Doped Fluorozirconate Glasses Research Articles

An investigation of 3.5 μm emission in Er3+-doped fluorozirconate glasses under 638 nm laser excitation

An investigation of 3.5 μm emission in Er3+-doped fluorozirconate glasses under 638 nm laser excitation

Luminescence of Fluorochlorozirconate Glasses Doped with Manganese Ions

A series of fluorochlorozirconate glasses doped with manganese ions is synthesized and investigated as possible red‐emitting phosphors in comparison with conventional green‐emitting fluorozirconate glasses doped with Mn2+. It is found that the replacement of fluorine by chlorine ions results in broadening and a long‐wavelength shift of the manganese luminescence band into the red region (peaked at 615 nm) although the emission spectrum still has some contribution of the green sub‐band. It turns out also that decay kinetics of luminescence from fluorochlorozirconate glasses becomes nonexponential in contrast to single‐exponential decay observed for green luminescence from Mn2+‐doped fluorozirconate glasses. The observation of two emission components in the luminescence spectrum of fluorochlorozirconate glasses is interpreted as being due to the presence of two Mn2+ emission centers in different local environments. The presence of 2+ valence states of manganese ions in both types of glasses is confirmed by recording X‐ray absorption near edge structure (XANES) spectra at Mn L2,3 edge. Substitution of F− by Cl− ions in anion sites neighboring to Mn2+, leads to a significant rearrangement of the local environment of Mn2+ ions, which results in the long‐wavelength shift of Mn2+ emission spectrum.

Glass-forming ability control of Er3+-Doped lithium-modified fluorozirconate glass

The glass-forming ability of Er3+-doped fluorozirconate glasses was systematically investigated by replacing Na+ ions by Li+ ions. As Li+ content increased, the glass-forming ability showed an approximate Gaussian distribution, and an optimal thermal stability was obtained with the dopant of 5 mol% Li+. The mechanism for the enhancement of glass-forming ability in fluoride glasses upon partial substitution of Li+ ions was preliminarily investigated. Moreover, an Er3+-doped fluorozirconate glass modified by 5 mol% Li+ exhibited stronger fluorescence than the unmodified original glass. The results provided a suitable approach for fluoride glass modification.

Low phonon energy BaCl2 nanocrystals in Nd3+-doped fluorozirconate glasses and their influence on the photoluminescence properties

ABSTRACTNd3+-doped fluorozirconate glasses, which were additionally doped with chlorine ions, were investigated for their photoluminescence (PL) properties. Upon heat treatment of the as-made glass, hexagonal phase BaCl2 nanocrystals are formed within the material, which undergo a phase transformation to orthorhombic BaCl2 upon annealing at a higher temperature. The glasses with hexagonal phase BaCl2 nanocrystals show an enhanced Nd3+ PL in the visible spectral range. Time-resolved spectroscopy on the 4G5/2 / 2G7/2 → 4I9/2 transition shows that the existence of hexagonal BaCl2 nanocrystals results in a significantly longer decay time. The temperature dependence of the lifetime yielded that the enhanced PL is due to a reduced multi-phonon relaxation rate.

Mechanical properties of fluorozirconate-based glass ceramics for medical and photovoltaic applications

Young's and shear moduli were analyzed in Eu 2+-doped fluorozirconate glasses, which were additionally doped with chlorine ions. Upon annealing between 240 °C and 290 °C, barium chloride nanocrystals were formed in the glass. Determination of the Vickers hardness, H, leads to a slight trend of decreasing hardness for higher annealing temperatures, whereas subsequent annealing has almost no effect on the fracture toughness K Ic.

Structural and optical investigations of Nd-doped fluorozirconate-based glass ceramics for enhanced upconverted fluorescence

We found enhanced upconverted fluorescence in Nd3+-doped fluorozirconate glasses which were additionally doped with chlorine ions. Upon annealing between 240 and 290°C, hexagonal phase BaCl2 nanocrystals between 20 and 180nm in diameter were formed in the glass. During the thermal processing, some of the Nd3+ ions enter the nanocrystals leading to additional splitting of the infrared fluorescence spectra and to increased upconverted fluorescence intensities. The optimum value was found for the 270°C sample where the upconverted fluorescence intensity is approximately a factor of 60 stronger than the one found for the as-made glass.

Infrared-to-visible photon avalanche upconversion dynamics in Ho3+-doped fluorozirconate glasses at room temperature

Abstract Blue, green and red emissions have been generated at room temperature by upconversion processes under infrared laser excitation at 750 and 840 nm in fluorozirconate glasses doped with Ho 3+ ions. The intense green emission, associated to the 5 S 2 , 5 F 4 → 5 I 8 transitions, has been carefully analysed in order to elucidate the mechanisms involved in the energy conversion process. The temporal dynamics of the emission intensities, the extremely weak ground state absorptions, the strong excited state absorptions and the different cross-relaxation processes indicate that two different photon avalanche mechanisms are responsible of the 750 and 840 nm laser-induced upconversion processes in the Ho 3+ -doped fluorozirconate glass.

New developments in X-ray storage phosphors

We found a significant PSL effect in Eu2+-doped fluorozirconate glasses (ZBLAN) which were additionally doped with Br− or Cl− ions. The PSL is attributed to the characteristic emission of Eu2+ present in nano-crystallites of BaBr2 or BaCl2, which form in the glass upon annealing. The metastable hexagonal form of BaX2(X=Br,Cl) is always formed first before it is converted into the stable orthorhombic form. The particle size increases upon annealing and so does the PSL efficiency of the glass ceramic. However, there is a saturation of the PSL efficiency, which is for Br− doping about 9% and for Cl−-doping about 80% of the Eu-doped BaFBr standard. The particle size was determined by transmission electron microscopy (TEM). The TEM results show a clear tendency for bigger particles for longer annealing at the expense of its number. The particle size for the most efficient phosphor is about 100nm.

Laser cooling using anti-stokes fluorescence in Yb3+-doped fluorozirconate glasses

The fluorozirconate glasses ZBLANP (ZrF4−BaF2−LaF3−NaF−PbF2) doped with different Yb3+ concentration were prepared. The Raman spectra and absorption spectra are measured to substantiate the existence of phonon-assisted emission. After analyzing the normalized absorption spectra of samples with different Yb3+-doped concentration, we calculated the maximum cooling effect in the 3 wt% Yb3+-doped sample pumped at 1 012.5 nm. The corresponding cooling capability is about −4.09 °C/W and the cooling efficiency reaches 1.76%.

Simulation of optical spectra of Eu3+ ion in fluorozirconate glasses by molecular dynamics simulation and point charge crystal field

Eu 3+ -doped fluorozirconate glasses with two compositions Zr:Ba=1:1(ZB11) and Zr:Ba =3:1(ZB31) were prepared. The emission, excitation, and fluorescence line narrowing spectra of those glasses were measured. Certain differences between the two glasses were observed in the observed spectra. Structural models of the glasses were simulated by molecular dynamics (MD) simulation. The optical spectra of Eu3+ in those glasses were simulated from the simulated glass structures using a point charge crystal field. The differences in spectral characteristics between the two glasses in the observed spectra were reproduced in the simulated spectra. The MD simulation showed that the barium ions were more apt to coordinate to EuFa clusters than the zirconium ions were.

Comparison between the calculated and measured energy transfer rates of the S3/24 state in Er3+-doped fluorozirconate glasses

The dependence of the fluorescence lifetime of the S3/24 state of the Er3+ ion on the ErF3 concentration was measured in fluorozirconate glasses at room temperature. Energy transfer rates were calculated from optical parameters assuming that the Er3+ ions in fluorozirconate glasses were dispersed as the cubic, bcc, or fcc structure, and were inserted into the rate equation. The dependence of the total transition rate of the S3/24 state of the Er3+ ion on the ErF3 concentration was calculated by using the rate equation and compared with the total transition rate measured by the lifetime experiment. Although many studies have reported the energy transfer rates in various rare-earth ions, the reliability of the calculated energy transfer rates has been hardly discussed. The energy transfer rate can be derived from the total transition rate. The energy transfer rate estimated from the rate equation calculation was compared with the energy transfer rate obtained from the lifetime measurement. It could be shown that the calculated energy transfer rate assuming that the Er3+ ions were dispersed as the cubic structure was closer to the measured energy transfer rate than that as the bcc and fcc structures. With increasing the ErF3 concentration, the calculated energy transfer rate when the Er3+ ions were dispersed as the cubic structure was comparable to the measured energy transfer rate. It was suggested that at the lower concentration of ErF3 (⩽2 mol %), we needed to use the distance between Er3+ ions which was shorter than that as the cubic structure in the calculation of the energy transfer rate.

Energy exchange processes in Er 3+-doped fluorozirconate glasses

A comprehensive study has been conducted on the effects of erbium dopant concentration on the fluorescence properties of the three lowest energy levels which are involved in infrared emission in Er 3+-doped fluorozirconate glass compositions. Pulsed pump radiation at wavelengths of 800 nm, 980 nm and 1.5 μm was used to measure fluorescence rise and decay waveforms for Er 3+ concentrations between 0.2 and 18 mol%. A rate-equation model has been developed for the relevant levels and the fitting of this model to the experimental results has enabled the contribution of various ion–ion energy exchange processes to be identified and quantified. These processes determine, in part, the population dynamics, especially for the larger dopant concentrations used.

Spectroscopy of rare earth ions in fluoride glasses for laser applications

Optical properties of Eu 3+ 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 Eu 3+ ions. As a result, precise information about the local environment of the Eu 3+ ions in the two families of fluoride glasses is obtained.

Upconversion mechanism in Er3+-doped fluorozirconate glasses under 800 nm excitation

The upconversion emission intensities of Er3+ ion around 550 and 660 nm in fluorozirconate glasses were measured under 800 nm excitation. Though energy transfer processes played an important role in upconversion mechanism at high concentration of ErF3, those have not been treated quantitatively. The energy transfer rates were calculated from the optical parameters assuming some distribution of Er3+ ions. We calculated the upconversion intensities around 550 and 660 nm by using rate equations. It was found that the dependence of upconversion emission intensities on the ErF3 concentration could be reproducible and the principal upconversion mechanism could be evaluated.

Effects of impurities on dielectric properties of fluorozirconate glasses at microwave frequencies

The dielectric properties of fluorozirconate glasses doped with different impurities have been investigated in the frequency region of 3.0–12.5 GHz using a microwave network analyzer. For glasses containing oxide impurities such as PbO, SiO2, and TiO2, the position of the dielectric resonance, which is observed in the pure fluoride glass, shifts to higher frequencies. Amplitudes of the resonance peaks also become much smaller. The oxide impurities are observed to exist as large numbers of tiny precipitates in the glasses. When the glasses are doped with InF3, the position of the resonance peak shifts to a higher frequency but the amplitude of the peak remains unchanged. The InF3 may be substituted for AlF3 in the glasses. A higher half-resonance width is observed in the doped fluorozirconate glasses. The changes in the dielectric properties are attributed to the different behaviors of the impurities, which affect the structural interunit vibration in the fluoride glasses.

Site selective study in Eu 3+-doped fluorozirconate glasses and glass-ceramics

Eu 3+ in fluorozirconate glasses and glass-ceramics has been studied by fluorescence line narrowing (FLN). In glasses, the excitation spectrum of the 5D 0 level shows an inhomogeneous electronic peak with a phonon side band (PSB). The effect of the PSB in the narrowed emission spectra is analyzed. By a comparison of the spectra of devitrified glasses and data of EuZrF 7 crystal, it has been possible to our knowledge for the first time to obtain, precise information about the coordination environment of the Eu 3+ ions in a glass matrix.

UV upconversion luminescence of Nd 3+ and Er 3+ ions in fluorozirconate glasses

Upconversion luminescence in the near UV region has been obtained in Nd 3+ and Er 3+ doped fluorozirconate glasses, under argon ion laser excitation for the first time. The intensity of the upconversion luminescence increased with an increase in pumping intensity and dopant concentration. The upconversion transition processes are described, and their mechanisms are also examined.

Up-conversion Luminescence in Er 3+- and Yb 3+-doped Fluorozirconate Glasses

Intense luminescence with up-conversion has been studied for E r3+- and Yb 3+-doped fluorozirconate glasses (ZBLAN). Effective infrared-to-visible conversion has investigated by pumping the glasses with radiation of InGaAs quantum well semiconductor laser at 980 nm. Luminescence has been observed in green (515-550 nm) for Er 3+-doped ZBLAN glasses. Intra- and intercenter processes and low efficient intracenter multiphonon interlevel relaxations were considered as mechanisms involved in the upconversion.

Synthesis and microstructural studies of Er 3+-doped fluorozirconate devitrified glasses

Microcrystallite growth in Er 3+-doped fluorozirconate glasses has been studied by several techniques: extended X-ray absorption fine structure at the erbium L III absorption edge, diffraction (X-ray and electron), fluorescence (optical and X-ray) and electron microscopy. The results of the different techniques are presented and discussed.

Time-resolved spectroscopy of Ni-doped fluorozirconate glasses

Optical absorption, time-resolved luminescence and fluorescence decay measurements of Ni2+-doped fluorozirconate glasses are reported. Time-resolved luminescence measurements have been taken exciting the samples at different wavelengths. The position of the green emission abnd (the 1T2g(D→3A2g(F) transition) moves slightly to the blue when the excitation is changed to higher energies. For a fixed excitation wavelength, the emission moves also to the blue when the time of measurement after the laser pulse increases. The fluorescence decays are non-exponential and depend on the detection wavelength. They are slower for the shorter detection wavelengths. The results show a distribution of Ni2+ sites with different ‘crystal field’ environments.