Ofelt spectroscopic properties of Er3+-doped NaLa(WO4)2 polycrystalline powder

Er3+-doped NaLa(WO4)2 is a promising phosphor material for applications in many fields including the ratiometric thermometry based on thermal effect of fluorescence intensity ratio (FIR) of green fluorescence of Er3+, which is directly correlated with Judd-Ofelt parameters Ωi (i = 2, 4, 6). Present paper reports synthesis and Judd-Ofelt spectroscopic properties of Er3+-doped NaLa(WO4)2 µm-sized phosphor. The phosphor was synthesized by solid-state chemical reaction and characterized by X-ray diffraction and Raman scattering techniques. The results show that the phosphor is dominated by NaLa(WO4)2 crystalline phase and has a maximum phonon energy 927 cm−1. Judd-Ofelt analysis was done for the phosphor using a safe, reliable method based on diffuse reflection spectrum and Er3+ 1.5 μm fluorescence lifetime. First, diffuse reflection spectrum of the phosphor was measured and relative absorption spectrum was calibrated from it using Kubelka-Munk theory. Second, Er3+ 1.5 μm fluorescence lifetime of the phosphor was measured and absorption cross-section spectrum was obtained based on the assumption that the 1.5 μm emission has 100% quantum efficiency. Finally, based on the absorption cross-section spectrum, standard Judd-Ofelt analysis was carried out to extract the Ωi. Radiative rate, fluorescent branch ratio and radiative lifetime of some transitions have been obtained from the known Ωi values. In addition, FIR proportional factor was evaluated in terms of Ωi and compared with those values of other materials. The result shows that the phosphor has a better prospect for the application in ratiometric thermometry.

Judd-Ofelt parameters of RE3+-doped fluorotellurite glass (RE3+= Pr3+, Nd3+, Sm3+, Tb3+, Dy3+, Ho3+, Er3+, and Tm3+)

Fluorotellurite glasses are a family of materials presenting a multitude of interesting optical properties with a wide range of applications. As with other glasses, having a full understanding of the optical properties requires an in-depth spectroscopic characterization. Subsequently, the Judd-Ofelt parameters (Ω2, Ω4, Ω6) have been obtained for the trivalent rare-earth, RE3+ ions family introduced as dopants in a fluorotellurite glass with a composition (in mol%): 85 TeO2 - 10 PbF2- 2.5 AlF3 - 2.5 REF3 (RE3+ = Pr3+, Nd3+, Sm3+, Tb3+, Dy3+, Ho3+, Er3+ and Tm3+). These parameters were calculated from the absorption spectra for each RE3+. In the case of the Pr3+, the intensity parameters have been calculated using both the standard Judd-Ofelt theory and the modified theory developed by Kornienko, Kaminski, and Dunina. To further characterize the materials, the refractive index has been considered both as constant and dependent on the wavelength. Both cases were considered in the calculation of the Judd-Ofelt parameters. These results were contextualized and substantiated with other spectroscopic analyses that were undertaken in previous works. The resulting estimates were subsequently compared with other glass matrices to infer any differences between the ionic character and the behavior of the dopant to ligand bounds inside different matrices.

Synthesis and characterization of Er3+/Cu+-codoped fluorophosphate glasses

NaPO3-ZnF2 binary fluorophosphate glasses doped with trivalent erbium and monovalent copper were synthesized by the conventional melting and casting method using ErF3 and CuCl as starting materials. The samples were systematically investigated using X-ray diffraction (XRD), energy dispersive X-ray spectroscopy (EDS), Fourier-transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) analysis. X-ray powder diffraction patterns confirmed that the as-prepared compounds were all amorphous. The glass transition temperature (Tg) was observed around 230 °C by DSC analysis, while the thermal stability range (ΔT) was estimated to be between 90 and 140 °C. The measured value of the refractive index (n) was measured as 1.502 at a wavelength of 632.8 nm. Thermal annealing of the samples was performed at different temperatures above Tg for various heat-treatment times. During these steps, monovalent copper and sodium ions were expected to be reduced, forming metallic nanoparticles. This transformation lead to coloration changes, depending on the annealing time and temperature, with respect to the transparency of the glasses. These spectroscopic changes are related to the plasmonic effects induced by the presence of both Cu and Na metallic nanoparticles, which promote red shift due to absorption. The VIS-NIR absorption spectra of the prepared glasses were investigated in the frame work of standard Judd-Ofelt (J-O) theory, which was used to determine the J-O intensity parameters, radiative transition probabilities and branching ratios for Er3+ ions embedded in the glasses. The calculated intensity parameters (Ω2,4,6) were compared to those obtained for Er3+ in several other glasses.

TeO2-WO3-GeO2-NdF3 glasses for 1.06 μm fiber lasers: An optical analysis

The TeO2-WO3-GeO2-NdF3 (TWGNd) glasses containing various amounts of NdF3 were synthesized through melt-quenching method and analyzed for 1.06 μm fiber lasers. The index of refraction increases with the addition of NdF3 content at 5893 Å wavelength. Different spectroscopic and radiative parameters were determined applying the standard Judd-Ofelt theory. The TWGNd glasses exhibit three emission transitions peaked at ∼0.90, ∼1.06 and ∼1.33 μm corresponding to 4F3/2 → 4I9/2, 4I11/2, 4I13/2 transitions, respectively at 808 and 514.5 nm laser excitations. A quenching in luminescence was noticed beyond 1.0 mol% of NdF3 content. The saturation intensities that were used to know the threshold power of input source for laser operation were determined. The observed results show that the TWGNd10 glass has the best choice to develop 1.06 μm fiber lasers.

Standard and modified Judd-Ofelt theories in Pr3+-doped calcium aluminosilicate glasses: A comparative analysis

The small energy difference between the fundamental level and the first opposite parity configuration of Pr3+-doped hosts is particularly challenging for the characterization of radiative transitions using the Judd-Ofelt theory, although modified versions of the theory have been proposed in the past for the investigation of praseodymium doped materials. Here, we present a detailed spectroscopic investigation on two sets of calcium aluminosilicate glasses, with 34 wt% of SiO2 (CAS) and with 7 wt% of SiO2 (LSCAS), doped with different concentrations of Pr3+ (0.5, 1.0 and 2.0 wt%). We use the standard Judd-Ofelt theory to characterize the glasses and the results and derived spectroscopic quantities — such as transition probabilities, radiative lifetimes and branching ratios — are compared to results obtained by the modified Judd-Ofelt theories. The analysis showed that the modified theories could lead to smaller values of root mean square deviations. However, a better agreement between experimental data and the standard theory was achieved when the derived spectroscopic quantities are taken into account. Moreover, the branching ratios of the P03→H43 and D21→H43 transitions were over 60% for both glass hosts, suggesting its potential use as solid-state laser devices.

Spectroscopic properties of lanthanide based metal-organic framework [Nd(C4H5O6)(C4H4O6)][3H2O]: Theoretical and experimental approaches

The spectroscopic properties of a lanthanide based MOF, [Nd(C4H5O6)(C4H4O6)][3H2O] have been discussed in detail. Semiempirical quantum methods are used to calculate the singlet and triplet excited states, and Uv and IR spectra of the organic part of the MOF. The experimental absorption and luminescent spectra of the MOF are also reported. The experimental absorption spectrum shows the characteristic transition of Nd(III) ion as well as the transitions of the ligands. The experimental line strengths of all the observed transition are calculated. The standard Judd-Ofelt theory is used to calculate intensity parameters, transition probabilities, branching ratios, and radiative lifetimes for [Nd(C4H5O6)(C4H4O6)][3H2O] MOF. The JO parameters are used to calculate various excited state properties. Upon excitation by ultraviolet and visible photons, the complex emits in blue and green regions respectively. The blue emission is ligand (tartrate) based assigned to S1→ S0 transition whereas green emission is metal based assigned to 4G9/2 + 4G7/2 → 4I11/2 transitions. No antenna effect is observed in NTT-MOF. It is because of the large gap between the triplet energy level of the tartrate ligand and the resonance energy level 4F3/2 of the Nd(III) ion.

Spectroscopy of Nd3+ luminescence centres in Li2B4O7:Nd, LiCaBO3:Nd, and CaB4O7:Nd glasses

The electron paramagnetic resonance (EPR), optical absorption, luminescence (emission and excitation) spectra as well as luminescence kinetics of the Nd3+ centres in a series of borate glasses with Li2B4O7:Nd, LiCaBO3:Nd, and CaB4O7:Nd compositions containing 0.5 and 1.0 mol% Nd2O3 have been investigated and analysed. Using EPR and optical spectroscopy data it was shown that the Nd impurity is incorporated into the network of investigated glasses as Nd3+ (4f3, 4I9/2) ions, exclusively. All observed f – f electronic transitions of the Nd3+ centres in optical absorption and luminescence spectra of the investigated glasses were identified. Local structure of the Nd3+ luminescence centres in the borate glasses network is proposed. Theoretical oscillator strengths (ftheor) and phenomenological intensity parameters (Ω2, Ω4, Ω6) for observed Nd3+ absorption transitions containing 1.0 mol% Nd2O3 have been determined using standard Judd–Ofelt theory. The spectroscopic parameters of relevance to laser applications such as the radiative transitions rate (Wr), luminescence branching ratio (β), radiative lifetime (τrad), and emission cross-section (σem) for Nd3+ centres in the Li2B4O7:Nd, LiCaBO3:Nd, and CaB4O7:Nd glasses have been calculated. Luminescence decay curves of the Nd3+ centres from the 4F3/2 emitting level for all investigated glasses were satisfactory described by single exponential decay. The obtained experimental lifetimes were compared with those calculated and quantum efficiency (η) of the 4F3/2 → 4I11/2 transition for Nd3+ centres in the investigated glasses were estimated. Based on the obtained results it can be concluded that the further efforts should be made to improve the Nd-doped borate glasses parameters relevant for neodymium solid state lasers with LED pumping.

Optical properties of Er3+-Yb3+ codoped Cd.7Sr.3F2 mixed single crystals

Absorption, excitation, fluorescence and decay spectra are carried out at room temperature on Er3+ (1%), Yb3+ (4%): Cd.7Sr.3F2 mixed single crystals. These crystals, with a good optical quality, are grown by the standard Bridgman method. This work concerns mainly the spectroscopic properties of the Er3+ ions incorporated in a fluorite-type crystal. Using the room temperature absorption spectra, the standard Judd–Ofelt (JO) model is applied to absorption intensities of Er3+ to obtain the three phenomenological intensity parameters by the least square fit procedure. The values obtained are in accordance with those of other fluoride hosts with good root mean square fitting. Compared to oxide materials, fluoride materials have, in general, low values ​​of Ω2. The low value of Ω2 is correlated to the cubic nature of the site occupied by the rare earth in the host matrix. These JO intensity parameters are then applied to determine the radiative transition probabilities (AJJ′), radiative lifetimes (τrad) and branching ratios (βJJ′) of Er3+ transitions. The green emission generated by the Er3+ ions directly excited in UV level, consisting in three well-resolved major lines, is more intense than the one. We have measured the fluorescence lifetime, the cross-section emission, the gain and the radiative quantum efficiency for both green and red band emissions. The obtained results are in good agreement with those of other fluoride laser crystals. From, the obtained spectroscopic data we suggest that Cd.7Sr.3F2 may offer green and red visible laser emission when doped with Er3+ ions.

Spectroscopic properties of Er3+-doped fluorotellurite glasses containing various modifiers

We have investigated the optical and spectroscopic properties of new Er3+-doped fluorotellurite glasses with the basic molar composition 75%TeO2-10%P2O5-10%ZnO-5%PbF2, modified by replacing 5%TeO2 by four various metal oxides, namely MgO, PbO, SrO and CdO. The ellipsometric data have provided a Sellmeier-type dispersion relation of the refractive index of the investigated glasses. The optical absorption edge has been described within the Urbach approach, while the absorption and fluorescence spectra have been analyzed in terms of the standard Judd–Ofelt theory along with the photoluminescence decay of the 4I13/2 and 4S3/2 levels of the Er3+ ion. The absorption and emission spectra of the 4I15/2 ↔ 4I13/2 infrared transition have been analyzed within the McCumber theory to yield the peak emission cross-section and figure of merit (FOM) for the amplifier gain. It appears that the glass containing MgO as a modifier is characterized by the largest FOM suggesting that the fluorotellurite matrix with this oxide can be a good novel host for Er3+ ion doping. Finally, we propose a new simple method to calculate the mean transition energy of the McCumber approach as the arithmetic average of the barycenter wavenumbers of absorption and emission spectra.

Optical properties of Er3+-Yb3+ codoped CdF2 single crystals

Er3+ (1%), Yb3+ (4%): CdF2 single crystals with good optical quality are grown by the standard Bridgman method. Absorption, excitation, fluorescence and upconversion spectra are carried out at room temperature. The standard Judd–Ofelt (JO) model is applied to absorption intensities of Er3+ to obtain the three phenomenological intensity parameters by the least square fit procedure. The values obtained are in accordance with those of other fluoride hosts with good root mean square fitting. These JO intensity parameters are then applied to determine the radiative transition probabilities (AJJ′), radiative lifetimes (τrad) and branching ratios (βJJ′) of Er3+ transitions. Green excitation spectrum shows that the Er3+ ions doped CdF2 is preferably excited by 4I15/2 → 4G11/2 (375 nm). The obtained Stokes fluorescence spectrum is characterized by an intense green emission and weak red emission for which we have measured the fluorescence lifetime, the cross-section emission, the gain and the radiative quantum efficiency. Under 980 nm laser excitation, intense red and green upconversion emissions induced by efficient energy transfer between Yb3+ and Er3+ ions were achieved in the investigated matrix via a proposed upconversion process. The spectroscopic data indicate that the studied host may offer visible and infrared laser emission.

Spectroscopy of the Er-doped lithium tetraborate glasses

The electron paramagnetic resonance (EPR), optical absorption, and luminescence (emission and excitation) spectra as well as luminescence kinetics of the Er-doped glasses with Li2B4O7 composition were investigated and analysed. The high optical quality glasses with Li2B4O7:Er composition containing 0.5 and 1.0mol.% Er2O3 were obtained from corresponding polycrystalline compound by standard glass synthesis. The EPR spectroscopy in the 4.2–300K temperature range and optical spectroscopy at 300K show that the Er impurity is incorporated into the network of Li2B4O7 glass as Er3+ (4f11, 4I15/2) ions, exclusively. The local structure of the Er3+ luminescence centres in Li sites of the glass network is proposed. Based on the standard Judd–Ofelt theory the oscillator strength (Pcal) and experimental oscillator strength (Pexp) for observed absorption transitions as well as phenomenological intensity parameters (Ω2, Ω4, Ω6) for Er3+ centres in the Li2B4O7:Er glass containing 1.0mol.% Er2O3 were calculated. Spectroscopic parameters of relevance for laser applications, including emission probabilities of transitions (Wr), branching ratios (β), and radiative lifetime (τrad) have been calculated for main observed emission transitions of the Er3+ centres in Li2B4O7:Er glasses. Experimental and calculated lifetimes were compared and quantum efficiency (η) for green (4S3/2→4I15/2 transition) and infrared (4I13/2→4I15/2 transition) emission bands has been estimated.

Spectroscopic properties of heavily Ho3+-doped barium yttrium fluoride crystals**Project supported by the National Natural Science Foundation of China (Grant No. 61275146), the Research Fund for the Doctoral Program of Higher Education of China (Grant No. 20120002110066), and the Special Program of the Co-construction with Beijing Municipal Government of China (Grant No. 20121000302).

The 30 at.% Ho: BaY2F8 crystals were grown by the Czochralski method, and their spectroscopic properties are analyzed systematically by standard Judd–Ofelt theory. The Judd–Ofelt intensity parameters are estimated to be Ω2 = 6.74 × 10−20 cm2, Ω4 = 1.20 × 10−20 cm2, and Ω6 = 0.66 × 10−20 cm2, and the fluorescence branching ratios and radiative lifetimes for a series of excited state manifolds are also determined. The emission cross sections with our measured infrared luminescence spectra, especially important for 4.1 μm, are calculated to be about 4.37 × 10−21 cm2. The crystal quality is preliminarily tested through a mid-infrared laser emission experiment.

The influence of Pr3+ content on luminescence and optical behavior of TeO2–WO3–PbO–Lu2O3 glass

We have investigated the thermal and spectroscopic properties of Pr3+-doped new tellurite matrix with the molar composition 60%TeO2–27%WO3–10%PbO–3%Lu2O3 (TWPLu). The differential thermal analysis has shown that addition of Lu2O3 to the glass results in an increasing resistance against crystallization. The ellipsometric data have provided a Sellmeier-type dispersion relations of the refractive index of the investigated glasses. The optical absorption edge of the TWPLu matrix has been described within the Urbach approach, while the absorption and fluorescence spectra of the Pr3+-doped TWPLu glasses have been analyzed in terms of the standard Judd–Ofelt theory along with the luminescence decay of the 3P0 and 1D2 levels of the Pr3+ ion. A significant influence of the Pr3+ ion concentration on the photoluminescence intensity as well as on decrease of the lifetimes of both levels has been explained by a non-radiative energy transfer between the ions through cross-relaxation and energy migration processes.

Spectroscopy and Calculations for f-f Transitions of Tb3+ Ions in KY3F10 Nanocrystal.

A modified Judd-Ofelt theory is used in this paper to treat the electric dipole transitions within the 4f8 configuration of Tb3+ by considering the main perturbing components. Through the energy-level calculation and the strandard tensorial analysis, the explicit distances between the 4f7 5d configuration and the 5D4 state and other lower 4f8 energy levels are determined. The rare-earth ion Tb3+ substituted at Y3+ sites in KY3F10 has the site symmetry of C4v. The standard Judd-Ofelt parameters A2(10), A2(30), A4(30), A4(50), A6(50), A4(54) and A6(54) are included in the calculation together with odd-λ parameters A1(10), A3(30), A5(50) and A5(54). The fluorescence branching ratios originating from 5D4 are calculated. Compared with the experimental measurements, the modified model yields better results than the standard Judd-Ofelt theory.

Anomalous decays in Nd3+ doped LaAlO3 single crystal

Luminescence decays of metastable Nd3+:4F3/2 level were measured and studied in wide of 10–300K temperature range and compared with the radiative lifetimes derived from standard Judd–Ofelt theory. Nearly resonant cross-relaxation was found to non-radiatively depopulate the metastable level already in 10K, whereas above 50K increased reabsorption of radiation and thermalization of higher Stark component of the 4F3/2 level occur, which resulted in the Boltzmann population of this metastable Nd3+ level and anomalous increase of luminescence decays with temperature increment.

Concentration-dependent spectroscopic properties of Pr3 + ions in TeO2–WO3–PbO–La2O3 glass

The purpose of this work was to investigate the spectroscopic properties of Pr3+ ions of various concentrations embedded in a new matrix, namely a tellurite–tungstate glass with the molar composition 60%TeO2–27%WO3–10%PbO–3%La2O3 (TWPLa). The optical absorption edge of the TWPLa matrix has been described within the Urbach approach, while the absorption and fluorescence spectra of the Pr3+-doped TWPLa glasses have been analyzed in terms of the standard Judd–Ofelt (J–O) theory along with the luminescence decay of the 3P0 and 1D2 levels of the Pr3+ ion. A significant influence of the Pr3+ ion concentration on the photoluminescence intensity as well as on decrease of the lifetimes of both levels has been explained by a non-radiative energy transfer between the ions through different cross-relaxation channels. The spectroscopic studies have been completed with ellipsometric measurements providing the dispersion relation of the refractive index of the investigated glasses that has been taken into account in the J–O analysis.