U.R. Rodríguez-Mendoza

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.

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.

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.

Role of the Eu3+ ions in the formation of transparent oxyfluoride glass ceramics

Optical properties of Eu3+ ions in oxyfluoride glass ceramics and in the precursor glasses (30 SiO2, 15 Al2O3, 29 CdF2, 22 PbF2, 1.5 YF3, and 2.5 EuF3, in mol %) have been analyzed and compared. The Eu3+ ions in the glass ceramics are incorporated into a crystalline environment with higher symmetry and lower energy coupled phonons. Emission measurements indicate that this crystalline phase is EuF3, instead of PbxCd1−xF2 as generally considered.

Upconversion dynamics in Yb3+-Ho3+ doped fluoroindate glasses

Abstract The mechanisms and dynamics of the upconversion emissions in Yb 3+ –Ho 3+ -doped fluoroindate glasses by exciting at 975 nm have been analysed. The upconversion efficiencies have been measured as a function of temperature in the range from 12 to 295 K. The temporal evolution of the 545- and 650-nm upconversion emissions obtained under flash excitation at 975 nm in codoped samples with 2.25 mol.% of Yb 3+ and 0.75 mol.% of Ho 3+ cannot be described using the energy migration model. This indicates that at this concentration of Yb 3+ the rapid migration regimen between these ions has not been reached. A model is proposed in order to explain the temporal evolution of these emissions taking into account energy migration between donors and backtransfer processes.

Spectroscopy of rare earth ions in fluoride glasses for laser applications

Abstract Optical properties of Eu3+ doped fluorozirconate and fluoroindate glasses have been studied by site selective spectroscopy. From emission spectra and lifetime measurements, Judd–Ofelt parameters and crystal field intensity have been calculated for the different sites occupied by the Eu3+ ions. As a result, precise information about the local environment of the Eu3+ ions in the two families of fluoride glasses is obtained.

Infrared, blue and ultraviolet upconversion emissions in Yb3+–Tm3+-doped fluoroindate glasses

Abstract Intense ultraviolet (362.5 nm), blue (479 nm) and IR (800 nm) upconversion emissions were obtained in fluoroindate glasses co-doped with Yb3+ and Tm3+ ions pumped at 975 nm. The dependence of these upconversion emissions on excitation intensity has been studied and it is concluded that emissions come from Tm3+ ions excited by successive energy transfers from Yb3+ ions. The temporal evolution of the 800 nm upconversion emission obtained under flash excitation at 975 nm cannot be described using the energy migration model. This indicates that at this concentration of Yb3+, the rapid migration regime among these ions has not been reached. A model is proposed in order to explain the temporal evolution of this emission, taking into account back-transfer processes from Tm3+ to Yb3+ ions.