V. Lavín

On the local structure of Eu3+ ions in oxyfluoride glasses. Comparison with fluoride and oxide glasses

Broadband and fluorescence line narrowing optical spectroscopic studies have been used to investigate the local environments of Eu3+ ions in lithium fluoroborate glasses. From the vibronic spectra, different borate groups coupled with the Eu3+ ions have been identified. A pulsed tunable dye laser has been used to selectively excite the 5D0 level of the Eu3+ ion and the subsequent 5D0→7F1 fluorescence spectra have been monitored as a function of the exciting wavelength. From these FLN studies, three 7F1 Stark levels have been identified and a C2v orthorhombic symmetry has been assumed in the subsequent calculation of the crystal-field parameters for the different environments occupied by the Eu3+ ions in the glass. The second rank crystal-field parameters have been systematically analyzed for the Eu3+:lithium fluoroborate glass from the site dependent behavior of the 7F1 level splitting. The importance of the J-mixing in the crystal-field analysis has been emphasized. An appropriate method for comparing th...

Optical properties of Er3+ ions in transparent glass ceramics

Abstract A study of optical properties and upconversion processes among Er 3+ ions in oxyfluoride glass and glass ceramic matrix has been carried out. From optical absorption spectra, the oscillator strengths have been obtained for several transitions and they have been used to calculate the Judd–Ofelt parameters. Experimental lifetime values are compared with those obtained with the Judd–Ofelt theory. Different upconversion emissions at 545, 660 and 800 nm have been obtained in Er 3+ doped glass and glass ceramics by exciting at 975 nm. A systematic investigation of the green upconversion is reported with the purpose of determining the involved upconversion mechanisms.

Optical properties of Nd3+ ions in oxyfluoride glasses and glass ceramics comparing different preparation methods

A study of optical properties of Nd3+ doped oxyfluoride glasses and glass ceramics prepared by three different methods has been carried out. These methods start from NdF3, Nd2O3, or a Nd3+ ion solution as doping agent. The alternative preparation method based on a preliminary dissolution of the Nd3+ ions is proposed in order to avoid nonhomogeneous dopant distribution and spontaneous devitrification during glass elaboration. In the frame of the Judd–Ofelt theory, main radiative parameters have been studied: transition probabilities, lifetimes, and stimulated emission cross sections. Fluorescence decay curves have been also analyzed in order to study the final distribution of the Nd3+ ions after the ceramming process, discerning between ions that reside in the fluoride nanocrystals precipitated during heat treatment and those remaining in the glassy phase. The NdF3 based glass ceramics present the best values for spectroscopic parameters as the stimulated cross section of the 4F3/2→4I11/2 laser transition.

Optical spectroscopy analysis of the Eu3+ ions local structure in calcium diborate glasses

Abstract A detailed analysis of the optical properties of Eu3+ ions in calcium diborate glasses has been performed in order to correlate them with the local environment of the lanthanide ions in these glasses. From the excitation and emission spectra under broadband excitation the energy level diagram of the Eu3+ ion and the atomic parameters have been obtained. Moreover, it is found that the Eu3+ ions are predominantly bonded with the bridging and non-bridging oxygens of different borate groups containing the BO3 units. Under site selective excitation in the 7 F 0 → 5 D 0 inhomogeneously broadened peak, valuable information about the splitting of the 7F1 and 7F2 levels and the lifetime of the 5D0 level has been obtained as a function of the excitation wavelength. The linewidth of the low-energy components of the 5 D 0 → 7 F 1 emission shows an increase with the splitting of this level that can be well explained considering non-radiative de-excitation processes towards lower 7F1 Stark levels. From the splitting of the 7F1 and 7F2 levels, the second and fourth rank crystal-field parameters have been calculated as a function of the excitation wavelength. The observed behaviour suggests the existence of an unique class of site for the Eu3+ ions, with a large range of values for the crystal-field strength parameter NV(B2q), from 1000 to 3200 cm−1, that includes weak, medium and strong crystal-field environments for the Eu3+ ions in the calcium diborate glass. The J-mixing is shown to play a relevant role in these calculations for medium and strong crystal-field environments, i.e., for values of the crystal-field strength parameter NV(B2q) over 1400 cm−1.

Optical spectroscopy, 1.5μm emission, and upconversion properties of Er 3+ -doped metaphosphate laser glasses

Metaphosphate glasses doped with five concentrations of Er3+ ions have been investigated through absorption and emission spectra, decay curves, and upconversion measurements. Judd-Ofelt parameters have been evaluated from absorption spectrum of the 1.0mol.%Er3+-doped glass, which are in turn used to predict radiative properties of some important luminescence levels of Er3+ ions in these glasses. Gain bandwidths of an optical amplifier have been evaluated and are compared with those of reported Er3+:glass systems. Temperature dependence of the 1.5μm emission has been studied for the 2.0mol.%Er3+-doped glass from 13K to room temperature. Lifetimes of the I13/24 level were measured and are found to decrease with concentration of Er3+ ions after 0.1mol.%. Concentration quenching of lifetimes has been analyzed using the theory developed by Auzel [J. Lumin.94-95, 293 (2001); Opt. Mater.24, 103 (2003)]. Infrared to visible upconversion was also measured for three concentrations of Er3+-doped metaphosphate glasses with 794nm excitation. A mechanism, involving excited state absorption and energy transfer upconversion, has been proposed to explain the upconversion process.

White light generation in Dy 3+ -doped oxyfluoride glass and transparent glass-ceramics containing CaF 2 nanocrystals

The radiative emission properties of the Dy3+ ions in an oxyfluoride glass and glass-ceramics have been studied for the generation of white light. The x-ray diffraction pattern of the glass-ceramics shows the formation of CaF2 fluorite-type nanocrystals in the glass matrix after a suitable thermal treatment of the precursor glass, whereas time-resolved optical measurements show the incorporation of the Dy3+ ions in the CaF2 nanocrystals. Intense white light has been observed when the samples are excited with 451 nm laser light. From the visible emission spectra, yellow to blue intensity ratios and the chromaticity color coordinates have been determined. All the color coordinates are found to lie in the white light region of the chromaticity color diagram.

Energy transfer with migration. Generalization of the Yokota–Tanimoto model for any kind of multipole interaction

The dynamics of luminescence decay is analyzed within the general scenario of randomly distributed ions with whatever multipole interaction, taking into account energy transfer and migration processes among them. By applying Pade approximants to the Allinger and Blumen expression for the excited state population, a simple expression has been obtained which can be easily fitted to experimental data. This expression can be considered a generalization of the dipole–dipole Yokota–Tanimoto equation. On the other hand, the decay curves from the 5D3 level of the Tb3+ ions in fluorozincate glasses have been measured for different Tb3+ concentrations. The results are analyzed in the framework of the proposed expression.

Spectral investigations on Dy3+-doped transparent oxyfluoride glasses and nanocrystalline glass ceramics

Dysprosium-doped oxyfluoride glasses and nanocrystalline glass ceramics have been synthesized and studied by x-ray diffraction, absorption, and visible and near-infrared emission spectra. The samples emit intense white light when populating the F49/2 level with a 451 nm laser light and, from the visible emission spectra, yellow to blue intensity ratios and chromaticity color coordinates have been calculated and their relative variation have been discussed based on the concentration of Dy3+ ions and the heat treatment conditions used to prepare the glass ceramics. Infrared emission has also been observed in glasses and glass ceramics after laser excitation at 800 nm, showing bands at 1.33 and 1.67 μm, useful for optical amplification in fiber amplifiers.

Stimulated and upconverted emissions of Nd3+ in a transparent oxyfluoride glass-ceramic

Abstract The stimulated emission properties of Nd3+ ions in an oxyfluoride glass-ceramic have been studied. Ultraviolet and visible emissions generated by upconversion processes inside the laser cavity under lasing and non-lasing conditions have been also characterized. The expected losses produced by these processes have been estimated.

Site selective study of Eu3+-doped transparent oxyfluoride glass ceramics

Optical properties of Eu3+ ions in oxyfluoride glasses and glass ceramics doped with two different concentrations, 0.1 and 1 mol %, have been analyzed and compared with previous results for higher concentrated samples, 2.5 mol %. The Eu3+ ions in the 0.1 mol % doped glass ceramics are diluted into like crystalline environments with higher symmetry and lower coupled phonon energy than in the precursor glasses; meanwhile in the 1 mol % doped glass ceramics the presence of EuF3 clusters has been observed in addition to diluted ions. Fluorescence line narrowing measurements indicate the presence of two main fluoride site distributions for the diluted Eu3+ ions in both glass ceramics.