Visible and near-infrared luminescent Eu3+ or Er3+ doped laponite-derived xerogels and thick films: Structural and spectroscopic properties

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

1.5 mu m and visible up-conversion emissions in Er3+/Yb3+ co-doped tellurite glasses and optical fibers for photonic applications

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Visible emission from Er-doped SnO2 thin films deposited by sol-gel

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Visible PL phenomenon at room temperature in disordered structure of SrWO4 powder

The SrWO4 (SWO) powders were synthesized by the polymeric precursor method and annealed at different temperatures. The SWO structure was obtained by X-ray diffraction and the corresponding photoluminescence (PL) spectra was measured. The PL results reveal that the structural order-disorder degree in the SWO lattice influences in the PL emission intensity. Only the structurally order-disordered samples present broad and intense PL band in the visible range. To understand the origin of this phenomenon, we performed quantum-mechanical calculations with crystalline and order-disordered SWO periodic models. Their electronic structures were analyzed in terms of band structure. The appearance of localized levels in the band gap of the order-disordered structure was evidenced and is a favorable condition for the intense PL to occur.

Holographic imaging with multimode, large free spectral range lasers in photorefractive sillenite crystals

The holographic imaging of rigid objects with diode lasers emitting in many wavelengths in a sillenite Bi12TiO20 photorefractive crystal is both theoretically an experimentally investigated. It is shown that, due to the multi-wavelength emission and the typically large free spectral range of this light source, contour fringes appear on the holographic image corresponding to the surface relief, even in single-exposure recordings. The influence of the number of emitted modes on the fringe width is analysed, and the possible applications of the contour fringes in the field of optical metrology are pointed out.

Temperature investigation of infrared-to-visible frequency upconversion in erbium-doped tellurite glasses excited at 1540 nm

Temperature investigation of infrared-to-visible frequency upconversion in erbium-doped tellurite glasses excited by CW laser radiation at 1540 nm and under cryogenic temperatures is reported. Intense upconversion emission signals around 530, 550 and 660 nm corresponding to the H-2(11/2), S-4(3/2), and F-4(9/2) transitions to the I-4(15/2) ground state were generated and studied as a function of the laser intensity and temperature. The upconversion excitation mechanism of the Er3+ ions emitting energy levels was accomplished via stepwise multiphoton absorption. The green upconversion luminescence exhibited a fivefold intensity enhancement when the temperature of the sample was varied in the range between 5 and 300 K. A maximum green upconversion intensity was attained around 120 K and a steady decreasing behavior for higher temperatures up to 300 K was observed. A model based upon conventional rate equations was used to model the observed temperature evolution of the upconversion luminescence. (C) 2002 Elsevier B.V. B.V. All rights reserved.

Infrared-to-visible frequency upconversion in Pr3+/Yb3+- and Er3+/Yb3+-codoped tellurite glasses

Upconversion luminescence and thermal effects in Pr3+/Yb3+- and Er3+/Yb3+-codoped 60TeO(2)-10GeO(2)-10K(2)O-10Li(2)O-10Nb(2)O(5) tellurite glasses excited by CW infrared radiation at 1.064 mum is reported. Generation of intense green and red fluorescence emission in Er3+/Yb3+-codoped samples and appreciable upconversion luminescence in the wavelength region of 450-680 nm in Pr3+/Yb3+-codoped samples is observed. Temperature-induced enhancement of X12 in the upconversion efficiency in Er3+/Yb3+- and X10 in the Pr3+/Yb3+-doped samples is demonstrated. (C) 2002 Elsevier B.V. B.V. All rights reserved.

UV-visible absorption characteristics of TEOS-derived and Cr-doped silica sonogels aged in different pH solutions and heat treated up to 600 degrees C

Cr-doped xerogels were obtained by sol-gel process from the acid-catalyzed and ultrasound-stimulated hydrolysis of tetraethoxysilane (TEOS) with addition of CrCl3.6H(2)O in water solution during the liquid step of the process. The gels were aged immersed in different pH solutions for about 30 days, after that they were allowed to dry. The samples were annealed at temperatures ranging from 40 to 600degreesC and analyzed by UV-visible absorption spectroscopy. Cr3+ is the preferable oxidation state of the chromium ion in the gels annealed up to 250-300degreesC, in the case of aging in solutions of pH=5 and 11. A high UV absorption below similar to320 nm, due to the host gel, and different absorption bands, depending on the temperature, due to the chromium ion were observed in the xerogels at temperatures below similar to250degreesC, in the case of aging in solutions of pH=1 and 2. These absorption bands have not been assigned. Above 300degreesC up to 600degreesC, Cr5+, and possibly Cr6+, are the preferable oxidation states of the chromium ion independent of the pH of the aging solution, so the xerogels turn to a yellowish appearance in all cases.

Single-exposure, photorefractive holographic surface contouring with multiwavelength diode lasers

We studied the use of multiwavelength diode lasers for surface profilometry through holographic recording in sillenite Bi(12)TiO(20) crystals. When such lasers are used, the holographic image from single-exposure recordings appears covered with interference fringes providing information on the surface relief of the object. By taking advantage of the narrow interference fringes due to the multiwavelength emission of the laser, we obtained interferograms by holographic recording with two reference beams, which improves the surface analysis by visual inspection and enhances the profilometry sensitivity. (c) 2005 Optical Society of America.

1.5 mu m emission and infrared-to-visible frequency upconversion in Er+3/Yb+3-doped phosphoniobate glasses

Sodium phosphoniobate glasses with the composition (mol%) 75NaPO(3)-25Nb(2)O(5) and containing 2 mol% Yb3+ and x mol% Er3+ (0.01 <= x <= 2) were prepared using the conventional melting/casting process. Er3+ emission at 1.5 mu m and infrared-to-visible upconversion emission, upon excitation at 976 nm, are evaluated as a function of the Er3+ concentration. For the lowest Er3+ content, 1.5 mu m emission quantum efficiency was 90%. Increasing the Er3+ concentration up to 2 mol%, the emission quantum efficiency was observed to decrease to 37% due to concentration quenching. The green and red upconversion emission intensity ratio was studied as a function of Yb3+ co-doping and the Er3+-Er3+ energy transfer processes. (c) 2006 Elsevier B.V. All rights reserved.

Conditions giving rise to intense visible room temperature photoluminescence in SrWO4 thin films: the role of disorder

The nature of intense visible photoluminescence at room temperature of SrWO4 (SWO) non-crystalline thin films is discussed in the light of experimental results and theoretical calculations. The SWO thin films were synthesized by the polymeric precursors method. Their structural properties have been obtained by X-ray diffraction data and the corresponding photoluminescence (PL) spectra have been measured. The UV-vis optical spectra measurements suggest the creation of localized states in the disordered structure. The photoluminescence measurements reveal that the PL changes with the degree of disorder in the SWO thin film. To understand the origin of visible PL at room temperature in disordered SWO, we performed quantum-mechanical calculations on crystalline and disordered SWO periodic models. Their electronic structures are analyzed in terms of DOS, hand dispersion and charge densities. We used DFT method with the hybrid non-local B3LYP approximation. The polarization induced by the symmetry break and the existence of localized levels favors the creation of trapped holes and electrons, giving origin to the room temperature photoluminescence phenomenon in the SWO thin films. (c) 2004 Elsevier B.V. All rights reserved.

Infrared-to-visible CW frequency upconversion in erbium activated silica-hafnia waveguides prepared by sol-gel route

70SiO(2)-30HfO(2) mol% planar waveguides, doped with Er3+ with concentrations ranging from 0.3 to 2 mol% were prepared by sol-gel route, using dip-coating deposition on vitreous-SiO2 substrates. Infrared-to-visible upconversion emission, upon excitation at 980 nm, has been observed for all the samples. The upconversion results in green, red and blue emissions. The investigation of the upconversion dynamic as a function of the Er3+ concentration and excitation power, show that processes such as excited state absorption and energy transfer upconversion are effective. (C) 2003 Elsevier B.V. All rights reserved.

Totally visible transparent chloro-sulphide glasses based on Ga2S3-GeS2-CsCI

In this paper, the influence on optical properties of alkali halides such as CsCl in a covalent glassy matrix has been investigated. Chalcogenide glasses belonging to the (GeS2)-(Ga2S3)-CsCI system with high ratio of CsCl present an entire transparency in the visible range. These glasses maintain good transmission up to 12 mu m. Furthermore, the thermo-mechanical properties and the glass hygroscopicity have been investigated as function of the CsCl amount. This new generation of glasses presents a great interest for optical application. They could be used both for passive applications (multi-spectral imaging) and active applications for rare-earth doping due to their good transmission in the visible range, increasing optical pumping possibilities.

A comparative-study between visible-light-activated and autopolymerizing sealants in relation to retention

Two hundred twenty-nine first permanent molar occlusal surfaces were treated with sealants, from a group of sixty-one children. When the three sealants were analyzed at the end of the six-, twelve-, eighteen-, and twenty-four-month periods, it was observed that retentive loss was gradual. Both Concise and Delton showed superior retention when compared with Sealite.

Multiwavelength visible and white light generation by upconversion emission in Ho/Tm/Yb triply doped fluorogermanate glass-ceramic

Energy transfer excited multiwavelength visible upconversion emission and white light generation is described in a single sample of PbGeO(3)-PbF(2)-CdF(2) glass-ceramic triply doped With Ho/Tm/Yb under single infrared laser excitation. Blue (475 nm), green (540 mn), and red (650 nm), upconversion luminescence signals are generated, and the emissions are assigned, respectively, to thulium ((1)G(4)-(3)H(6)), and holmium ((5)S(2);(5)F(4)) -> (5)I(8), (5)F(5) -> (5)I(8)) ions transitions, both excited via successive energy transfers from ytterbium ions. It is experimentally shown that with a proper combination of the rare earth ions contents, white light may be produced, with the simultaneous generation of fluorescence with controllable intensities at the wavelengths of the three primary colours in a single sample and using a single near-infrared excitation source.