Martin G. Drexhage

Multiphonon relaxation and infrared‐to‐visible conversion of Er3+ and Yb3+ ions in barium‐thorium fluoride glass

The upconversion of infrared radiation into green and red fluorescence has been studied for Er3+ and Yb3+ ions in BaF2/ThF4 fluoride glass over a wide temperature range and several dopant concentrations. At room temperature an upconversion efficiency of 3.3×10−5 has been obtained for the green emission from the glass with 1 mol % ErF3 and 19 mol % YbF3 pumped by 973‐nm radiation with intensity of 16.5 mW/cm2. For an absorbed intensity of 10 W/cm2 the efficiency for green upconversion emission is predicted to be 2%. Radiative transition rates for the excited states of Er3+ were calculated using Judd–Ofelt theory and intensity parameters obtained from measured integrated absorption coefficients. The calculated values of the multiphonon relaxation and the upconversion fluorescence intensity, obtained from the rate equation model of Wright, are discussed in light of the experimental results.

Radiation effects and optical transitions in yb3+ doped barium-thorium fluoride glass

The effect of 1.7 MeV electrons on the coloration of Yb 3+ doped BaF 2 /ThF 4 base fluoride glasses has been investigated. Irradiation at 80 K produces a prominent absorption band at 302 nm. At room temperature, the radiation induced absorption is quite small in these glasses when compared with the absorption in fluorizirconate glasses. The photochemical damage mechanism is dominant. The optical absorption and emission spectra as well as the fluorescence lifetime of Yb 3+ ion transitions have been measured. The measured lifetimes are compared with the calculated radiative lifetimes.

Radiation effects in fluoride glasses

Radiation‐induced defects in Zr‐based fluoride glasses have been characterized using optical absorption and electron spin resonance (ESR) techniques. The optical absorption bands due to interstitial fluorine atoms, the F−2, FCl−, Cl−2 centers, and Zr3+ centers have been identified by correlating optical absorption and ESR measurements. Polarized bleaching experiments indicate that the hole‐type centers, and the Zr3+ centers have anisotropic defect configurations. X‐ray excitation at 14 K generates a broad, asymmetric emission band at 337 nm (3.68 eV), which is assigned to a localized‐excited state similar to that for self‐trapped excitons in halide crystals. The intensity of the x‐ray induced emission provides further evidence that radiolysis defect production occurs in this material. The optical tail of the radiation‐induced Zr3+ absorption affects infrared transmission. Evidence is presented that the CCl4 reactive‐atmosphere process introduces a significant amount of Cl− (∼5%) in the glass.

Vibrational spectra of fluorohafnate glass

Abstract We report the first detailed measurements of fundamental vibrational spectra in fluorohafnate glass. The Raman spectrum is dominated by a single relatively broad peak in the vicinity of 570–590 cm −1 attributed to Hf-F stretching modes, while the infrared spectrum displays two prominent broad peaks. The location of the high frequency peaks is shown to be consistent with the observed position of the infrared absorption edge.

Infrared absorption in highly transparent fluorozirconate glass

Detailed measurements of the frequency and temperature dependence of absorption are reported for the highly transparent frequency regime of a promising new infrared glass based on zirconium fluoride. The results are interpreted in terms of intrinsic multiphonon processes.

Comparative study of BaF2/ThF4 glasses containing YF3, YbF3 and LuF3

Abstract A series of glasses of composition (mol %) (x)BaF 2 − (33.3−x/3)ZnF 2 − (33.3−x/3) − (33.3−x/3)ThF 4 , where M = Y or Yb and x = 10–25 were synthesized. Optical, thermal and microhardness measurements were made and the data compared with that for fluorozirconate, fluorohafnate, and glasses where M = Lu. The subject materials have higher glass transition and crystallization temperatures, higher hardness and somewhat lower UV absorption coefficients than typical ZrF 4 /HfF 4 -based glasses.

Prospective Vitreous Materials For Infrared Fiber Optics

Fiber optics operating in the mid-infrared (IR) offer the potential for lower losses and better tolerance to nuclear radiation than current silicate-based fibers. Moreover, mid-IR fibers may be useful for a variety of shorter distance applications such as laser surgery, spot welding, and infrared integrated optics. Although a wide array of potentially highly transmissive mid-IR materials are available in bulk form, most are not suitable for fiber fabrication. Recently, however, a variety of new multicomponent glasses based on the fluorides of heavy metals have been developed, which may offer the best prospects to date for high performance mid-IR fibers. A critical comparison of the advantages as well as the problems associated with various prospective materials and fiber fabrication techniques is given.

Crystallization And Viscosity Of Heavy Metal Fluoride Glasses

Shear viscosity data for a glassforming ZrF4-BaF2-LaF3-A1F3 composition covering the range from the highly fluid melt down to the glass transition (10-1 to 1013 P) have been collected from five sources. The viscosity temperature dependence is highly non-Arrhenius and cannot be described by three parameter expressions such as the Fulcher equation. The four parameter Cohen-Grest equation, however, does give a good fit to the data, possibly allowing interpolation in the range of intermediate viscosity important for fiber drawing where data is currently lacking. The viscosity data are compared with crystallization temperatures obtained by DSC during heating and cooling at 10K/min.

Paramagnetism in heavy metal fluoride glasses

Abstract The preparation and characterization of heavy metal fluoride glasses in the system BaF2MnF2ThF4 (BMT) are discussed. Rare earth ions, Eu, Gd, Tb, Dy, Ho, Er, Tm, and Yb are incorporated in BMT composition to study the effect of these ions on the magnetic and magneto-optic properties of the base glass. Glass transition and crystallization temperatures (Tg and Tx) are determined. The measured glass samples have low Verdet constant, exhibit strong paramagnetic behavior and are transparent in the infrared spectral region (2–9 μm).

Viscosity Temperature Dependence and Crystallization of Heavy Metal Fluoride Classes

The temperature dependence of the viscosity of heavy metal fluoride glasses is important for determining processing temperatures for procedures such as fiber drawing and in understanding crystallization behavior in these systems. Viscosity data in the glass transition region and in the liquid region have been measured by several different laboratories for ZBLA (58 ZrF 4 -33 BaF 2 -5 LaF 3 -4 AlF 3 ) and ZBLAN viscosity-temperature curves for these two compositions are highly non-Arrhenius in nature, and cannot be described by the Fulcher equation; however the Cohen-Crest equation fits the data very well. On a reduced temperature scale (T g /T), the viscosity curves nearly coincide, suggesting the possibility of a master viscosity equation for fluorozicronate glasses. Crystallization temperatures for these compositions have been measured by differential scanning calorimetry. On reheating, the first crystallization product for both compositions is a barium fluorozicronate phase. However, ZBLAN glass does not crystallize until a much lower viscosity is reached, compared to ZBLA. These results indicate that the devitrification behavior for ZBLAN is due to additional entropy of mixing from the addition of NaF.