David Bunimovich

The luminescence properties of Dy-doped high silicate glass

Abstract The visible luminescence of silicate glass (SiO2 (> 70%)—R2O3[B2O3, Al2O3]—RO[ZnO, MgO, CaO, BaO]—R2O[Na2O, K2O]) doped with various concentrations of dysprosium was investigated. The emission, excitation and absorption spectra, as well as kinetic parameters, were measured over a temperature range from 20 to 300 K. The Judd—Ofelt analysis was applied to the data, in order to calculate transition rates and branching ratios for all observed emission bands. Concentration quenching was experimentally observed at a Dy ion concentration higher than 8 × 1019 cm−3 and explained by an analytical model based on the Inokuti-Hirayama theory. The quantum efficiency of visible luminescence and the stimulated emission cross-section at 570 nm were (85 ± 50% and (3.4 ± 0.4) × 10−21 cm2, respectively.

Optical properties of mixed silver halide crystals and fibers

The dependence of the bulk (βb) and surface (βs) absorption coefficients of AgClxBr1−x crystals and of polycrystalline fibers at 10.6 μm on the composition (x) of the material were investigated. The bulk coefficient βb for AgBr was about 0.5×10−4 cm−1 and increased gradually with increasing molar concentration x of the Cl− ions up to 2.5×10−4 for pure AgCl crystals. Luminescence properties of these crystals as well as effects of thermal treatments on the absorption, luminescence, and conductivity were also investigated. A correlation was found between the effects of these treatments on the infrared (IR) absorption, the luminescence, and conductivity of the various samples. Experimental results indicate that the absorption of the silver halide crystals at 10.6 μm is mainly due to cation vacancies bound to dislocations. The absorption of the fibers was found to be greater than that of the crystals of the same composition. This is apparently due to defects induced by the heating under pressure, applied durin...

Fiber-optic evanescent-wave spectroscopy for fast multicomponent analysis of human blood

A spectral analysis of human blood serum was undertaken by fiber-optic evanescent-wave spectroscopy (FEWS) by the use of a Fourier-transform infrared spectrometer. A special cell for the FEWS measurements was designed and built that incorporates an IR-transmitting silver halide fiber and a means for introducing the blood-serum sample. Further improvements in analysis were obtained by the adoption of multivariate calibration techniques that are already used in clinical chemistry. The partial least-squares algorithm was used to calculate the concentrations of cholesterol, total protein, urea, and uric acid in human blood serum. The estimated prediction errors obtained (in percent from the average value) were 6% for total protein, 15% for cholesterol, 30% for urea, and 30% for uric acid. These results were compared with another independent prediction method that used a neural-network model. This model yielded estimated prediction errors of 8.8% for total protein, 25% for cholesterol, and 21% for uric acid.

Dielectric properties of silver halide and potassium halide crystals.

The refractive indices of mixed AgCl(x)Br(1-x) crystals, with x ranging from 0 to 1, are measured at three wavelengths: 0.6328, 2.94, and 10.6 microm. A nonlinear dependence of the refractive index on composition is observed and explained on the basis of a simple Lorentz-Lorenz classical approximation. The theoretical dependence of the static dielectric constant on composition is also calculated. The same calculation is applied to KCl(x)Br(1-x) crystals, and, in both crystal systems, good agreement with experiment is obtained.

Evanescent-wave infrared spectroscopy of solid materials using deformable silver-halide optical fibers

Silver-halide crystalline infrared optical fibers are used for infrared evanescent-wave spectroscopy of solid materials. The fiber is pressed onto the material to be studied and good contact is achieved either by elastic or plastic deformation of the ductile fiber. The absorption-signal level is determined by the length and pressure of contact. This method allows convenient measurement of the absorption signals in large samples that cannot be introduced into an IR spectrometer and in materials that are practically opaque so that their spectra cannot be obtained by conventional transmission measurements. Examples of measurements of hard polymers are given, and the evanescent-wave spectra of polyethylene are compared with conventional transmission measurements.

Absorption measurements of mixed silver halide crystals and fibers by laser calorimetry.

The absorption coefficients of mixed silver halide crystals and fibers were measured by different laser calorimetric methods: adiabatic for crystals and isothermal for fibers. The composition dependence of the bulk absorption coefficients β(b) of crystals and polycrystalline fibers at 10.6-µm (CO(2) radiation) was investigated. It was found that the crystal surface absorption β(s) is dependent on the surface polishing quality. All experimental results of β(b) are smaller than those reported in the literature.

Effects of thermal treatment on the infrared transmission of polycrystalline silver halide fibers

Polycrystalline silver halide fibers were thermally treated by a variety of heating and quenching procedures. For each procedure, the recrystallization process and the grain-size distribution were investigated. The absorption and scattering coefficients at 10.6 mum and the infrared transmittance spectra in the 3-20 mum wavelength range were also measured. Treatment at temperatures above 170 degrees C and long time intervals generally lead to an increase in grain size, with a dependent increase in absorption and scattering coefficients at 10.6 mum. Heating only to temperatures below 170 degrees C reduced the absorptive and scattering losses. The Rayleigh-Gans scattering model was utilized to describe the scattering behavior. A model involving cation vacancies localized at charged dislocations or casual divalent impurities is suggested to explain the infrared absorption of the fibers.

Infrared luminescence of neodymium-doped silver bromide crystals

The infrared luminescence of neodymium-doped silver bromide crystals at 880, 1060, and 1300 nm was investigated. The emission, excitation, and absorption spectra were measured at low and room temperatures. Differences in the temperature dependence of the intensity and in the decay times for different emission bands were observed.

IR luminescence of Ni-doped silver bromide crystals

Abstract The infrared luminescence of nickel-doped silver bromide crystals at 5405 cm −1 (1.85 μm) was investigated. The emission, excitation and absorption spectra were measured at low temperatures. An energy level scheme of the luminescence centers is proposed and some characteristic parameters are estimated.

Absorption spectrum of silver bromide crystals and fibers in the 9–11 μm wavelength range

The absorption spectrum in the 9–11 μm range of both undeformed and plastically deformed AgBr crystals and polycrystalline optical fibers was investigated by tunable laser calorimetry. The observed spectral features are discussed in terms of the crystal defect structure.