Energy transfer assisted frequency upconversion in Ho 3+ doped fluoroindate glass

Experimental results are reported which show a strong evidence of energy transfer between Ho 3+ ions in a fluoroindate glass excited by a pulsed laser operating at 640 nm. We identified the origin of the blue and green upconverted fluorescence observed as being due to a Ho 3+-Ho 3+ pair interaction process. The dynamics of the fluorescence revealed the pathways involved in the energy transfer assisted upconversion process. © 2002 American Institute of Physics.

Blue upconversion enhancement by a factor of 200 in Tm 3+-doped tellurite glass by codoping with Nd 3+ ions

We investigated near-infrared-to-blue upconversion from thulium (Tm 3+) doped in tellurite glasses upon continuous wave excitation near 800 nm. We observed an enhancement of over two orders of magnitude of the upconverted emission at ∼480nm when neodymium (Nd 3+) ions were codoped with Tm 3+ ions. For comparison, using a Tm 3+:Nd 3+ codoped fluorozirconate glass as a reference material we observed a 40-fold enhancement of the blue emission. Analysis of the blue emission for samples with different doping levels of Nd 3+ ions showed that energy transfer between Nd 3+ and Tm 3+ is the mechanism responsible for the enhancement in upconversion. © 2002 American Institute of Physics. © 2002 American Institute of Physics.

Enhanced frequency upconversion in Er3+ doped fluoroindate glass due to energy transfer from Tm3+

Energy transfer processes between Er3+ and Tm3+ were investigated examining the frequency upconversion emissions in a fluoroindate glass pumped at 790 nm. A 60-fold enhancement in the emission at ≈670 nm originating from Er3+ was observed when Tm3+ at concentration of 2% was introduced in a sample containing 2% of Er3+. The results are explained considering the influence of cross-relaxation processes between the active ions. © 2002 Elsevier Science B.V. All rights reserved.

Frequency upconversion in rare-earth doped fluoroindate glasses

We present recent results on frequency upconversion (UPC) obtained in fluoroindate glasses (FIG) doped with Ho3+, Tm3+ and Nd3+ ions and codoped with Pr3+/Nd3+ and Yb3+/Tb3+ ions. The results for the Ho3+-doped samples show strong evidence of energy transfer (ET) between Ho3+ ions resonantly excited at 640 nm. The origin of the blue-green upconverted fluorescence observed was identified and the dynamics of the signals revealed the pathways involved in the UPC process. In the case of Tm3+-doped FIG, the samples were resonantly excited at 650 nm and the main mechanism that contributes for the red-to-blue upconversion is excited-state absorption (ESA). The FIG samples codoped with Pr3+/Nd3+ were excited at 588 nm in resonance with transitions starting from the ground state of the Nd 3+ and the Pr3+ ions. It was observed that the presence of Nd3+ ions enhanced the Pr3+ emission at 480 nm by two orders of magnitude. Multiphonon (MP)-assisted upconversion is also discussed for Nd3+-doped FIG pumped at 866 nm. Emission at 750 nm with a peculiar linear dependence with the laser intensity was observed and explained. A rate-equation model that includes MP absorption via thermally coupled electronic excited states of Nd3+ was developed and describes well the experimental results. The role played by effective phonon modes is clearly demonstrated. MP-assisted UPC process was also studied in Yb3+/ Tb3+-codoped FIG samples excited at 1064 nm, which is off-resonance with electronic transitions starting from the ground state. It was determined that the mechanism leading to Tb3+ emission in the blue is due to ET from a pair of excited Yb3+ ions followed by ESA in the Tb 3+ ions. © 2002 Académie des sciences/Éditions scientifiques et médicales Elsevier SAS.

Microstructure of doped barium titanate prepared from polymeric precursors

Barium titanate is used extensively as a dielectric in ceramic capacitors, particularly due to its high dielectric constant and low dielectric loss characteristics. It can be made semiconducting by addition of certain dopants and by proper modification of grains and grain boundary properties obtaining very interesting characteristics for various applications. The synthesis method and sintering regime have a strong influence on properties of obtained barium titanate ceramics. Doped barium titanate was prepared with Nb+5 and Y+3 ions as donor dopants, and with Mn+2 ions as acceptor dopant by polymeric precursors method. By this procedure nanosized powders were obtained after calcination. Sintering was performed in the temperature range of 1290°C to 1380°C The microstructure of doped BaTiO3 was performed using scanning electron microscopy. The influence of dopants and sintering temperature on grain size was analysed.

Short-chain di-ureasil ormolytes doped with potassium triflate: Phase diagram and conductivity behavior

Di-urea cross-linked poly(oxyethylene)/siloxane hybrids, synthesized by the sol-gel process and containing a wide concentration range of potassium triflate, KCF3SO3, have been analyzed by x-ray diffraction and differential scanning calorimetry. The pseudo-phase diagram proposed has been taken into account in the interpretation of the complex impedance measurements. The xerogels prepared are obtained as transparent, thin monoliths. At room temperature the highest conductivity found was 2 × 10-6 Ω-1 cm-1.

Rare earth doped HfO2 nanoparticles embedded in SiO2-HfO2 planar waveguides. Preparation, optical, structural and spectroscopic characterization

In this work we present results on the preparation of planar waveguides based on HfO2 and HfO2-SiO2. Stable sols containing europium and erbium doped HfO2 nanoparticles have been prepared and characterized. The nanosized sol was either deposited (spin-coating) on quartz substrates or embedded in (3-glycidoxipropil)trimethoxisilane (GPTS) used as a hybrid host for posterior deposition. The refractive index dispersion and luminescence characteristics were determined for the resulting HfO2 films. The optical parameters of the waveguides such as refractive index, thickness and propagation losses were measured for the hybrid composite. The planar waveguides present thickness of a few micra and support well confined propagating modes.

Collagen fibers in human prostatic lesions: histochemistry and anisotropies

The present study focuses on establishing patterns of collagen fibers distribution in prostatic nodular hyperplasia and adenocarcinomas, in comparison with the normal tissue. Sections of prostatic transurethral resection were subjected to Gömöri's method for collagen fibers and reticulin and analyzed under ordinary and polarized light microscopy. Controls and hyperplastic regions present collagen fibers with variable thickness that run in different directions, establishing a tridimensional network. These fibers exhibit birefringence and dichroism thus demonstrating their fibrillar integrity. On the other hand, increased variability in collagen fiber distribution and anisotropical properties occur in adenocarcinomas evaluated in accordance with the Gleason's score. In some of their areas, a well-defined collagen network delimitates the base of transformed epithelial cells whereas in other areas the collagen fibers are disorganized and do not establish a boundary between the epithelial structures and the stroma. In these areas, collagen is found in the stroma. It was also observed that adenocarcinoma tumor cells rest on a scaffold of thin and dendritic collagen fibers. Collagen fibers of the prostatic stroma of the adenocarcinomas may show a modification in arrangement and fibrillar compactness. In prostatic nodular hyperplasia, there is no change in collagen molecular integrity, since collagen affinity for silver and collagen birefringence are similar to controls. In adenocarcinoma with high dedifferentiation degree, thin and branched strongly argyrophilic and birefringent collagen fibers are detected in regions of cell proliferation. In the adjacent stroma, hyaline plaques are indicative of matrix degradation or remodellation.

Structural phase evolution of strontium-doped lead titanate thin films prepared by the soft chemical technique

Strontium-modified lead titanate thin films with composition Pb1-xSrxTiO3 were grown on Pt/Ti/SiO2/Si substrates using the polymeric precursor method. The structural phase evolution as a function of the Sr contents was studied using micro-Raman scattering, specular reflectance infrared Fourier transform spectroscopy, and x-ray diffraction. The results showed a gradual change from tetragonal to cubic structure, the transition occurring at about x = 0.58. The infrared reflectance spectra showed that the frequency of several peaks decreases as the strontium concentration increases. These features are correlated with a decrease in the tetragonal distortion of the TiO6 octahedra as the strontium concentration increases.

Spectroscopic studies of SnO2 doped with Cr, Co or Nb

SnO2 ceramics doped with different amounts of Co, Cr or Nb were investigated using visible and infrared spectroscopy at room temperature. Based on the observed d-d transitions the valence states of incorporated dopants were determined. Values of the optical band-gap were calculated in all samples. The infrared spectra of the samples displayed variations in the position, relative intensity and width of the bands, which were attributed to the presence of dopants.

X-ray-induced conductivity in iron-doped lithium niobate crystals

Illumination of photorefractive, iron-doped lithium niobate crystals (LiNbO 3:Fe) with x-rays generates a conductivity that we determine from the speed of hologram erasure. The doping levels of the crystals and the acceleration voltage of our x-ray tube are varied. A theoretical model is presented, which describes the obtained results. A decrease of the conductivity with increasing Fe 2+ concentration can be explained by assuming that holes are the dominant charge carriers for this short-wavelength illumination.

Sol-Gel Erbium-Doped Silica-Hafnia Planar and Channel Waveguides

Erbium activated SiO2 -HfO2 planar waveguides, doped with Er3+ concentrations ranging from 0.01 to 4 mol%, were prepared by sol-gel method. The films were deposited on v-SiO2 and silica-on-silicon substrates using dip-coating technique. The waveguides show high densification degree, effective intermingling of the two film components, and uniform surface morphology. The waveguide deposited on silica-on-silicon substrates shows one single propagation mode at 1.5μm, with a confinement coefficient of 0.81 and an attenuation coefficient of 0.8 dB/cm at 632.8nm. Emission in the C-telecommunication band was observed at room temperature for all the samples upon continuouswave excitation at 980 nm or 514.5 nm. The shape of the emission band corresponding to the 4I13/2 → 4I15/2 transition is found to be almost independent both on erbium content and excitation wavelength, with a FWHM between 44 and 48 nm. The 4I13/2 level decay curves presented a single-exponential profile, with a lifetime ranging between 1.1 - 6.6 ms, depending on the erbium concentration. Infrared to visible upconversion luminescence upon continuous-wave excitation at 980 nm was observed for all the samples. Channel waveguide in rib configuration was obtained by etching the active film in order to have a well confined mode at 1.5 μm.

Spectroscopic properties of Tm3+ doped fluoroindate glass

Optical absorption and fluorescence were investigated in Tm3+ doped fluoroindate glass. The spectroscopic parameters for transitions in the 4f11 configuration were determined. The fluorescence study revealed the origin of the frequency upconversion process as well as allowed to quantify the interaction between Tm3+ ions.

Infrared-to-visible frequency upconversion in transparent glass ceramics containing trivalent-rare-earth-doped nanocrystals

In this work we report on visible upconversion emission in Er 3+-, and Ho3+-doped PbGeO3-PbF 2-CdF2-based transparent glass ceramics under 980 nm infrared excitation. In erbium-doped vitroceramic samples, blue(410 ran), green(530, and 550 nm) and red(660 nm) emission signals were generated, which were identified as due to the 2H9/2, 2H 11/2, 4S3/2, and 4F9/2 transitions to the 4I15/2 ground-state, respectively. Intense red(650 nm) upconversion emission corresponding to the 5F5 - 5I8 transition and very small blue(490 nm) and green(540 nm) signals assigned to the 5F 2,3 - 5I8 and 4S2, 5F4 - 5I8 transitions, respectively, were observed in the holmium-doped samples. The 540 nm is the dominant upconversion signal in Ho3+-doped vitroceramics under 850 nm excitation. The dependence of the upconversion processes upon pump power and doping concentration are also investigated, and the main routes for the upconversion excitation processes are also identified. The comparison of the upconversion process in transparent glass ceramics and the precursor glass was also examined and the results revealed that the former present higher upconversion efficiencies.

Red, green, and blue upconversion luminescence in ytterbium-sensitized praseodymium-doped lead-cadmium-germanate glass

Blue, green, red, and near-infrared upconversion luminescence in the wavelength region of 480 - 740 nm in Pr3+/Yb3+-codoped lead-cadmium-germanate glass under 980 nm diode laser excitation, is presented. Upconversion emission peaks around 485, 530, 610, 645, and 725 nm which were ascribed to the 3P0 - 3HJ (J=4, 5, and 6), and 3P0 - 3FJ (J=2, and 3,4), transitions, respectively, were observed. The population of the praseodymium upper 3P0 emitting level was accomplished through a combination of ground-state absorption of Yb3+ ions at the 2F7/2, energy-transfer Yb3+(2F 5/2) Pr3+(3H4), and excited-state absorption of Pr3+ ions provoking the 1G4 - 3P0 transition. The dependence of the upconversion luminescence upon the Yb3+-concentration and diode laser power, is also examined, in order to subsidize the proposed upconversion excitation mechanism.