Diego S. da Silva

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.

Influence of silver nanoparticles on the infrared-to-visible frequency upconversion in Tm3+/Er3+/Yb3+ doped GeO2-PbO glass

We investigated the influence of silver nanoparticles (NPs) on the infrared-to-visible frequency upconversion (UC) in GeO2-PbO glass triply doped with thulium (Tm3+), erbium (Er3+), and ytterbium (Yb3+) ions. The NPs were nucleated inside the samples by heat-treatment of the germanate glass that included small amount of AgNO3 in the starting composition. When excited at 980 nm, in resonance with the Yb3+ transition 2F7/2 → 2F5/2, the samples emit blue light at ≈477 nm due to the Tm3+ ions, green light at ≈530 nm and ≈550 nm due to the Er3+ ions, and red light at ≈652 nm due to Tm3+ and at ≈660 nm due to the Er3+ ions. Due to the silver NPs, the photoluminescence intensity grows by ≈60% in comparison with a sample having the same composition but without silver NPs. This is the first time that UC enhancement due to metallic NPs is investigated for a triply rare-earth (RE) doped glass. The results indicate the possibility of development of more efficient three-dimensional RE based color displays by nucleatio...

Infrared-to-visible upconversion emission in Er3+ doped TeO2-WO3-Bi2O3 glasses with silver nanoparticles

The influence of silver nanoparticles (NPs) on the frequency upconversion luminescence in Er3+ doped TeO2-WO3-Bi2O3 glasses is reported. The effect of the NPs on the Er3+ luminescence was controlled by appropriate heat-treatment of the samples. Enhancement up to 700% was obtained for the upconverted emissions at 527, 550, and 660 nm, when a laser at 980 nm is used for excitation. Since the laser frequency is far from the NPs surface plasmon resonance frequency, the luminescence enhancement is attributed to the local field increase in the proximity of the NPs and not to energy transfer from the NPs to the emitters as is usually reported. This is the first time that the effect is investigated for tellurite-tungstate-bismutate glasses and the enhancement observed is the largest reported for a tellurium oxide based glass.

Enhanced Optical Properties of Germanate and Tellurite Glasses Containing Metal or Semiconductor Nanoparticles

Germanium- and tellurium-based glasses have been largely studied due to their recognized potential for photonics. In this paper, we review our recent studies that include the investigation of the Stokes and anti-Stokes photoluminescence (PL) in different glass systems containing metallic and semiconductor nanoparticles (NPs). In the case of the samples with metallic NPs, the enhanced PL was attributed to the increased local field on the rare-earth ions located in the proximity of the NPs and/or the energy transfer from the metallic NPs to the rare-earth ions. For the glasses containing silicon NPs, the PL enhancement was mainly due to the energy transfer from the NPs to the Er3+ ions. The nonlinear (NL) optical properties of PbO-GeO2 films containing gold NPs were also investigated. The experiments in the pico- and subpicosecond regimes revealed enhanced values of the NL refractive indices and large NL absorption coefficients in comparison with the films without gold NPs. The reported experiments demonstrate that germanate and tellurite glasses, having appropriate rare-earth ions doping and NPs concentration, are strong candidates for PL-based devices, all-optical switches, and optical limiting.

TiO2@Silica nanoparticles in a random laser: Strong relationship of silica shell thickness on scattering medium properties and random laser performance

A TiO2@Silica nanoparticle has been introduced in a random laser. TiO2 particles with an average diameter of 0.41 μm were coated with silica shells of different thicknesses. Strong dependency of silica shell thickness on the medium scattering strength was found. A mathematical relationship between the scattering mean free path, random laser threshold, and random laser efficiency was developed. Higher efficiency, lower laser threshold, narrower bandwidth, and longest photobleaching lifetime were obtained in the random laser that had increased silica shell thickness. Optical colloidal stability and light coupling enhancement with scattering particles, provided by silica shell, should lead to improved laser performance.

Nonlinear optical properties of Bi2O3-GeO2 glass at 800 and 532 nm

The nonlinear (NL) optical properties of glassy xBi2O3-(1−x) GeO2 with x = 0.72 and 0.82 were investigated. The experiments were performed with lasers at 800 nm (pulses of 150 fs) and 532 nm (pulses of 80 ps and 250 ns). Using the Kerr gate technique, we observed that the NL response of the samples at 800 nm is faster than 150 fs. NL refraction indices, |n2|≈ 5 × 10−16 cm2/W, and two-photon absorption coefficients, α2, smaller than 0.03 cm/GW, were measured at 800 nm. At 532 nm, we measured the NL transmittance of the samples. From the results obtained, we determined α2 ≈1 cm/GW and excited-state absorption cross-sections of ≈10−22 cm2 due to free-carriers.

Femtosecond laser-written double line waveguides in germanate and tellurite glasses

The authors report the fabrication and characterization of passive waveguides in GeO2–PbO and TeO2–ZnO glasses written with a femtosecond laser delivering pulses with 3μJ, 30μJ and 80fs at 4kHz repetition rate. Permanent refractive index change at the focus of the laser beam was obtained and waveguides were formed by two closely spaced laser written lines, where the light guiding occurs between them. The refractive index change at 632 nm is around 10-4 . The value of the propagation losses was around 2.0 dB/cm. The output mode profiles indicate multimodal guiding behavior. Raman measurements show structural modification of the glassy network. The results show that these materials are potential candidates for passive waveguides applications as low-loss optical components.

Influence of silicon nanocrystals on the performance of Yb3+/Er3+: Bi2O3-GeO2 pedestal waveguides for amplification at 1542 nm

This paper reports for, the first time, the influence of silicon nanocrystals on the photoluminescence and optical gain of Yb3+/Er3+ codoped Bi2O3−GeO2 waveguides for amplification at 1542 nm. Pedestal waveguides were fabricated by RF- sputtering followed by optical lithography and reactive ion etching. RF-sputtering followed by heat treatment produced silicon nanocrystals with average size of 8 nm and resulted in a photoluminescence enhancement of about 10 times for the 520 nm and 1530 nm emission bands. The resulting internal gain was 5.5 dB/cm at 1542 nm, which represents and enhancement of ∼50%, demonstrating potential for applications in integrated optics.

Luminescence of Er3+ doped TeO2-ZnO glass containing silicon nanocrystals

We investigate the influence of silicon nanocystals on Er3+ doped TeO2-ZnO. Large enhancement of the photoluminescence is observed. This is the first observation of photoluminescence enhancement in Er3+ doped TeO2-ZnO composites due to silicon nanocrystals.