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Blue-emitting bismuth-doped lanthanum oxide (La2O3: Bi3+) with various concentrations of Bi was synthesized using the sol–gel combustion method and used for visualization of latent fingerprints (LFPs). An X-ray diffraction (XRD) study revealed the hexagonal structure of the phosphors and total incorporation of the bismuth in the La2O3 matrix. Field Emission Scanning Electron Microscopy (FE-SEM) and Fourier Transform Infrared Spectroscopy (FTIR) were used to study the morphology and the relative vibrations of the synthesized samples. Photoluminescence (PL) studies showed strong blue emission around 460 nm due to the 3P1 → 1S0 transition. Clear bright-blue fingerprint images were obtained with the powder dusting method on various surfaces like aluminum, compact discs, glass, wood and marble. A first evaluation of these images indicated a clear visualization of all three levels of details and a very high contrast ranging from 0.41 on marble to 0.90 on aluminum. As a further step, we used an algorithm for extracting fingerprint minutiae with which we succeeded in detecting all three levels of fingerprint details and even the most difficult ones, like open and closed pores. According to these analyses, La2O3: Bi phosphor is demonstrated to be an effective blue fluorescent powder for excellent visualization of latent fingerprints. [ABSTRACT FROM AUTHOR]

In this work, we investigated the potential of Eu3+/Dy3+-codoped Y2Sn2O7 fluorescent nanophosphors to visualize latent fingermarks. We prepared these nanophosphors with various doping concentrations by the conventional coprecipitation reaction. The crystal structure, morphology, luminescence properties, and energy transfer mechanisms were studied. The crystalline phase was characterized by X-ray diffraction and crystal structure refinement using the Rietveld method. XRD measurements showed that the samples crystallized in the pure single pyrochlore phase with few more peaks originated from secondary phases and impurities generated during phosphor production, and that Eu3+ ions occupied D3d symmetry sites. The average crystallite size after mechanical grinding was less than 100 nm for all compositions. The optical characterization showed that, when excited under 532 nm, the Eu3+/Dy3+-codoped Y2Sn2O7 samples' main intense emission peaks were located at 580–707 nm, corresponding to the 5D0→7Fj (j = l, 2, 3, and 4) transitions of europium. In fact, the 5D0→7F2 hypersensitive transition is strongly dependent on the local environment and was quite weak in Eu3+:Y2Sn2O7 at low Eu3+ doping levels. We found that the presence of Dy3+ as a codopant permitted enhancing the emission from this transition. The calculated PL CIE coordinates for the synthesized nanophosphors were very close to those of the reddish-orange region and only slightly dependent on the doping level. Various surfaces, including difficult ones (wood and ceramic), were successfully tested for latent fingerprint development with the prepared Eu3+/Dy3+-codoped Y2Sn2O7 fluorescent nanophosphor powder. Thanks to the high contrast obtained, fingerprint ridge patterns at all three levels were highlighted: core (level 1) islands, bifurcation, and enclosure (level 2), and even sweat pores (level 3). [ABSTRACT FROM AUTHOR]

Results of a room-temperature polarized infrared (IR) spectroscopic investigation of two Nd:BaYF crystals are reported.

Yb doped Lu3Al5O12 single crystal fibers has been grown with various Yb3+ ion concentrations: 2%, 5%, 10%, 15%, and 50% Yb doping levels. The diameter of the fibers is around 3 mm and their length is up to 110 mm. The fibers have been annealed in air at 1400 °C for 24 h to remove Yb2+ produced during the growth in the fibers. Structural characterization by x-ray diffraction method has been performed to confirm the monocrystalline phase and the orientation of the fibers. Absorption measurements have been performed on different pieces of the fibers to check the homogeneity of the distribution of Yb3+ along the fiber length. The results indicate that the distribution coefficient is close to 1. The fluorescence lifetime was measured for different Yb3+ concentrations. Results are in agreement with the literature and can be interpreted as a mixture of the radiation trapping and concentration quenching effects. The emission cross section has been calculated both from absorption spectra and from emission data. The two different independent methods give similar results, but emission data suffer from strong reabsorption effects on some of the lines. On the zero phonon line at high doping levels a central dip appears that can be interpreted with a reabsorption model. [ABSTRACT FROM AUTHOR]

Single crystal lithium niobate fibers with diameters ranging from 1 to 3 mm have successfully been grown by the micro-pulling-down technique. The fibers are doped with various Er doping levels from 0 to 0.7 mol % and appear to be transparent and crack-free. The study includes x-ray structural investigation and complete spectroscopic characterization. The analysis shows a good homogeneity of composition, and the comparison with bulk crystals demonstrates the good optical quality of the samples. Particular attention has been devoted to the measurements of the fluorescence decay time of the 4I13/2 Er level, which has been carried out with a particular technique in order to avoid radiation trapping effects. Results are in agreement with the literature both in the case of bulk crystals and of fibers. Reliable polarized emission cross section in the 1.5 μm region are presented. [ABSTRACT FROM AUTHOR]

Spectroscopic properties of thulium-doped germanate, silica, and phosphate glasses were measured and compared since such glasses are of interest as materials for fiber lasers in the eye-safe wavelength region. 3F4 excited state fluorescence decay dynamics was investigated at temperatures from 8 to 300 K and the results revealed a strong dependence of the 3F4 lifetime on the host matrix. The temperature-dependent stimulated emission cross section was obtained by using the Fuchtbauer–Ladenburg technique. In phosphate glass the fluorescent lifetime is short, making this material difficult to use for 2 μm laser purposes. Tm3+-doped germanate glass shows a longer lifetime than silica, a comparable value of stimulated emission cross section and some interesting temperature-independent properties. [ABSTRACT FROM AUTHOR]

In this work we present the growth and spectroscopic investigation of Er3+ in CaWO4 single crystals. Er3+ polarized absorption has been measured at room temperature from UV to 1700 nm, and the fluorescence from the most important emitting states from the visible to the infrared has been recorded at 10 and 300 K in the two possible polarizations. The lifetimes of the lower lying excited states have been measured as a function of the temperature to evaluate the contribution of nonradiative decay processes. The absorption spectra enabled us to determine radiative lifetimes of the emitting states by means of the the Judd-Ofelt approach. The stimulated emission cross section has been estimated for the 1.5 μm transition. A comparison of the theoretical and experimental results permitted to obtain an estimate of the actual Er3+ doping level. A calculation of the effective gain cross section for the 1.5 μm transition is also presented. These experimental results are discussed in order to evaluate the potentialities of Er3+ in this material as active medium in solid state laser devices. [ABSTRACT FROM AUTHOR]

In this work we present the growth and spectroscopic investigation of Er3+ in CaWO4 single crystals. Er3+ polarized absorption has been measured at room temperature from UV to 1700 nm, and the fluorescence from the most important emitting states from the visible to the infrared has been recorded at 10 and 300 K in the two possible polarizations. The lifetimes of the lower lying excited states have been measured as a function of the temperature to evaluate the contribution of nonradiative decay processes. The absorption spectra enabled us to determine radiative lifetimes of the emitting states by means of the the Judd-Ofelt approach. The stimulated emission cross section has been estimated for the 1.5 μm transition. A comparison of the theoretical and experimental results permitted to obtain an estimate of the actual Er3+ doping level. A calculation of the effective gain cross section for the 1.5 μm transition is also presented. These experimental results are discussed in order to evaluate the potentialities of Er3+ in this material as active medium in solid state laser devices. [ABSTRACT FROM AUTHOR]

Anti-Stokes cooling has been observed in an Yb3+-doped BaY2F8 single crystal. Single crystals have been grown by the Czochralski technique. The absorption spectra and the emission properties have been measured at room temperature and at 10 K. The energy positions of the Stark sublevels of the ground and the excited state manifolds have been determined and separated from the vibronic substructure. The intrinsic decay time of the 2F5/2 level has been measured taking care of avoiding the effect of multiple reabsorption processes. The theoretical and experimental cooling efficiencies of Yb:BaY2F8 are evaluated and compared with respect to those of the most frequently investigated materials for laser cooling. A temperature drop of almost 4 K was measured by pumping the crystal with 3 W of laser radiation at ∼1025 nm in single pass configuration with a cooling efficiency of ∼3%. [ABSTRACT FROM AUTHOR]

X-ray diffraction method is used for structural characterization of the monocrystalline phase and the orientation of the Yb doped [Lu.sub.3][Al.sub.5][O.sub.12] single crystal fibers grown with various [Yb.sup.3+] ion concentrations. The results revealed that the micro-pulling down technique is capable of producing single cyrstalline materials with uniform distributions of active dopants and optical quality comparable to that of bulk crystals created by conventional melt growth techniques.