Optical transition probabilities and compositional dependence of Judd–Ofelt parameters of Nd3+ ions in fluoroindate glasses

doi:10.1016/S0022-3093(01)00412-4

Journal of Non-Crystalline Solids

Volume 284, Issues 1–3, May 2001, Pages 261-267

https://doi.org/10.1016/S0022-3093(01)00412-4 Get rights and content

Abstract

Indium fluoride-based glasses constitute a new generation of materials for applications in the mid-infrared range. Fluoroindate glasses with the following compositions (in mol%): (40−x)InF₃, 20ZnF₂, 20SrF₂, 16BaF₂, 2GdF₃, 2NaF, and xNdF₃. with x=1.0,1.5,…,4.0 NdF₃ mol% were prepared in a dry box under argon atmosphere. The absorption spectra at room temperature in the spectral range 300–5000 nm were obtained. The experimental oscillator strengths, f_exp, were calculated from the areas under the absorption bands. Using Judd–Ofelt theory and the fit process of least square, the phenomenological intensity parameters $Ω_{λ}$ (λ=2,4,6) were obtained. From f–f intensity model the theoretical oscillator strengths f_cal are calculated. In order to evaluates potential applications of Nd³⁺ ions in fluoroindate glasses, the spectroscopy parameters: transition probability between multiplets A_JJ^′, branching ratio β_JJ^′, radiative lifetime τ_r, peak cross-section for stimulate emission ρ_p, for each band were obtained. The results were compared with those reported in the literature for similar glasses in the same concentrations and show that $^{4} F_{3/2} →^{4} I_{11/2}$ transition has the most potential for laser application with a peak fluorescence at 1036 nm.

Introduction

There is interest in the study of rare-earth-doped heavy metal fluoride glasses. These materials are transparent from ultraviolet (UV) to the infrared (IR) region; they can be easily prepared and a range of concentrations of transition metal and rare earth can be incorporated into the glass [1].

Besides the well-known zirconate glasses, several compositions based on indium fluoride, called fluoroindates, have been studied [2]. Compared to fluorozirconate glasses, these compositions have greater transparency in the mid-infrared range (up to 8 μm) smaller multiphonon emission rates, chemical stability, and are also more stable against atmospheric moisture [2], [3], [4]. We have recently described several optical properties of Er³⁺, Pr³⁺ and Tm³⁺ ions in such glasses [5], [6], [7], [8], [9], [10], [11].

The Judd–Ofelt theory [12], [13] is used to estimate the probability of forced electric dipole transitions. In this theory of f–f transitions, the so-called intensity parameters, $Ω_{λ}$ , with λ=2, 4 and 6, can be determined experimentally from the measurements of the absorption spectra and refractive index of the host material. From these parameters, several important optical properties, e.g., oscillator strengths, radiative transitions probabilities, branching ratios, spontaneous emission coefficients and peak cross-sections for stimulated emission [14], can be evaluated. In this paper, we have determined these quantities for the Nd³⁺ ion-doped fluoroindate glasses for several Nd³⁺ concentrations. A comparative analysis between fluoride and other glasses in similar concentrations is made.

Section snippets

Glass preparation

The samples used in this study have the following composition (in mol%): (40−x)InF₃, 20ZnF₂, 20SrF₂, 16BaF₂, 2GdF₃, 2NaF, and xNdF₃. The InF₃ and NdF₃ were obtained using the ammonium bifluoride process [2]. An excess of NH₄FHF was added to the desired amount of oxides In₂O₃ and Nd₂O₃, in platinum crucible held at 400°C. To analyze the effect of the concentration on optical properties of Nd³⁺ in fluoroindate glasses the concentration, x, was varied from 1.0 to 4.0 (x: 1.0, 1.5, 2.0, 2.5, 3.0,

Results

The absorption spectra of the Nd³⁺ occur due to the transition from the ground state $^{4} I_{9/2}$ , to various excited states. The excited atoms relax via radiative or multiphonon transitions to the possible upper laser level in a shorter time compared to its radiative lifetime. Fig. 1, Fig. 2 show the absorption spectrum of Nd³⁺ ion in fluoroindate glasses at room temperature for the sample of 3.5 mol% in the spectral range from 300 to 2500 nm and from 2500 to 10,000 nm. The spectrum for each sample

Discussion

The location, intensity and breadth of the absorption bands are determined by interaction of Nd³⁺ ion with local crystalline fields. Each absorption band usually consists of a multiplicity of states. Unlike the local crystal field experienced by Nd³⁺ ion in crystalline hosts, the crystal field at sites in glasses varies from site to site. This distribution of crystal fields results in the inhomogeneous broadening of the absorption spectra of rare earth ions in amorphous media. Owing to this

Conclusions

Our analysis shows that the J–O theory can be employed for predicting the relevant spectroscopic parameters associated with the possible laser transitions. As observed in all the other compositions, the three J–O parameters are ordered as $Ω_{2} <Ω_{4} <Ω_{6}$ . Comparison of the present results with other Nd³⁺-doped glassy hosts shows agreement. From magnitudes of the radiative properties we suggest that $^{4} F_{3/2} →^{4} I_{11/2}$ transition has the most potential for laser application with a peak fluorescence at 1036

Acknowledgements

The authors wish to thank the financial support received for this research from: Colciencias, DIF of Sciences Faculty – UIS, Fundación para la Promoción y Desarrollo de la Ciencia y la Tecnologı́a del Banco de la República, and International Cooperation Program Ecos-Nord, Colombia – Francia.

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The intensity of 4F3/2 → 4I11/2 band increases with increase in Nd3+ ions concentration and quenching has been observed after 1.0 mol % of Nd3+ ions . This quenching is due to the energy transfer process through cross-relaxation process (4F3/2: 4I9/2 → 4I15/2: 4I15/2) as depicted in Fig. 3 [11,18,20,34,40–42]. It can be noted from Fig. 3 that the relative intensity value of 4F3/2 → 4I11/2 emission has become more preferable with respect to 4F3/2 → 4I9/2 transitions with the increase in bismuth content which is also evident from the Ω4/Ω6 magnitudes, estimated from JO parameters.
Trivalent neodymium (Nd³⁺)-doped boro-bismuth glasses have been prepared adopting the high temperature melt and quick quenching procedure and investigated their physical and optical characteristics. Physical properties and their relationship with the composition are demonstrated. Judd-Ofelt parameters have been derived using absorption spectra of Nd³⁺ ions embedded boro-bismuth glasses and are taken to estimate radiative parameters of the fluorescent states of Nd³⁺ ions. The calculated radiative properties, experimental quantities derived from emission spectra and decay curves of the ⁴F_3/2 state provide comprehensive optical properties of the glasses besides their emission capability for the laser activity near 1.06 μm.
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The optical gain parameter (σP × τm), and gain bandwidth (σP × Δλeff) are two important parameters of a laser active medium, which predict the amplification and efficiency of the medium. Larger value of stimulated emission cross-section signifies a good laser active medium with low threshold and high gain factor [33]. In Nd3+ ion for 4F3/2 → 4IJ (J = 9/2, 11/2, 13/2 and 15/2) transition the radiative parameters does not depend on Ω2 since the values of the matrix element of < 4F3/2‖U2‖4IJ > are zero for all these transitions [9].
Spectroscopic investigations on 1 mol% Nd³⁺ embedded xPbO + (100-x) P₂O₅ (where x = 40, 50, and 60 mol %) glasses have been reported. Adopting a free-ion Hamiltonian, the energy values and the free-ion parameters are determined. Judd-Ofelt intensity parameters (Ω₂, Ω₄, Ω₆) of Nd³⁺ ions in lead phosphate glasses are evaluated. Symmetry and covalency of Nd³⁺ ions are studied with increasing PbO contents in the host glasses. Strong emission due to ⁴F_3/2 → ⁴I_11/2 transition at 1055 nm in the near infrared (NIR) region is observed in the glasses upon excitation at 585 nm. Using the Judd-Ofelt intensity parameters, the radiative transition probability (A_R), branching ratio (β_R), radiative decay lifetime (τ_R), stimulated emission cross-section (σ_P), optical gain parameter and gain bandwidth are calculated for the ⁴F_3/2 metastable state of Nd³⁺ ion. The luminescence lifetimes are estimated from the decay profiles. Various luminescence parameters for ⁴F_3/2 → ⁴I_J (J = 9/2, 11/2 and 13/2) transitions are compared with some commercially available Neodymium doped phosphate-based laser glasses. Our investigation indicates that the present glasses could be utilized as the more efficient laser active materials for emission in the NIR region at 1055 nm.
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Influence of Al<inf>2</inf>O<inf>3</inf> on the photoluminescence and optical gain performance of Nd3+ doped germanate and tellurite glasses
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Citation Excerpt :
We recall that when the Nd3+ concentration and the pump power are maintained and the peak wavelength almost does not change, the gain is influenced by the emission cross-section, the measured lifetime, and the effective bandwidth [56]. Therefore, the following parameters σem x Δλeff (figure of merit) and σem x τm (gain bandwidth) are important to evaluate the optical amplification in the medium doped with Nd3+ ions [61,67,74] and are presented in Table 4. The σem x τm parameter represents a figure of merit of the laser transition since longer lifetime allows the required high population inversion to be obtained under modest pump power [56,74]; moreover, it is generally desirable for the emission cross-section to be as large as possible to provide high gain.
We investigated the influence of aluminum oxide, Al₂O₃, on the photoluminescence (PL) spectrum and optical gain (at 1064 m) of neodymium ion, Nd³⁺, doped tellurium and germanium oxide glasses with compositions TeO₂ − ZnO and GeO₂ − PbO, respectively. The PL properties of both materials were studied using a continuous-wave diode laser operating at 808 nm, in resonance with the Nd³⁺ transition ⁴I_9/2 → ⁴F_5/2. For samples containing Al₂O₃ it was observed PL intensity growth up to 30% in comparison with the samples without Al₂O₃. Luminescence decay (τ_m) from the ⁴F_3/2 level was measured monitoring the ⁴F_/32 → ⁴I_11/2 transition. From calculations of the Judd–Ofelt parameters, the radiative lifetimes, the emission cross -section (σ_em) and the quantum efficiency of ⁴F_3/2 → ⁴I_11/2 transition were determined; the effective linewidth (Δ_λeff) was calculated to determine the gain bandwidth product (σ_em x Δ_eff), figure of merit (σ_em x τ_m) and saturation intensity (I_s) parameters. Optical gain measurements were performed using a pump laser at 808 nm and a probe laser at 1064 nm. For the samples with Al₂O₃ the relative gain at 1064 nm reached $\approx$ 2.8 dB/cm (pump laser power: 400 mW) indicating an enhancement of about 65% for TeO₂ − ZnO and 120% for GeO₂ − PbO with respect to the samples without Al₂O₃. The optical gain enhancement is correlated to the PL intensity behavior and increases due to the presence of Al₂O₃ because the coordination environment of the Nd³⁺ changes and become more asymmetric leading to the growth of the emission cross-section. The present study shows that Nd³⁺ doped tellurium and germanium oxide glasses containing Al₂O₃ present particularly good prospects to be used as optical amplifiers at 1064 nm.

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Journal of Non-Crystalline Solids

Abstract

Introduction

Section snippets

Glass preparation

Results

Discussion

Conclusions

Acknowledgements

References (25)

Chem. Phys. Lett.

J. Alloys Compounds

J. Alloys Compounds

J. Non-Cryst. Solids

J. Non-Cryst. Solids

Chemtronics

Electron Lett.

J. Mater. Res.

Phys. Rev. B

IEEE Photonics Technol. Lett.

Cited by (43)

Extension of Judd-Ofelt theory: Application on Eu<sup>3+</sup>, Nd<sup>3+</sup> and Er<sup>3+</sup>

Spectroscopic properties of Nd<sup>3+</sup>-doped boro-bismuth glasses for laser applications

Spectral investigations of Nd<sup>3+</sup>:Ba(PO<inf>3</inf>)<inf>2</inf>+La<inf>2</inf>O<inf>3</inf> glasses for infrared laser gain media applications

Compositional dependence of the luminescence properties of Nd<sup>3+</sup> ions in lead phosphate glasses: The efficient laser active materials

Role of TeO<inf>2</inf> coordination with the BaF<inf>2</inf> and Bi<inf>2</inf>O<inf>3</inf> on structural and emission properties in Nd<sup>3+</sup> doped fluoro phosphate glasses for NIR 1.058 μm laser emission

Influence of Al<inf>2</inf>O<inf>3</inf> on the photoluminescence and optical gain performance of Nd<sup>3+</sup> doped germanate and tellurite glasses