L. Nagli

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...

Silver halide single-mode fibers for the middle infrared

There is an interest in single-mode fibers that are highly transparent in the middle infrared. Such fibers would be valuable for spectroscopy, interferometry, fiber lasers, and heterodyne detection. We developed core-clad fibers made of crystalline silver halides, with external diameter 900 μm, small core diameters (50–60 μm) and an extremely small difference (∼0.004) between the indices of refraction of the core and the clad. These fibers behaved as single-mode fibers at the wavelength 10.6 μm.

Scanning near-field infrared microscopy based on tapered silver–halide probes

We report on developments in scanning near-field infrared microscopy where the scanning elements are silver–halide tapered fiber probes. These probes showed good transmission efficiency and a transparency over a very wide spectral range (0.6–10 μm), which may prove useful in high-resolution spectroscopy. We performed spatial characterization of the radiation distribution emitted from these probes, using the knife-edge technique. The obtained profiles, measured both for midinfrared and for visible radiation, were consistent with theoretical predictions. Images of subwavelength features, acquired with these probes, validated their potential for super-resolution microscopy, spectroscopy, and radiometry in the midinfrared.

Ordered bundles of infrared-transmitting AgClBr fibers: optical characterization of individual fibers.

Silver halide (AgCl(x) Br(1-x)) crystals were extruded to form polycrystalline fibers that are highly transparent in the spectral range 3-30 mum. Ordered bundles consisting of as many as 9000 fibers were fabricated by multiple extrusion steps. The transmission loss of an individual fiber in the 100-fiber bundles was 0.12 dB/cm, and the cross talk between neighboring fibers in the 900-fiber bundles was 25%. Thermal images of bodies at room temperature have been transmitted through the bundles. Such ordered bundles provide a solution for the problem of thermal imaging in regions where there is no line of sight between a thermal camera and a warm object.

The nature of unusual luminescence in natural calcite, CaCO3

Abstract The unusual luminescence of particular varieties of natural pink calcite (CaCO3) samples was studied by laser-induced time-resolved luminescence spectroscopy at different temperatures. The luminescence is characterized by intense blue emission under shortwave UV lamp excitation with an extremely long decay time, accompanied by pink-orange luminescence under longwave UV excitation. Our investigation included optical absorption, natural thermostimulated luminescence (NTL) and Laser-Induced Breakdown Spectroscopy (LIBS) studies. Two luminescence centers were detected: (1) a narrow violet band, with λmax = 412 nm, Δ = 45 nm, two decay components of τ1 = 5 ns and τ2 = 7.2 ms, accompanied by very long afterglow, and an orange emission band with λmax = 595 nm, Δ = 90 nm, and τ = 5 ns. Both luminescence centers are thermally unstable with the blue emission disappearing after heating at 500 °C, and the orange emission disappearing after heating at different temperatures starting from 230 °C, although sometimes it is stable up to 500 °C in different samples. Both centers have spectral-kinetic properties very unusual for mineral luminescence, which in combination with extremely low impurity concentrations prevent their identification with specific impurity related emission. The most likely explanation of these observations may be the presence of radiation-induced luminescence centers. The long violet afterglow is evidently connected with trapped charge carrier liberation, with their subsequent migration through the valence band and ultimate recombination with a radiation-induced center responsible for the unusual violet luminescence.

Raman scattering spectroscopy for explosives identification

Real time detection and identification of explosives at a standoff distance is a major issue in efforts to develop defense against so-called Improvised Explosive Devices (IED). It is recognized that the only technique, which is potentially capable to standoff detection of minimal amounts of explosives is laser-based spectroscopy. LDS technique belongs to trace detection, namely to its micro-particles variety. We applied gated Raman and time-resolved luminescence spectroscopy for detection of main explosive materials, both factory and homemade. Raman system was developed and tested by LDS for field remote detection and identification of minimal amounts of explosives on relevant surfaces at a distance of up to 30 meters.

Silver-halide fiber tip as a beam homogenizer for infrared hollow waveguides

A beam-homogenizing device consisting of a short tip of silver-halide infrared fiber eliminates the low-order multimode effect generated by bending of hollow guides. A series of experiments with a CO(2) laser shows that the solid fiber functions as a homogenizer with a small insertion loss of 0.2dB.

Laser-induced time-resolved luminescence of natural titanite CaTiOSiO4

Abstract The time-resolved laser-induced luminescence spectroscopy of natural titanite enables to detect and identify emission lines of trivalent rare-earth elements, such as Sm, Eu, Er, Pr, Tm, Nd, and transition elements, such as Cr 3+ in strong and intermediate crystal field sites. Energy migration between Cr 3+ site and Nd 3+ is detected.

Gated Raman spectroscopy: potential for fundamental and applied mineralogy

Using calcite as example, we demonstrate how a pulsed UV laser and time-resolved detection methods allow discrimination of Raman signals from strong luminescence background light. It is done in time domain and spectral domain. In time domain experiments, we use the fact that Raman scattering is produced almost instantaneously, whereas for emissions associated with luminescence, a minimum of hundreds of picoseconds elapse between electronic excitation and radiative decay. In the spectral domain, Raman peaks are very close to the UV excitation frequency whereas the luminescence is spectrally separated because of its larger Stokes shift compared to Raman. The UV gated Raman technique is a potential tool for remote sensing and online sorting of minerals.