A Single-Frequency Linearly Polarized Fiber Laser Using a Newly Developed Heavily Tm3+-Doped Germanate Glass Fiber at 1.95 μm

A compact linearly polarized, low-noise, narrow-linewidth, single-frequency fiber laser at 1950nm is demonstrated. This compact fiber laser is based on a 21-mm-long homemade Tm3＋-doped germanate glass fiber. Over 100-mW stable continuous-wave single transverse and longitudinal mode lasing at 195Ohm are achieved. The measured relative intensity noise is less than -135dB/Hz at frequencies over 5 MHz. The signal-to-noise ratio of the laser is larger than 72dB, and the laser linewidth is less than 6kHz, while the obtained linear polarization extinction ratio is higher than 22 dB.

Structure and Luminescence Properties of Eu^(3+) Doped SiO_2 Glass Synthesized by Sol-Gel Process

Under different annealing temperatures, Eu 3+ doped SiO 2 gel and glass were prepared by sol gel method, and the structure and luminescent properties were studied with excitation spectra, emission spectra, IR and DTA TG. The results show that the fluorescent intensity tends to get stable when concentration of Eu 3+ doped is above 1 86 % (mass fraction) most water absorbed by the gel was removed at 300 ℃, and that the emission spectrum of Eu 3+ , with peaks at 614, 588, 577 nm, is due to 5D 0→ 7F 2, 5D 0→ 7F 1, 5D 0→ 7F 0 transitions, and the excitation peaks at 318, 362, 380, 393, 412 and 462 nm were observed. These results illustrate that the temperature range of 300～500 ℃ is critical for the structure conversion from gel to glass, and the fluorescence is strongly quenched by water.

High Quantum Efficiency and High Concentration Erbium-Doped Silica Glasses Fabricated by Sintering Nanoporous Glasses

A new method was used to prepare erbium-doped high silica （SiO2 % 〉 96 % ） glasses by sintering nanoporous glasses. The concentration of erbium ions in high silica glasses can be considerably more than that in silica glasses prepared by using conventional methods. The fluorescence of 1532 nm has an FWHM （Full Wave at Half Maximum） of 50 nm, wider than 35 nm of EDSFA （erbium-doped silica fiber amplifer）, and hence the glass possesses potential application in broadband fiber amplifiers. The Judd-Ofelt theoretical analysis reflects that the quantum efficiency of this erbium-doped glass is about 0.78, although the erbium concentration in this glass （6 × 10^3） is about twenty times higher than that in silica glass. These excellent characteristics of Er-doped high silica glass will be conducive to its usage in optical amplifiers and microchip lasers.

Photoinduced Second Harmonic Generation of Bi_2S_3 Microcrystallite Doped Silica Glass

Silica glasses doped with Bi2S3 microcystallite was prepared by the sol-gel process. Photoinduced second harmonic generation (SHG) was observed in the glass when it was irradiated with intense 1.06 mum and frequency doubled laser beams from a mode-locked Nd: YAG laser. It was found that the signal intensity increased with the irradiating time and approached a saturation gradually. The effect may be explained reasonably by the DC field model.

Properties of Local Structure Surrounding Eu^(3+)Ion in Various Niobate-Silicate Glasses

A Series of niobate silicate glasses doped with Eu 3+ ions were prepared. The emission, phonon side band spectra, fluorescence line narrowing spectroscopy and fluorescence lifetimes in these glasses were studied. The intensity parameters and crystal field parameter of Eu 3+ were obtained. The results indicate that the intensity ratio of the electric dipole to magnetic dipole transition and the intensity parameter Ω 2 increase with the increasing concentration of Nb 2O 5, indicating that the symmetry becomes lower, the Eu O bonds become stronger and the covalency of Eu O bond increases. The value of B 20 decreases with the increasing concentration of Nb 2O 5, indicating that the distance between the Eu 3+ ion and oxygen decreases and the Eu O bond becomes strong, corresponding to the results of the former. As the concentration of Nb 2O 5 increases, the electron phonon coupling becomes stronger, thus the nonradiative transition rate of 5D 0 becomes larger and the lifetime of 5D 0 becomes shorter.

Dielectric properties and relaxation dynamics in PbF_2-TeO_2-B_2_O3-Eu_2O_3 glasses

Frequency and temperature dependent dielectric dispersion of 20PbF2？20TeO2？（60？x）B2O3？xEu2O3（x=0 to 2.5, mole fraction, %） glasses prepared by the melt？quenching technique were investigated in the frequency range 1 Hz？10 MHz and temperature range 313？773 K. Dielectric relaxation dynamics was analyzed based on the electric modulus behavior. Dielectric losses （tanδ） are found to be negligibly small in the temperature range 313？523 K, proving good thermal stability of the glasses. The present Eu2O3-doped oxyfluroborate glasses showed low dielectric loss at higher frequency and lower temperature, proving their suitability for nonlinear optical materials.

Effect of Network Modifiers on Spectroscopic Properties of Erbium-doped Phosphate Glasses

The integrated absorption cross section Σ abs, peak emis sion cross section σ emi, Judd-Ofeld intensity parameters Ω t(t=2,4,6), and spontaneous emission probability A R of Er 3+ ions were determined fo r Erbium doped alkali and alkaline earth phosphate glasses. It is found the comp ositional dependence of σ emi is almost similar to that of Σ abs, wh ich is determined by the sum of Ω t (3Ω 2+10Ω 4+21Ω 6). In addition, the compositional dependence of Ω t was studied in these glass systems. As a resu lt, compared with Ω 4 and Ω 6, the Ω 2 has a stronger compositional depend ence on the ionic radius and content of modifiers. The covalency of Er-O bonds in phosphate glass is weaker than that in silicate glass, germanate glass, alumi nate glass, and tellurate glass, since Ω 6 of phosphate glass is relatively la rge. A R is affected by the covalency of the Er 3+ ion sites and correspon ds to the Ω 6 value.

Sol-Gel Derived SiO_2-Y_2O_3∶Eu^(3+) Nanocomposites and Their PL Properties

An improved sol-gel method was used to prepare Eu3+ ions doped SiO-Y2O3 nanocomposites. Systematic study on the effect of post-annealling treatment on photoluminescence (PL) properties of the samples under various europium ions doping concentrations were carried out. XRD patterns indicate that the samples show an amorphous matrix structure, and the SEM patterns show that the samples present a multi-hole loosen structure, and a rod structure after high-temperature annealling treatment (800 ℃) for 3 h. Raman spectra demonstrate that Y3+ and Eu3+ ions were incorporated into the composites successfully through the sol-gel and post-anneal process. Under the excitation of 387 nm (7F0→5G2) violet light (but not 394 nm (7F0→5L6)), the strongest emission spectrum, the red light, was observed at around 616 nm (5D0→7F2) when the samples were re-treated by annealing at high temperature after 3 months laying aside. Without annealing treatment, the optimized doping mole ratio of Eu ions is about 9%, which is much higher than that doped in SiOglass with the concentration of 3.5%, and it then becomes 5% when the samples are treated by high temperature annealing. In addition, the excitation of 532 nm (7F0→5D1) light can also arouse a comparatively strong emission.

Experimental investigation of photolunlinescence spectra of Yb^(3+) sensitized Er^(3+)-doped glass samples in series

Fabrication technology of the Yb3+:Er3+ co-doped glass samples is introduced. Photolummescence (PL) characteristics of a single sample were experimentally investigated. The PL peak intensities of two samples in series were measured and discussed. The results show that the PL peak intensities of two samples in series depend on pump manners and arrangement of the samples. The better amplification ability can be obtained by two samples in series doped with low-concentration ytterbium instead of a single sample doped with high-concentration ytterbium.

Rare Earth Doped Glass Waveguide Amplifiers

Progress in rare earth doped planar glass waveguide devices has been significant over the past few years. The history and applications of these devices are reviewed.

Near-white light-emitting Dy^(3+)-doped transparent glass ceramics containing Ba_2LaF_7 nanocrystals

Glass ceramics Ba2LaFT：xDy3＋ are obtained through the conventional melt-quenching technique, and their lu- minescent properties are investigated. Under 350 nm excitation, the emission spectra consists of a strong blue- yellow band as well as a weak red emission centered at 660 nm, which are attributed to the 4F9/2 →6H15/2, 4F9/2→6H13/2 and 4F9/2 → 6Hll/2 transitions of the Dy3＋ ion, respectively. The corresponding Commission Internationale de L＇Eclairage （CIE） chromaticity coordinate for a sample of 2 mol.% Dy203 after being heat-treated at 690℃ is （0.313, 0.328）. It is concluded that the formed materials may have the possibility of applications for white light-emitting diodes （LEDs）.

A downshifting Eu^3+doped glass embedded with concave pyramid microstructure to improve the efficiency of silicon solar cell

The average photoelectric conversion efficiency(PCE)of a bare mono crystalline silicon solar cell is 14.71%±0.03%under AM1.5.It decreases to 14.20%±0.005%when covering an un-doped flat glass on the solar cell,and it goes down to 14.10%±0.005%by using a 5 wt%Eu^3+doped glass.The absorptions of the Eu^3+doped CPM glass one-to-one match the excitation spectra at 362,381,393,400,413 and464 nm,which are related to the transitions of 7 F0→(5 D4,5 G2,5 L6,5 D3),7 F1→5 D3,and 7 F0→5 D2,respectively.In addition,a concave pyramid microstructure(CPM)is embedded in the glass surface to increase light transmittance.The average PCE increases to 14.61%±0.07%when a 5 wt%Eu^3+doped CPM glass covers on the silicon solar cell.Compared with the un-doped flat glass,a net increase of the PCE is0.41%,where the 0.16%increment of PCE is from the lighting trapping of the CPM structure,and the downshifting of near ultraviolet(NUV)light by Eu^3+ion donates the other 0.25%increment.It confirms that the as-prepared Eu^3+doped CPM glass has a good downshifting and antireflection function.

Thermal stability and optical properties of a novel Tm^(3+) doped fluorotellurite glass

A series of fluorotellurite glasses based on（81–x）Te O2-（10＋x）KF-9La2O3（TKL）, where x=0 mol.%, 5 mol.%, 10 mol.%, 15 mol.%, doped with 2000 ppm Tm2O3, were prepared by the conventional melt quenching method.The influence of KF content on the thermal stability and optical spectroscopic properties of the Tm3＋ doped fluorotellurite glasses were investigated by differential scanning calorimetry（DSC）, X-ray diffraction（XRD）, density measurement, Fourier transform infrared spectroscopy（FTIR）, UV-VIS-NIR optical spectroscopy and fluorescence spectroscopy.Judd-Ofelt intensity parameters of Tm3＋ in as-prepared glasses were determined and used to calculate the spontaneous emission probabilities and the radiative lifetime for the 4f-4f transitions of the Tm3＋ ions.Stimulated emission cross sections in the 1470 nm region（σse） were evaluated by Füchtbauer-Ladenburg formula.The results showed that KF substitution of Te O2 was beneficial to improving the thermal stability, decreasing glass density and reducing the content of OH related groups for the investigated fluorotellurite glasses.The glass with composition of 66 Te O2-25KF-9La2O3（named TKL25） had the longest radiative lifetime of the 3H4（361 μs） and the largest FWHM×σse value（420.07×10–28 cm3）, which made it a promising material for S-band fiber amplifiers.

Energy transfer mechanism in Er^(3+) doped fluoride glass sensitized by Tm^(3+) or Ho^(3+) for 2.7-μm emission

Enhanced 2.7 μm emission is obtained in Er3＋/Tma＋ and Era＋/Ho3＋ codoped ZBYA glasses. Absorp- tion and emission spectra are tested to characterize the 2.7 μm emission properties of Era＋/Tm3＋ and Era＋/Ho3＋ doped ZBYA glasses and a reasonable energy transfer mechanism of 2.7 μm emission between Er3＋ and Tm3＋Ho3＋） ion is proposed. Codoping of Tm3＋ or Ho3＋ significantly reduces the lifetime of the Era＋： 4I13/2 level due to the energy transfer of Er3＋：4I13/2 →Tm3＋：3F4 or Er3＋：4I13/2 →Ho3＋： 5I7. Thus, the 2.7μm emission is strengthened and the 1,5μm emission is decreased accordingly especially in the Era＋/Tma＋ sample. The upconversion effects between the Er3＋/Tm3＋ and Er3＋/Ho3＋ doped ZBYA glasses are different attribute to the different energy transfer efficiencies. Both of the two codoped samples possess nearly equal large emission cross section （16.6 × 10 -21 cm-2） around 2.7 μm. The results indicate that this Er3＋/Tm3＋ or Er3＋/Ho3＋ doped ZBYA glass has potential applications in 2.7 μm laser.

Thermal and structural properties of Nd2O3-doped calcium boroaluminate glasses

Nd^3＋ doped CaO-Al2O-B2O3-CaF2 glasses were prepared by conventional melt-quenching technique,and their structural and thermal properties were studied.The amorphous nature of these samples was confirmed by X-ray diffraction（XRD）.The measured density showed an increase with Nd2O3 doping,at the expense of CaO.Raman spectra presented changes with addition of Nd2O3,which indicated that the network structure of the glasses studied presented various borate groups,such as tetraborates,metaborates,ortho-borates and pyroborates units.The N4 values calculated from FTIR spectra revealed that incorporation of Nd2O3 into glass network converted the structural units from BO4 to BO3.From the analysis of DTA curves,we verified that Tg increased with the addition of Nd2O3;it was similar to the behavior caused by modifier oxides in the structure of borate glasses.Besides that,the calculated glass stability Tx–Tg for doped samples presented a decrease if compared to the undoped glass.Specific heat and thermal conductivity did not present significant changes with Nd2O3 concentration,up to 2.30 mol.%.The results of density,DTA,Raman and FTIR reinforced the idea that Nd2O3 acted as network modifier.

Effect of Ultrashort Pulsed Laser and X-Ray Irradiation on Au^+ -Doped Glass

Au nanoparticles were precipitated inside Au+-doped glass samples after irradiation by femtosecond laser or x-ray. Femtosecond laser and X-ray irradiation result in decreasing of anneal temperature and critical size for the precipitation of Au nanoparticles.

Dual-wavelength Bi2Se3-based passively Q-switching Nd3+-doped glass all-fiber laser

We demonstrate a dual-wavelength passively Q-switched Nd^（3＋）-doped glass fiber laser using a few-layer topological insulator Bi2Se3 as a saturable absorber（SA） for the first time, to the best of our knowledge. The laser resonator is a simple and compact linear cavity using two fiber end-facet mirrors. The SA is fabricated by Bi2Se3/polyvinyl alcohol composite film. By inserting the SA into the laser cavity, a stable Q-switching operation is achieved with the shortest pulse width and maximum pulse repetition rate of 601 ns and 205.2 kHz,respectively. The maximum average output power and maximum pulse energy obtained are about 6.6 mW and 38.8 nJ, respectively.

Strong upconversion luminescence in Er^(3+)/Yb^(3+)-doped halide modified tellurite glass

Upconversion luminescence of Er3+/Yb3+-doped halide tellurite glass is investigated experimentally upon 976-nm excitation. Three intense emissions centered at 525, 545 and 655 nm owing to the transitions 2H11/2-4I15/2, 4S3/2 -4I15/2 and 4F9/2-4I15/2, respectively, are observed when pumping power is as low as 20 mW. The upconversion mechanisms and power dependent intensities are discussed. The high-populated 4I11/2 level is supposed to serve as the intermediate state responsible for the upconversion processes.

Photoanode Activity of ZnO Nanotube Based Dye-Sensitized Solar Cells

Vertical ZnO nanotube （ZNT） arrays were synthesized onto an indium doped tin oxide （ITO） glass substrate by a simple electrochemical deposition technique followed by a selective etching process. Scanning electron microscopy （SEM） showed formation of well-faceted hexagonal ZNT arrays spreading uniformly over a large area. X-ray diffraction （XRD） of ZNT layer showed substantially higher intensity for the （0002） diffraction peak, indicating that the ZnO crystallites were well aligned with their c-axis. Profilometer measurements of the ZNT layer showed an average thickness of -7 μm. Diameter size distribution （DSD） analysis showed that ZNTs exhibited a narrow diameter size distribution in the range of 65-120 nm and centered at -75 nm. The photoluminescence （PL） spectrum measurement showed violet and blue luminescence peaks that were centered at 410 and 480 nm, respectively, indicating the presence of internal defects. Ultra-violet （UV） spectroscopy showed major absorbance peak at ,-348 nm, exhibiting an increase in energy gap value of 3.4 eV. By employing the formed ZNTs as the photo-anode for a dye-sensitized solar cell （DSSC）, a full-sun conversion efficiency of 1.01% was achieved with a fill factor of 54%. Quantum efficiency studies showed the maximum of incident photon-to-electron conversion efficiency in a visible region located at 590-550 nm range.

Concentration and annealing effect on PL properties of sol-gel derived SiO_2-Y_2O_3:Eu^(3+) nanocomposites

An improved sol-gel method was employed to prepare Eu3+ ions doped SiO2-Y2O3 nanocomposites.Systematic study was carried out on the effect of post-annealing treatment on photoluminescence(PL) properties of the samples under various europium ions doping concentrations.X-ray diffraction(XRD) patterns indicated that the samples showed an amorphous matrix structure,and the scanning electron microscopy(SEM) pictures showed that the samples presented a nano size(from 21 to 42 nm) granular-stack structure after hi...