Dimitrij Lezal

Heavy metal oxide glasses: preparation and physical properties

Abstract Heavy metal oxide glasses have been investigated in the following systems: TeO2–PbO–PbCl2, TeO2–ZnO, Ga2O3–PbO–Bi2O3 glasses with low OH concentration were prepared. The influence of the processing conditions on the color, the structure and the optical properties of the prepared samples was also assessed. Mixtures of starting oxides were melted in various reactive conditions using Pt, Au, SiO2 and alumina crucibles. A set of physical measurements including chemical and X-ray analysis, scanning electron microscopy, absorption spectroscopy, ultraviolet and infrared absorption edges and thermo-physical properties, were carried out. Samples were doped with Nd, Pr and Er rare earth ions. Low temperature photoluminescence spectra show the expected rare earth transitions and the broad band emission of the base glass.

GeO2-PbO glassy system for infrared fibers for delivery of Er:YAG laser energy

Abstract Glasses based on GeO2 for optoelectronics application are studied. Attention is focused on the preparation of glasses of various compositions of the GeO2-PbO system under a reactive atmosphere for removing hydride impurities. The optical properties, such as infrared absorption and reflection spectra, refraction index, and absorption coefficients, influencing glass composition, are also studied.

Chalcogenide glasses and fibers for applications in medicine

Chalcogenide glasses based on suplhides and selenides are very promising materials for various photonic applications, particularly for applications in medicine. Most of current optical fibers have been developed form ultrapure silica. While silica glasses are suitable for optical components in telecommunications they exhibit high losses beyond 2 micrometers - a wavelength range important for clinical practice. Thus special glass materials 9from which fibers could be drawn) should be developed for optical power transmission beyond 2 micrometers . The investigation and preparation of vitreous materials that include sulphide, selenide and selenide- tellurite glass systems together with fluoride and heavy metal oxide glasses on the base of ZrF4, HfF4 and GeO2, TeO2, PbO, respectively are being pursued in our laboratory. This research is aimed at the development of both passive and active (rare-earth doped) optical fibers. In this contribution we concentrate on the doping of chalcogenide glasses by rare earth elements (Er, Pr, Nd). Although the major role of these glasses is assumed in the development of laser power delivery systems for applications in surgery, dentistry, dermatology and ophthalmology, they can equally be used for the diagnostics of human tissues. An example of colon tissue autofluorescence will be given.

Optimizing of multicomponent seleno-telluride glasses for optical fibers applied to power transmission at 10.6 μm

Optical, mechanical, thermophysical, electrical and dielectric properties of Ge-Se-Te and Ge-Sb-Se-Te glasses for the short-distance power transmitting fibers for use with CO and/or CO2 lasers are presented. The optimum glass composition Ge30Se35Te35 has been found.

Gex(Se1 − yTey)1 − x glasses for optical application

A technique for preparation of Ge x /Se 1 − x Te y / 1 − x glasses was developed. These glasses have no extrinsic and intrinsic absorptionbetween 8–12/um, oxygen concentration is 3–5 ppm and the value of absorption coefficient is estimated Lower than 10 −3 cm −1 at 10.6/um. Optimum composition seems to be Ge 25–30 Se 30–40 Te 30–40 . These glasses can be used for fiber drawing.

Sulfide and heavy metal oxide glasses for active fibers

Glass samples have been synthesized from sulfide and tellurite glasses. General chemical compositions are Ge0.25Ga0.10S0.65, Ge0.25Ga0.05As0.05S0.65, (TeO2)-(PbCl2)1-x with x equals 0.4 to 0.6 and (TeO2x-(ZnO)1-x with x equals 0.75 to 0.80. Samples doped with 500 to 12000 ppm rare earth in weight were also prepared. Sulfide glasses were made from pure components using a reactive atmosphere, which lead to glasses with a low OH content. Rare earth doped glasses are homogeneous when RE concentration is less than 3000 ppm. Heterogeneous inclusions arise beyond 1000 ppm RE when doping is made with chloride or oxide. Absorption and fluorescence measurements have been made. A YAG:Nd laser was used for excitation. The evolution of the fluorescence lifetime shown that the emission from the Pr3+ 1G4 level at 1.3 micrometers shows some concentration quenching above 1000 ppm Pr3+. The color and the optical quality of the tellurite glasses depend on crucible materials. Colorless samples are obtained with gold crucible while various colorations or defects are observed with Pt, SiO2 and Al2O3. Rare earth doping result in visible defects or inhomogeneities when concentration is larger than 1000 ppm. The chemical composition and the optical absorption of doped and undoped samples was examined. Fluorescence intensity of Pr and Dy is smaller in these HMO glasses than in the sulfide glasses, this results from higher phonon energy and higher OH concentration. Further development is required for future applications.

Autofluorescence spectroscopy of colorectal carcinoma: ex vivo study

Diagnosis established by means of fluorescence spectroscopy is currently used in the field of urology and bronchology. Its major advantage is that it allows the diagnosis of epithelial dysplasia or malignant proliferation even if routine diagnostic endoscopy fails to reveal any macroscopic changes. The authors present results of their observations that deal with fluorescence diagnosis of colorectal carcinoma. They examined the wet microscopic mounts of healthy colon mucosa and compared them to that prepared from colon mucosa affected by adenocarcinoma. The diagnosis of adenocarcinoma was verified by using clinical and histology means. Fluorescence spectra of tissue samples, excited by means of 488 and 514.5 nm lines of Ar ion laser and/or by He-Ne laser line 632.8 nm, have been studied. This study demonstrated differences in both the spectral shape and in the signal intensity (at unchanged spectral shape) of photoluminescence spectra emitted from tissue affected by adenocarcinoma as compared to that of healthy colon mucosa. The results encourage us to continue the study aimed at development of the diagnostic system usable in the clinical practice.

Optical characterization of glass materials doped with rare-earth elements

Sulphide glasses of GeGaS and GeGaAsS systems doped with rare earth ions are promising materials for various photonic applications. Because the solubility of rare earth elements ins influenced by the purity of host glass, namely by OH group concentration, the attention has been paid to the preparation of highly pure and homogeneous undoped and rare earth doped glasses. Particularly the systems Ge0.25Ga0.1-xS0.65Prx and Ge0.25Ga0.05- xAs0.05S0.65Prx with x equals 500, 1000, 3000, 6000 wt. ppm have been prepared. Synthesized materials system have been characterized by Raman and low-temperature photoluminescence spectroscopies. The optical Pr concentration has been found to be around 1000 wt.ppm. The appearance of temperature induced radiative transitions have been observed on GeGaS:Er samples.

Characterization of chalcogenide glasses for optoelectronics

Chalcogenide glasses - Ge25Ga10S65 , Ge25Ga5As5S65 , As2S3 , As2S2Se , As25e3 — have been synthesized and doped with ions of rare earth RE3 , in the concentration range of 500 to 6000 wt.ppm. Special processing makes possible to reduce the hydroxyle content and to incorporate rare earth ions without phase separation. Various physical measurements, including photoluminescence have been implemented. Main observations and results may be summurized as follows: -OHgroup concentration could be lowered below 5x105 mol.% in pure chalcogenide glasses - Rare earth ions are introduced into sulfide glasses at concentrations ranging from 500 to 6000.ppm. Homogeneous and clear samples are obtained up to 3000wt.ppm Pr3+. - Clusters and defects are observed when RE and OH concentrations increases,. -Abackground photoluminescence in based glasses and it depends on temperature.

Special glasses for passive and active IR fibers for medical and biomedical applications

General chemical compositions of prepared glasses with low OH group concentrations are Ge0.25Ga0.10S0.65, Ge0.25Ga0.05As0.05S0.65, (TeO2)x - (PbCl2)1-x with x equals 0.4 to 0.6 and (TeO2)x - (ZnO)1-x with x equals 0.75 to 0.80. Samples doped with 500 to 12000 ppm rare earth in weight were prepared. Rare earth doped glasses are homogeneous when RE concentration is less than 3000 ppm. Heterogeneous inclusions arise beyond 1000 ppm RE when doping is made with chloride or oxide. Electron microscopy, absorption and fluorescence measurements have been made. YAG:Nd. Ar, He-Ne lasers were used for excitation of photoluminescence. The color and optic quality of the tellurite glasses depend on crucible materials. Rare earth doping results in visible defects or inhomogeneities when concentration is larger than 1000 ppm. The chemical composition and the optical absorption of doped and undoped samples was examined. Fluorescence intensity of Pr and Dy is smaller in these HMO glasses than in the sulfide glasses, which results from higher phonon energy and higher OH concentration. Further development is required for future applications.