Qing Xiang

Green upconversion luminescence in Er3+:BaTiO3 films

Green upconversion emissions at 548 and 528 nm have been obtained from sol-gel derived nanocrystalline Er3+:BaTiO3 films under 980 nm excitation. The green emissions are attributed to the ground-state (4I15/2) -directed transitions from 2H11/2 (528 nm) and 4S3/2 (548 nm) of Er3+ ions. Analysis of the temporal evolution of the emission at 548 nm shows that both excited state absorption of individual ion and energy transfer between the two neighboring ions contribute to the upconversion emissions in Er3+ (3 mol %):BaTiO3 film. The lifetime of the dominant emission at 548 nm is about 90 μs.

Photoluminescence at 1.54 μm in sol-gel-derived, Er-doped BaTiO3 films

Abstract Nanostructured Er-doped BaTiO 3 films were deposited by the sol-gel method on SiO 2 /Si substrates. The spontaneous luminescence in the films at 1.54 μm was observed under the excitation of both 514 and 980 nm lasers. Transient photoluminescence showed that, for the Er:BaTiO 3 film containing 3.0 mol% Er, the decay of the 1.54 μm emission is a single exponential decay with a 1/ e lifetime of ∼5 ms. Concentration quenching was observed for the film containing 5.0 mol% Er, which was attributed to energy transfer and cross relaxation between closely sited Er 3+ ions in the BaTiO 3 lattice.

Up-conversion emission in violet from yellow in Nd3+: SiO2–TiO2–Al2O3 sol-gel glasses

This paper reports an up-conversion emission in violet (408 nm) from Nd3+-doped 93SiO2:7TiO2:20AlO1.5 glasses synthesized by the sol-gel process. Upon excitation at 583 nm (4I9/2→4G5/2), a bright violet up-conversion emission at 408 nm has been observed. The behavior of the up-conversion luminescence has been compared with that of the normal luminescence at both 408 and 1064 nm. The results show that while no concentration quenching for up to 2 mole Nd content is observed for the up-conversion emission, such an effect can be observed for the normal luminescence cases. Although the up-conversion luminescence has a shorter lifetime and weaker intensity, it is of use to the development of sol-gel glass-based waveguide lasers operating at the violet wavelength.

Preparation and optical properties of neodymium-doped sol-gel glasses using trimethylphosphate as P2O5 precursor

The Nd3+ ions doped bulk glasses and thin films with the trimethylphosphate (TMP) as the precursor of P2O5 were prepared by the sol-gel technique. Their optical properties have been investigated. The Fourier Transform IR (FTIR) of Nd3+ doped SiO2-TiO2-P2O5 films have been measured to study the influence of P2O5 content in the removal of hydroxyl group. Fluorescence spectral results show stronger fluorescence intensity along with the narrowing of the emission bands due to the availability of the co-dopant P2O5 in the sol-gel glasses compared with those of aluminum co-doped glasses. Our experimental results show that up to 6wt percent of Nd2O3 could be incorporated into the P2O5-SiO2 glass matrix without significant fluorescence quenching effect due to the usage of the TMP as a precursor. We have also found that the hydroxyl groups could easily be removed at lower temperatures, as we increase the P2O5 content. It indicates that the P2O5 co-doping has a great potentiality in reducing the process temperature.

Spectroscopic and photoluminescent studies of magnesium- and erbium-codoped lithium niobate crystal

A heavily magnesium (5.0 mol%) and erbium (2.0 mol%) codoped lithium niobate crystal has been grown using Czochralski method. The crystal is highly transparent and has strong resistance to photorefractive damage. Spectroscopic study showed that the crystal exhibits the typical f-f transitions of erbium ions. Photoluminescence at 1.54 micrometers was measured under excitations at 514 nm from an Ar+ laser and 980 nm from a GaAs laser diode. The temporal evolution of the 1.54 micrometers emission showed a single-exponential decay with a lifetime of approximately 5 ms. Upconversion property of the crystal under 980 nm excitation was also studied and the transient spectrum of the green emission at 548 nm also yields a single-exponential decay with a lifetime of approximately 35 microsecond(s) . The results have shown that clustering and pairing of Er ions could be effectively avoided by magnesium codoping.

Fabrication of ridge waveguides from sol-gel derived Nd-doped SiO/sub 2/-TiO/sub 2/-Al/sub 2/O/sub 3/ glass films

Rare earth doped glass waveguide amplifiers are being actively researched because of their potential applications in DWDM networks. We have fabricated ridge channels from sol-gel derived Nd-doped SiO/sub 2/-TiO/sub 2/-Al/sub 2/O/sub 3/ glass films using laser writing lithography and reactive ion etching (RIE). The SEM pictures show that the ridge is properly formed according to our design. The top surface of the ridge is smooth as a result of the Ti and Ni cap protection. However, the side-wall and the etched substrate are much rougher. We believe that the side-wall can be smoothed by re-annealing the channel and the propagation loss can be further reduced by burying the channel through depositing an upper cladding layer around the ridge.

Deposition and characterization of Er+3-doped, Al co-doped sol-gel silica films on SOS

Abstract Up to 18 layers of crack-free Er-doped sol-gel silica films co-doped with Al were deposited on SOS (silica on silicon) by multiple spin-coating and rapid thermal processing (RTP). The properties of the films were studied using ellipsometry, FTIR (Fourier Transform Infrared) Spectroscopy, AFM (atomic force microscopy) and XRD (X-ray diffraction). The results showed that, compared with air environment, a moderate (45–50 mbar) vacuum annealing environment could remove water molecules (H2O) in the prepared film more effectively and yield smoother film surface.

Processing and optical properties of Nd3+-doped SiO2-TiO2-Al2O3 planar waveguides

We report here the processing and optical characterization of Nd3+-doped SiO2-TiO2-Al2O3 planar waveguides deposited on SOS substrates by the sol-gel route combined with spin-coating and rapid thermal annealing. The recipes used for preparing the solutions by sol-gel route are in mole ratio of 93SiO2:20AlO1.5: x ErO1.5. In order to verify the residual OH content in the films, FTIR spectra were measured and the morphology of the material by the XRD analysis. Five 2-layer films annealed at a maximum temperature of 500 degrees C, 700 degrees C, 900 degrees, 1000 degrees C, 1100 degrees C respectively were fabricated on silicon. The FTIR and XRD curves show that annealing at 1050 degrees C for 15s effectively removes the OH in the materia and keeps the material amorphous. The propagation loss of the planar waveguides was measured by using the method based on scattering in measurements and the result was obtained to be 1.54dB/cm. The fluorescence spectra were measured with 514nm wavelength of Ar+ laser by directly shining the pump beam on the film instead of prism coupling. The results show that the 1 mole Nd3+ content recipe has the strongest emission efficiency among the four samples investigated.

Fluorescence lifetime study on sol-gel derived Er3+-doped SiO2-TiO2-Al2O3 planar waveguides

In the present paper, we report the preparation of Er3+ doped SiO (formula available in paper) planar waveguides deposited on SOS Silica on silicon substrates using sol-gel process combining with spin-coating and rapid thermal annealing. The recipes used for preparing the solutions by sol-gel process are (formula available in paper). The fluorescence spectra and lifetimes of the planar waveguides were measured under the excitation of 514 nm wavelength from an Ar+ laser. The lifetimes of 3.80 ms, 3.07 ms and 1.59 ms were obtained for 0.5 mole, 1.0 mole and 2.0 mole of Er3+ content planar waveguides respectively. The decay mechanism and the factors that influence the lifetime of the sol-gel planar waveguides have been analyzed.

Up-conversion luminescence of a violet color from sol-gel derived Nd3+:SiO2+Al2O3 glasses

Solid-state up-conversion lasers are found to be practical alternatives to frequency doubling techniques for the conversion of infrared radiation into visible light. Several applications, such as under-water optical communications and biomedical sensors, await the development of compact, efficient room-temperature devices that can operate at wavelengths not commonly obtainable by conventional laser sources. Such up-conversion lasers are considered as possible solutions to immediate technological problems. Trivalent rare-earth ions doped in different glasses and in certain crystals demonstrate up-conversion emissions in the visible wavelength range. The 4fn electronic level structures of these ions provide many long-lived intermediate levels, which could be populated using infrared radiation. These levels, together with some meta-stable higher lying levels, give rise to strong visible emissions [1]. Over the past few years, up-conversion emission (violet color) from Nd3+ ions has been reported in a variety of glasses based on certain chlorides, fluoroindate, fluorogallate, fluorozirconate, multi-component oxides and heavy metals [2–7]. In all these neodymium glasses, the up-conversion emissions are due to their low vibration frequencies and small phonon energy, and they are all synthesized by conventional melting methods. It is commonly believed that the Nd3+ in silica glasses cannot emit the up-conversion emission. In the literature, some researchers have stated that they did not observe violet up-conversion emission from the Nd3+doped silica glasses [6]. In addition, conventional silica fibers are not efficient in generating up-conversion signals from Nd3+ because of their large phonon frequencies. However, in our present work, we have indeed observed a relatively strong up-conversion emission in violet (399 nm) color upon excitation with a yellow light (580 nm) from Nd3+ : SiO2+Al2O3 glasses prepared by the sol-gel process. This short paper reports, for the first time, up-conversion emission in Nd3+ doped SiO2 based sol-gel glasses. Following the conventional sol-gel process [8], tetraethylorthosilicate (TEOS) was diluted in ethanol (EtOH) and water, with HCl added as a catalyst. The mole ratio of TEOS to EtOH to H2O was 1 : 8 : 8. The solution was allowed to a hydrolyze at 60 ◦C for an hour. Al(NO3)3·9H2O and Nd(NO3)3·6H2O were used as the precursors of Al2O3 and Nd2O3 respectively. They were dissolved in EtOH in separate beakers and then added drop-by-drop into the pre-hydrolyzed TEOS solution. The end solutions were stirred at room temperature in a sealed bottle for a period of one week. Dried gels were thus obtained by removing the cover of the bottle and leaving the gel in the open air for several days. A high temperature treatment was carried out on all these dried gels in an electric furnace at 1000 ◦C for about 12.5 h, and were kept there for about 5 h, and then cooled down to room temperature gradually. Based on our previous results on the laser transition (F3/2→ I11/2) properties at 1064 nm of Nd3+ doped Al3+ co-doped silica [9], we have analyzed three samples for upconversion emissions at various Nd3+ concentrations. The mole ratio of each of the chemicals used was as follows: 100SiO2 : 10AlO1.5 : xNdO1.5 (x = 0.1, 0.5 and 1.0). The up-conversion emission spectra were measured by using a Spex Fluorolog-3 spectrofluorometer, attached with a 1934D3 phosphorimeter. This system employs the Datamax software package for acquiring the spectrum and the decay curve data. The source of excitation was a xenon flash lamp. The measured data pertaining to the luminescence were corrected for the detector. Fig. 1 shows the up-conversion emission spectra of the three samples studied under excitation at 580 nm. An intense violet emission peak at 399 nm has been observed in all these samples. Three additional weaker fluorescent transitions at 342 nm, 372 nm and 452 nm have also been found. Referring to the energy diagram of Fig. 2, the emissions correspond to transitions: D3/2 → I9/2 (∼342 nm), D3/2 → I11/2 and