J. Javorniczky

Fluorescence from highly-doped erbium fluorozirconate glasses pumped at 800 nm

Abstract A study of the fluorescence properties, under 800 nm excitation, of new ZBEAN glasses with Er 3+ concentrations up to 18 mol% is reported. This represents the highest reported doping concentration for this type of glass. The fluorescence intensity at 550 nm, 1.53 μm and 2.7 μm did not exhibit the expected strong quenching at these high concentrations and the corresponding decay times were consistent with this observation. Cooperative energy transfer between the relevant levels is discussed as a possible explanation of this behaviour.

Faraday rotation in rare earth fluorozirconate glasses

Abstract The Verdet constants of a number of fluorozirconate glasses, containing substantial mole fractions of rare-earth ions, have been obtained. The Verdet constants measured were principally of paramagnetic origin and were found to be well described by the Van Vleck–Hebb equation, as a function of wavelength between 365 and 589 nm. The effective transition wavelengths, and the value of V at 633 nm, were extracted from fits to the Van Vleck–Hebb equation. These were found, for any given rare-earth ion, to be independent of concentration, within the uncertainty of the data. The effective transition wavelengths in the fluorides were significantly (approx. 30–50 nm) less than those observed in comparable rare-earth doped oxide glasses. This indicated that the fluoride matrix was a factor in determining the overall effective transition energy and thereby the size of the effect at any given wavelength. Comparison of the effect exhibited by glasses containing one of Dy, Pr, Tb or Ce showed that the size of the Verdet constant was only approximately correlated with the 4f→5d transition energy of the free rare-earth ion. Of these rare-earths, Tb generated the largest Verdet constants for a given concentration of active species.

High Er(III) content ZBN glasses for microchip laser applications

Abstract The preparation and properties of zirconium/barium/sodium fluoride glasses containing high Er(III) contents are discussed in detail. Glasses containing up to 33×10 20 Er(III) cm −3 (18 mol%) have 1530 nm fluorescence lifetimes in the region of 10 ms and show no evidence of concentration quenching in their emission at various wavelengths in the infra-red. The lack of substantial concentration quenching was an unexpected result and possible reasons for this are discussed.

Systematic study of refractive index variations with composition in heavy metal fluoride glasses

Abstract In order to further understand the dependence of the refractive index on composition, a systematic investigation of the relationship between these quantities has been undertaken. Starting with well known stable quinary glass compositions containing zirconium tetrafluoride, the effects of dopants such as alkali ions and PbF2 on the refractive index have been investigated. In addition, thermal analysis was carried out to ascertain the extent to which glass stability had been affected by the compositional changes. A refractive index difference, Δn, of up to 0.02 and numerical aperture (NA) of 0.23 was obtained at compositions for which the difference in glass transition temperature, ΔTg, was only 1°C. The molar refractivity for stable glass systems showed a good correlation with theoretically predicted results, except for systems containing LiF.

High erbium content heavy metal fluoride glasses

Abstract Rare earth glasses with high doping concentrations are candidates for the production of eye-safe microchip lasers for use as transmitters and detector amplifiers in laser radar systems and as transmitters in ultrahigh data rate communication systems. Presently only low concentrations of rare earths have been incorporated into glass hosts but microchip lasers will require higher dopant concentrations in order to obtain sufficient absorption of the pump radiation. In this work, glass systems based on ZrF4 were found to be able to support dopant concentrations of ErF3 up to 18 mol%. The thermal, optical and absorption properties of these ZBEAN glasses are examined as a function of concentration.

Energy exchange processes in Er3+-doped fluorozirconate glasses

Abstract 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 Er3+-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 Er3+ 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.

Electrochemical studies of rare earths in fluoride melts

Liquid electrochemical methods were used to generate the cyclic voltammograms of Sm(III), Yb(III) and Eu(III) in glass forming fluorozirconate and fluoroaluminate liquids. All three species were observed to undergo reduction within the window of stability of the liquids. In all cases we hypothesized that it is the M(II) state that is generated. The redox processes observed were found to be close to reversible at smaller scan rates, becoming quasi-reversible at larger scan rates.

Enhanced fluorescence from nano-crystallized erbium-doped fluoroaluminate glasses

Abstract A fluoroaluminate glass containing 30 mol% ErF 3 has been subjected to controlled nucleation and crystal growth. The resultant material is transparent but has a fraction of crystallinity as discernible by differential scanning calorimetry and X-ray diffraction. The size of the crystals was determined by small-angle X-ray scattering to be approximately 8–12 nm. Er 3+ fluorescence intensity at 1550 nm as a result of 800 nm pumping was approximately 40% greater than in the case of the base glass.

Heavy metal fluoride glasses studied by positron annihilation lifetime spectroscopy. I. Comparison of 53ZrF4·(40−x)BaF2·4LaF3·3AlF3·xLiF and 53ZrF4·20BaF2·4LaF3·3AlF3·(20−xCsF·xLiF☆

Abstract Heavy metal fluoride glasses of varying alkali metal fluorides have been studied by positron annihilation lifetime spectroscopy. The alkali series 53ZrF4·(40−x)BaF2·4LaF3·3AlF3·xLiF is compared with the mixed alkali series 53ZrF4·20BaF2·4LaF3·(20−x)CsF·xLiF. The mean lifetime and refractive index are non-linear functions of the dopant concentration, (40−x)BaF2·xLiF, in the alkali series as compared with the linear dependence of the mean lifetime and refractive index on the dopant concentration, (20−x)CsF·xLiF, found in the mixed alkali series. The alkali series spectra can be best fitted by a single lifetime, while the mixed alkali series spectra can be best fitted with two lifetime components. Probable states of the positron at annihilation in these glasses are discussed and compared with those states found in oxide glasses. There is no evidence for ortho-positronium annihilation in these fluoride glasses.

High numerical aperture heavy metal fluoride glass combinations for single-mode optical fibres

The core-cladding composition difference is a crucial element in the design of high numerical apertures for single-mode fluoride glass optical fibres. The larger the numerical aperture, the more light that can be launched into the fibre core. Starting with well known stable glass compositions containing zirconium fluoride, PbF 2 , LiF and GaF 3 have been introduced into the core and cladding respectively to increase the difference in refractive index, Δn, and thus increase the numerical aperture, while still maintaining a high degree of stability. A refractive index difference, Δn, of 0.06 and numerical aperture of 0.41 was obtained for compositions (ZrF 4 -BaF 2 -LaF 3 -AlF 3 -LiF-PbF 2 (ZBLALiPb3) for the core and ZrF 4 -BaF 2 -LaF 3 -AlF 3 -NaF-GaF 3 (ZBLNGa13) for the cladding), where the difference in the glass transition temperature, T g , was only 4°C. The relationship between the differences in refractive index, Δn, and glass transition temperature, ΔT g , with compositional changes of the glass host are discussed