Cid B. de Araújo

Er3+-doped BaTiO3 nanocrystals for thermometry: Influence of nanoenvironment on the sensitivity of a fluorescence based temperature sensor

Frequency upconverted emissions centered at 526 and 547 nm from two thermodynamically coupled excited states of Er3+ doped in BaTiO3 nanocrystals were recorded in the temperature range from 322 to 466 K using a diode laser emitting at 980 nm as the excitation source. The ensemble measurements of the fluorescence intensity ratio (FIR) of the signals at 526 and 547 nm as a function of the temperature showed that the sensitivity (the rate in which the FIR changes with the temperature) of such sensor depends on the size of the nanocrystal. This is explained taking into consideration modifications of nonraditive relaxation mechanisms with the size of the nanocrystals.Frequency upconverted emissions centered at 526 and 547 nm from two thermodynamically coupled excited states of Er3+ doped in BaTiO3 nanocrystals were recorded in the temperature range from 322 to 466 K using a diode laser emitting at 980 nm as the excitation source. The ensemble measurements of the fluorescence intensity ratio (FIR) of the signals at 526 and 547 nm as a function of the temperature showed that the sensitivity (the rate in which the FIR changes with the temperature) of such sensor depends on the size of the nanocrystal. This is explained taking into consideration modifications of nonraditive relaxation mechanisms with the size of the nanocrystals.

Random fiber laser

We investigate the effects of two-dimensional confinement on the lasing properties of a classical random laser system operating in the incoherent feedback (diffusive) regime. A suspension of 250 nm rutile (TiO2) particles in a rhodamine 6G solution was inserted into the hollow core of a photonic crystal fiber generating the first random fiber laser and a novel quasi-one-dimensional random laser geometry. A comparison with similar systems in bulk format shows that the random fiber laser presents an efficiency that is at least 2 orders of magnitude higher.

Frequency upconversion in Er3+ doped PbO–GeO2 glasses containing metallic nanoparticles

The authors report the infrared-to-visible frequency upconversion (UPC) process in Er3+ doped PbO–GeO2 glasses containing silver nanoparticles (NPs) with an average diameter of 2.2nm. The absorption spectra of the samples present a band centered at 470nm due to the surface plasmons associated with the NPs. The intensity of the band grows with increasing NP concentration. The experiments were performed by exciting the samples with a 980nm diode laser and observing the UPC emissions in the red-green region. The enhanced UPC intensity is attributed to the local field effect in the proximity of the NPs.

Enhancement of Pr3+ luminescence in PbO–GeO2 glasses containing silver nanoparticles

Pr3+-doped PbO–GeO2 (PGO) glasses containing silver nanoparticles (NPs) were prepared and their spectroscopic characteristics were studied. The PGO samples and the nucleation of silver NP were obtained melting the starting oxide powders, quenching and annealing. Transmission electron microscopy was used to characterize the NP size distribution. Isolated silver particles with average diameter of 2 nm and aggregates with dimensions smaller than 100 nm were observed. Optical absorption and luminescence experiments were performed to investigate the properties of the composite system. Enhancement of the Pr3+ ions’ luminescence was observed due to the presence of the silver NP.

Measurements of nondegenerate optical nonlinearity using a two‐color single beam method

A two‐color ‘‘z’’ scan method is introduced to characterize the nonlinear refraction of optical materials in their absorptive region. We demonstrate the method by measuring the sign and the magnitude of the frequency nondegenerate nonlinearity in the absorptive region of semiconductor doped glasses.

Influence of silver nanoparticles in the luminescence efficiency of Pr3+-doped tellurite glasses

We studied the influence of silver nanoparticles (NPs) in the luminescence properties of TeO2–PbO–GeO2 glass doped with trivalent praseodymium (Pr3+) ions. The experiments were performed with samples containing different concentrations of NPs controlled by heat treatment of the glass. The enhancement of the Stokes luminescence with the increase of the NPs concentration was observed for samples excited at 454nm. The influence of the NPs on the frequency upconversion (anti-Stokes) emissions of Pr3+ under excitation at 520nm was also investigated. In this case, enhancement of the emissions around 460 and 486nm was observed and the excitation pathway is also discussed.

Reflection Z‐scan technique for measurements of optical properties of surfaces

Spatial modification of a Gaussian beam by reflection on a surface of a high‐absorbing material is investigated experimentally. A theoretical description in a geometrical‐optics approach is given. The usefulness and sensitivity of the method for applications in measuring laser induced surface deformation and Kerr‐like nonlinear coefficients is discussed.

Infrared‐to‐visible CW frequency upconversion in Er3+‐doped fluoroindate glasses

We report on efficient frequency upconversion in Er3+‐doped fluoroindate glasses. The process is observed under 1.48 μm laser diode excitation and results in the generation of strong blue (∼407 nm), green (∼550 nm), and red (∼670 nm) radiation. The main mechanism that allows for upconversion appears to be the energy transfer among Er3+ ions in excited states. The results illustrate the large potential of this new class of glasses for photonic applications.

Influence of metallic nanoparticles on electric-dipole and magnetic-dipole transitions of Eu3+ doped germanate glasses

Luminescence properties of Eu3+ doped germanate glasses containing either silver or gold nanoparticles (NPs) were investigated for excitation at 405 nm. Enhanced emissions and luminescence quenching of the Eu3+ transitions in the range from 570 to 720 nm were observed for samples having various concentrations of metallic NPs. Electric-dipole and magnetic-dipole transitions that originate from the Eu3+ level D50 exhibit large enhancement due to the presence of the metallic NPs. The results suggest that the magnetic response of rare-earth doped metal-dielectric composites at optical frequencies can be as strong as their electric response due to the confinement of the optical magnetic field.

Optical spectroscopy and frequency upconversion properties of Tm3+ doped tungstate fluorophosphate glasses

Tungstate fluorophosphate glasses of good optical quality were synthesized by fusion of the components and casting under air atmosphere. The absorption spectra from near-infrared to visible were obtained and the Judd–Ofelt parameters determined from the absorption bands. Transition probabilities, excited state lifetimes and transition branching ratios were determined from the measurements. Pumping with a 354.7 nm beam from a pulsed laser resulted in emission at 450 nm due to transition 1D2→3F4 in Tm3+ ions and a broadband emission centered at ≈550 nm attributed to the glass matrix. When pumping at 650 nm, two emission bands at 450 nm (1D2→3F4) and at 790 nm (3H4→3H6) were observed. Excitation spectra were also obtained in order to understand the origin of both emissions. Theoretical and experimental lifetimes were determined and the results were explained in terms of multiphonon relaxation.