Co-doped Silica Research Articles

High efficiency energy transfer in Ce,Tb co-doped silica prepared by sol-gel method

Amorphous Ce,Tb co-doped silica (SiO2) was prepared using the sol-gel method with the aim of studying the energy transfer from Ce to Tb ions. It was initially found that adding Ce reduced the Tb emission intensity, implying that energy transfer did not occur. In fact, the Ce single doped sample exhibited very poor emission. Ultraviolet-visible diffuse reflectance measurements displayed the signature of non-luminescent Ce4+ rather than Ce3+ ions. We therefore annealed the samples in a reducing atmosphere of 4% hydrogen in argon gas at 1000°C. The reduced Ce single doped samples exhibited bright luminescence and the diffuse reflectance measurements now showed the characteristic of Ce3+ ions. The reduced Ce,Tb co-doped samples excited at the Ce absorption wavelength gave characteristic Tb emission (with negligible Ce emission), indicating that very efficient energy transfer from Ce to Tb was achieved. For samples containing 1mol% Tb, the maximum luminescence was found when co-doping with 0.5mol% Ce. Using such co-doped silica samples exhibiting energy transfer, it is possible to obtain effective luminescence from the Tb3+ ions via excitation of Ce3+ ions at 325nm, instead of exciting the Tb3+ ions directly which requires a shorter wavelength of about 227nm.

Theoretical analysis of characteristics for 2 μm Tm3+:Ho3+ co-doped silica fiber laser pumped by a 1550 nm fiber laser

We established a theoretical model of 2μm Tm3+:Ho3+ co-doped silica fiber laser pumped by a 1550nm fiber laser based on the rate-equation theory and performed the numerical simulation using Runge–Kutta algorithm and Newton–Raphson algorithm. The intracavity power distributions of both pump and laser of the Tm3+:Ho3+ co-doped silica fiber laser based on the Tm3+:Ho3+ co-doped silica fiber supplied by the National Optics Institute in Canada (NOIC) were obtained. The effects of the output reflectivity R4(λs) at the output laser wavelength λs and the concentrations of Tm3+ and Ho3+ in the fiber on laser output performance were analyzed. In order to achieve a high laser output power, the optimal R4(λs) of 0.13 was verified and the optimal Tm:Ho ratio of 1:2.4 was proposed. Finally, better output performance for the fiber laser based on the optimized Tm3+:Ho3+ co-doped silica fiber was obtained than the laser using the fiber supplied by the NOIC. This theoretical model and numerical simulation results will guide the fabrication of 2μm Tm3+:Ho3+ co-doped all-fiber lasers pumped by 1600-nm-band (1500–1750nm) Er3+:Yb3+ co-doped silica fiber lasers.

Upconversion luminescence in Tm3+/Yb3+ co-doped double-clad silica fibers under 980 nm cladding pumping

An investigation is reported of the visible and near-infrared upconversions in Tm3+/Yb3+ co-doped double-clad silica fibers (TYDFs) under excitation at 980 nm. The TYDFs used were fabricated using the modified chemical vapor deposition (MCVD) and solution doping techniques. Three distinct upconversion luminescences were observed at wavelengths of 482, 649 and 816 nm and their intensities found to increase with Yb3+ concentration. The intensity of blue and red fluorescence bands at 482 and 649 nm were found to be the highest with LTY-8 fiber, which had Tm3+ and Yb3+ concentrations of 5.6 × 1019 and 15.5 × 1019 ions/cc, respectively. The upconversion luminescence intensity was also observed to decrease with an increase in temperature. The main emission switched from 482 nm to 816 nm as the temperature increased above 200°C.

Formation of an extended CoSi2 thin nanohexagons array coherently buried in silicon single crystal

A Co-doped silica film was deposited on the surface of a Si(100) wafer and isothermally annealed at 750 °C to form spherical Co nanoparticles embedded in the silica film and a few atomic layer thick CoSi2 nanoplatelets within the wafer. The structure, morphology, and spatial orientation of the nanoplatelets were characterized. The experimental results indicate that the nanoplatelets exhibit hexagonal shape and a uniform thickness. The CoSi2 nanostructures lattice is coherent with the Si lattice, and each of them is parallel to one of the four planes belonging to the {111} crystallographic form of the host lattice.

Al3+/Eu2+共掺杂高硅氧玻璃的荧光特性

Al³⁺/Eu²⁺共掺杂高硅氧玻璃的荧光特性

Photoluminescence from Er3+ ion and SnO2 nanocrystal co-doped silica thin films

Er3+ ions embedded in silica thin films co-doped by SnO2 nanocrystals are fabricated by sol-gel and spin coating methods. Uniformly distributed 4-nm SnO2 nanocrystals are fabricated, and the nanocrystals showed tetragonal rutile crystalline structures confirmed by transmission electron microscope and X-ray diffraction measurements. A strong characteristic emission located at 1.54 μm from the Er3+ ions is identified, and the influences of Sn doping concentrations on photoluminescence properties are systematically evaluated. The emission at 1.54 μm from Er3+ ions is enhanced by more than three orders of magnitude, which can be attributed to the effective energy transfer from the defect states of SnO2 nanocrystals to nearby Er3+ ions, as revealed by the selective excitation experiments.

Luminescence of Yb2+, Yb3+ co-doped silica glass for white light source

Yb2+, Yb3+ co-doped silica glasses were prepared by solid state reaction under vacuum condition for the first time. The luminescence properties of Yb2+-doped silica glass were investigated. There are four strong absorption bands in the Ultraviolet (UV) light region due to the 4f14–4f135d1 transition of the Yb2+ ions. The main emission wavelength of the Yb2+-doped silica glass was around 530nm by the excited wavelength of 398nm. The full width at half maximum (FWHM) of the excitation and emission bands were 137nm, 165nm respectively. The results suggest the Yb2+-doped silica glasses may be the potential medium for white light sources based on near UV LED chip.

FITC and Ru(phen)3 2+ co-doped silica particles as visualized ratiometric pH indicator

The performance of fluorescein isothiocyanate (FITC) and tris(1, 10-phenanathroline) ruthenium ion (Ru(phen)32+) co-doped silica particles as pH indicator was evaluated. The emission intensity ratios of the pH sensitive dye (FITC) and the reference dye (Ru(phen)32+) in the particles were dependent on pH of the environment. The changes in emission intensity ratios of the two dyes under different pH could be measured under single excitation wavelength and readily visualized by naked eye under a 365-nm UV lamp. In particular, such FITC and Ru(phen)32+ co-doped silica particles were identified to show high sensitivity to pH around the pKa of FITC (6.4), making them be potential useful as visualized pH indicator for detection of intracellular pH micro-circumstance.

Detection of Moisture in Oil Using Evanescent Absorption from Sapphire Optical Waveguide Coated with Co-Doped Silica Film

We present a device that facilitates the measurement of moisture in oil or organic solvents. The device exploits the absorption of the evanescent waves from an optical waveguide to measure changes in the absorption spectra of CoCl2-doped thin films on sapphire. We fabricate a thin film from silica sol solution and find that the addition of Triton-X 100 facilitates the fabrication of a water-sensitive film. We discuss the conditions for adding Triton-X 100 and for the heat treatment and report on the state of the thin film from measurements using a DIC microscope, powder XRD, and a SEM.

Development of Metal-doped Silica Membranes for Increased Hydrothermal Stability and Their Applications to Membrane Reactors for Steam Reforming of Methane

Hydrothermal stability is one of the most important technical challenges for hydrogen separation silica membranes. Metal doping into silica matrix was proposed, and it was found that Ni and Co were effective to improve the hydrothermal stability. Co-doped silica membranes showed a high permeance of 1.8 × 10−7 mol/(m2 · s · Pa) and H2/N2 permeance ratio of 730 with hydrothermal stability (500 °C, steam partial pressure 300 kPa). Using hydrothermally stable silica membranes, permeation properties of helium, hydrogen and water vapor were examined based on the activation energy of permeation. The activation energy of H2 permeation correlated well with the permeance ratio of He/H2. The permeance ratios of H2/H2O of silica membranes are always larger than unity, although the kinetic diameter of hydrogen (0.289 nm) is larger than that of water (0.265 nm). Silica membranes were applied to bimodal catalytic membranes, which consisted of microporous silica top layer for selective permeation of hydrogen and a bimodal catalytic support layer where catalysts such as Ni were impregnated inside a bimodal support consisting of mesopores (γ-alumina) and macropores (α-alumina). Increased performance for production of hydrogen was confirmed by catalytic membranes for steam reforming of methane.

ゾル－ゲル法による多孔質シリカ膜の細孔径制御法と耐水蒸気性

Sol-gel derived silica membranes are reviewed in terms of control of silica network size and hydrothermal stability, which are most important issues for a practical application of amorphous silica membranes in industry. For control of silica network size, organic-template and spacer methods are introduced. Bridged alkoxides with organic groups between 2 Si atoms can be used for control of silica network size by both template and spacer method, for example, BTESE-derived silica membranes showed quite high hydrogen permeance with high H2 to SF6 permeance ratio of 1,000 due to loose organic-inorganic silica networks by Si-C-C-Si unit. For hydrothermal stability of amorphous silica membranes at high temperatures, metal-doped silica membranes are introduced, especially Ni- and Co-doped silica membranes with superior hydrothermal stability and hydrogen permeation performance. Finally, recent progresses in metal-doped silica membranes such as Nb-SiO2 and Pd-SiO2 are also summarized.

希土類-リン共ドープシリカガラスのゾル-ゲル合成と発光特性

希土類-リン共ドープシリカガラスのゾル-ゲル合成と発光特性

Theoretical modelling of dual-wavelength pumpedYb3 + –Tm3 + co-doped silica fibre laser

Numerical simulations have, for the first time to our knowledge, been carried out to characterize theYb3 + –Tm3 + co-doped silica fibre laser (YTFL), defined by a fibre grating and an end mirror, by usingthe rate equations, which take into consideration both the energy transfer processes fromYb3 + toTm3 + ions and the cross-relaxation processes among differentTm3 + ions. A dual-wavelength pumping scheme with one at 805 nm and the other at 975 nm is usedto pump the YTFL. We have investigated the wavelength-dependent output power ofthe YTFL, from 1750 to 2200 nm, which takes its maximum output power at ∼ 1800 nm. The effect of the cross-relaxation processes in theTm3 + -doped silica fibre laser has been studied. The results indicate that these processes are beneficialto the laser and should be considered in the theoretical modelling. The influence of theYb3 + concentration on the characteristics of the YTFL has also been analysed and the results show thatYb3 + dopants can improve the output power and slope efficiency of the laser.

ChemInform Abstract: Excitation of Er3+ Emission in Er, Yb Codoped Thin Silica Films.

Abstract Effects of Yb codoping on photoluminescence of Er 3+ ions at room temperature in SiO 2 films thermally grown on silicon are investigated. We demonstrate that for an excitation wavelength of 488 nm Yb ions act as efficient sensitizers of the 4 I 13/2 – 4 I 15/2 emission of Er 3+ ions. We have found that for the fixed dose of Yb the Er 3+ intensity is directly proportional to the Er concentration. Models of the mechanisms responsible for sensitization are discussed. It is shown that the Yb/Er concentration ratio of 0.5–2 is optimum for the dopant densities of 2–4×10 20 cm −3 .

Spectral characteristics of the erbium-bismuth co-doped silica fibers and its application in single frequency fiber laser

We developed two kinds of erbium (Er)-bismuth (Bi) co-doped silica fibers with different erbium doping concentrations. After investigation of its spectral characteristics, it was found that the co-doping of the bismuth could alleviate the clustering of the erbium ions in the silica fiber and thus improve the fluorescence efficiency. However, the near-infrared (NIR) fluorescence spectrum attributed to the bismuth ions was different from that reported before and needs further comprehensive investigation. For the heavy Er doped erbium-bismuth (Er-Bi) co-doped fiber (about 8000 ppm Er concentration), the optical absorption coefficients at the wavelengths of 976 and 1530 nm are more than 40 and 90 dB/m, respectively. A couple of fiber Bragg gratings with proper reflectivity were chosen to be spliced to 2 cm long of this fiber forming a compact linear cavity fiber laser. Upon the excitation of the 976 nm laser diode, stable single frequency fiber laser operation was realized with a maximum side mode suppression ratio more than 60 dB and a line-width less than 1 kHz. By splicing a segment of the Er fiber to the output end of the fiber laser, the fiber laser worked in a master oscillator pumping amplifier (MOPA) structure and emitted an increased laser power of more than 100 mW.

Controllable preparation and fluorescence properties of Y 3+ and Eu 3+ co-doped mesoporous silica

The controllable preparation and forming mechanism of rare-earth Y 3+ and Eu 3+ chemically co-doped fluorescent mesoporous silica were studied in detail. Their structures, morphologies, chemical compositions and emission properties were characterized and evaluated by small angle X-ray scattering, nitrogen adsorption/desorption measurements, high resolution transmission electron microscopy, inductive coupled plasma-atomic emission, X-ray photoelectron spectra and fluorescent spectroscopy. The results show that chemical composition of the resultant mesoporous materials were significantly affected by solution acidity condition, and can be effectively adjusted by varying the feed ratio of raw materials at a suitable solution acidity condition. These materials with a well-ordered two-dimensional hexagonal mesoporous structure and high specific surface area exhibit significantly broadened emission band from 526 to 682 nm and the fluorescent emission mechanism and influence of materials structure on optical properties were investigated.

Brillouin spectroscopy of Nd–Ge co-doped silica fibers

Abstract The effect of Nd-doping on both the longitudinal acoustic velocity and material damping coefficient (Brillouin spectral width) of silica fiber are measured. We find that Nd-doping results in anomalously large changes in the acoustic properties of SiO2, such as that material damping is greatly exacerbated by the incorporation of Nd. We find that the spectral width increases by about 151% per wt% of Nd2O3 (for small [Nd]). This is very large compared to the effect of Ge-doping, as observed in this work. This may result from poor coordination in the SiO2/GeO2 matrix, and may be considerably different with the use of co-dopants such as Al that tend to improve the solubility of the rare earths. The acoustic velocity is found to decrease at a rate of about 6.1% per wt% of Nd2O3.

Visible and near infra-red up-conversion in Tm^3+/Yb^3+ co-doped silica fibers under 980 nm excitation

The spectroscopic properties of Tm(3+)/Yb(3+) co-doped silica fibers under excitation at 980 nm are reported. Three distinct up-conversion fluorescence bands were observed in the visible to near infra-red regions. The blue and red fluorescence bands at 475 and 650 nm, respectively, were found to originate from the (1)G(4) level of Tm(3+). A three step up-conversion process was established as the populating mechanism for these fluorescence bands. The fluorescence band at 800 nm was found to originate from two possible transitions in Tm(3+); one being the transition from the (3)H(4) to (3)H(6) manifold which was found to dominate at low pump powers; the other being the transition from the (1)G(4) to (3)H(6) level which dominates at higher pump powers. The fluorescence lifetime of the (3)H(4) and (3)F(4) levels of Tm(3+) and (2)F(5/2) level of Yb(3+) were studied as a function of Yb(3+) concentration, with no significant energy back transfer from Tm(3+) to Yb(3+) observed.

Investigation on the spectral characteristics of bismuth doped silica fibers

We investigated the fluorescence characteristics of the bismuth doped silica fibers with and without Al co-dopant which are fabricated by means of modified chemical vapour deposition (MCVD) technique. It was found that the bismuth and germanium codoped silica fiber exhibited a strong broad infrared emission centring at 1450 nm and covering 1300 nm when excited by the laser diodes working at 808 nm and 976 nm respectively. It was also found that for the Al and bismuth codoped silica fiber, the red (centring around 750 nm) and the infrared fluorescence (centring around 1100 nm) may originate from different emission centers in the fiber. Furthermore, strong up-conversion luminescence was also observed in both Al codoped and non-Al codoped bismuth doped fibers when the fibers were excited by an acoustic-optic Q-switched Nd:YVO 4 laser. It is thus concluded that the upper energy level absorption reported in the work of the bismuth doped silica fiber lasers may result from the fluorescence emission sites not responsible for the infrared emission.

Highly efficient upconversion emission and luminescence switching from Yb 3+/Tm 3+ co-doped water-free low silica calcium aluminosilicate glass

We present highly efficient 480 and 800 nm upconversion emissions in Tm 3+/Yb 3+ co-doped water-free low silica calcium aluminosilicate glass under excitation at 976 nm. As a result of this efficient upconversion process, a luminescent switching with the excitation intensity has been observed. The switching is explained and discussed using rate equations analysis and saturation effects. By means of fitting of the experimental data point, it was possible to obtain the value of the energy transfer parameter related to the transition 2F 5/2, 3H 4→ 2F 7/2, 1G 4. The value of this parameter is higher than that of materials like YLF. This switching mechanism could be used in the development of sensors and networks for optical processing and optical communications.