Spectroscopic Properties and Effect of Radiation Trapping of a New Er^(3+)/Yb^(3+) Co-Doped Tellurite-Silicate Glasses

A new serials of Er^3＋/Yb^3＋ co-doped tellurite-silicate glasses were prepared by the technique of high-temperature mehing. The thermal stability, absorption spectra, emission spectra and upconversion spectra were measured and investigated. It is found that these kinds of glasses have good thermal stability, broad FWHM and large stimulated emission cross-section. The three upconversion emission at 525, 546, 658 nm, corresponding to the ^2H11/2→^4Ⅰ15/2, ^4S3/2→4^Ⅰ15/2 and ^F9/2→^4Ⅰ15/2 transitions of Dr^3＋ ions,

Thermal stability and Judd-Ofelt analysis of optical properties of Er^(3+)-doped tellurite glasses

Er3＋-doped TeO2-ZnO-Na2O-B2O3-GeO2 （TZNBG） glasses were prepared by melt-quenching method. Differential scanning calorimetry （DSC） and thermal mechanical analysis （TMA） were used to calculate thermal parameters： crystallization temperature （Tx）, glass transition temperature （Tg） and thermal expansion （α）. Besides, Judd-Ofelt theory is applied to analyzing absorption spectra. Intensity parameters -λ （λ=2, 4, 6）, transition probabilities Aed, radiative lifetime τi, and branching ratios β of Er3＋ transitions were obtained. Emission cross-section σemis of 4I13/2→4I15/2 transition of Er3＋ was calculated according to the theory of McCumber. All of the parameters indicate that the thermal stability and optical properties of Er3＋-doped TZNBG glasses are improved effectively.

Three-color upconversion luminescence of rare earth codoped oxyhalide tellurite glasses

The red, green, and blue upconversion properties of Er^3＋/Tm^3＋/Yb^3＋-codoped oxyhalide tellurite glasses were studied under 980 nm LD excitation. The intense red （657 nm）, green （530 and 545 nm）, and blue （476 nm） emissions were simultaneously observed at room temperature. The results showed that the mixed halide modified tellurite glass （TZFCB） had strong upconversion emissions. The effect of halide on upconversion intensity was observed and discussed, and possible upconversion mechanisms were evaluated. The intense red, green, and blue upconversion luminescence of Er^3＋/Tm^3＋/Yb^3＋-codoped oxyhalide tellurite glasses might be a potentially useful material for developing three-dimensional displays applications.

Investigation on Upconversion Luminescence of Tm^(3+)/Yb^(3+)-Codoped Oxychloride Tellurite Glasses

Tm^3 ＋/Yb^3 ＋-codoped oxychloride tellurite glasses were prepared. Thermal stability, Raman spectra and upconversion luminescence spectra were studied, and upconversion luminescence mechanisms were analyzed. The results show that the intense blue and relatively weak red emissions centered at 476 and 649 nm corresponding to the transitions ^1G4→^3H6 and ^1G4→^3H4 of Tm^3＋ , respectively, were simultaneously observed at room temperature under 980 nm LD excitation. With increasing while PbCl2 content, thermal stability of host glasses increases, phonon energy of host glasses decreases, and upconversion luminescence intensities increase, which indicate that Tm^3＋/ Yb^3＋-codoped oxychloride tellurite glasses can be used as potential host materials for upconversion blue lasers.

Upconversion properties of Er^3＋/Yb^3＋ co-doped TeO2-Nb2O5-Li2O glasses

The Er^3＋/Yb^3＋ co-doped TeO2-Nb2O5-Li2O glass is prepared by conventional melting method, and its upconversion spectra are measured. The intense green upconversion luminescence upon excitation with a 976 nm laser diode is observed with the naked eyes. The dependence of luminescence intensity on the ratio of Yb^3＋/Er^3＋ is discussed in detail, and the relationship between the ratio of green luminescence intensity to red luminescence intensity and the ratio of Yb^3＋/Er^3＋ is also studied, The luminescence intensity increases with the ratio of Yb^3＋/Er^3＋ increasing. The ratio of Yb^3＋/Er^3＋ plays a more important role than the concentration of Er^3＋ in determining the upconversion luminescence intensity. The ratio of green luminescence intensity to red luminescence intensity reaches a maximum when ratio of Yb^3＋/Er^3＋ is 3. Thus the glass could be one of the potential candidates for LD pumping solid-state lasers.

Spectral and Lasing Properties of Er^(3+0/Yb^(3+) Co-Doped Phosphate Glasses Pumped by LD

Er^3 ＋/Yb^3 ＋ phosphate glasses were fabricated. According to McCumber theory, the stimulated emission cross-section of Er^3＋ ions at 1533 nm was calculated on the basis of absorption spectrum, and 0.84 × 10^-20 cm^2 is derived, the fluorescence lifetime of ^4I13/2 level is 8.5 ms. An Er^3＋/Yb^3＋ co-doped phosphate glass CW laser pumped by LD was demonstrated at room temperature. The maximum output power is 80 mW and slope efficiency is 16.5%.

Spectroscopic properties of Yb^(3+)-doped TeO_2–BaO–BaF_2–Nb_2O_5-based oxyfluoride tellurite glasses

A series of oxyfluoride glasses with the compositions of 75 mol% TeO2, 10 mol% Nb2O5, （15 mol%-x） BaO, x BaF2 （x =0 mol%, 5 mol%, 10 mol%, 15 mol%） doped with Yb2O3 were prepared by the melt-quenching method. Their emission cross-sections, fluorescence lifetimes, and gain properties were investigated by using the absorption spectra and the fluorescence decay curves. The results show that by substituting BaF2 for BaO, the emission cross-section decreases from 1.37 pm^2 to 1.21 pm^2, and the fluorescence lifetime increases from 0.71 ms to 0.96 ms. These properties indicate that this oxyfluoride tellurite glass may have potential uses as the Yb2O3-doped gain medium in a solid laser.

Spectroscopic Properties of Nd^(3+)-Doped Tellurite Glasses

The Nd^3＋-doped pared. The absorption and tellurite glasses were preemission spectra of Nd^3 ＋- doped tellurite glasses at room temperature were measured. The Judd-Ofelt parameters （Ω2, Ω4, Ω6） of the glasses were calculated from measured absorption spectra. The calculation results of luminescence properties （A, β, τrad, σ） of Nd^3＋ ions in the tellurite were glasses were given. Spectroscopic properties, concentration quenching in these kinds of the glasses were investigated. The results indicate that the tellurite glasses with composition of 70% TeO2, 20% ZnO, （ 10 - x ） % La2O3, x % Nd2O3 （ mol% ） show high emission cross section and low phonon energy. The fluorescent intensity and the emission cross section have a maxi- mum value at x = 0.5, namely, the optimum Nd^3 ＋ ion concentration in the tellurite glass is 0.5% （1.93 × 10^20 ions·cm^-3）. The fluorescence properties of Nd^3＋ measured are basically in accord with the calculated results.

Thermal Stability and Raman Scattering Spectra of Tellurite Glasses for Broadband Fiber Raman Amplifiers

The glass transition temperature （T）, crystallization onset temperature （T） and Raman scattering spectra of new tellurite glasses were studied as the function of glass composition. With the introduction of other metal oxides such as Nb2O5, BaO and WO3, T temperature increases, the intensity of exothermal peaks decreases, and thermal stability of tellurite glass improves. It was found that more TeO3 units transformed into TeO4 units and non-bridging oxygen atoms decreased with the incorporating other metal oxides in glassy network, when the content of TeO2 was fixed. Appearance of peak at 920 cm^-1 broadens the Raman bandwidth of tellurite glasses, which is very useful realize high efficient broadband fiber Raman amplifiers.

Preparation of AgCl Nano-Crystal Embedded Tellurite Nonlinear Optical Glasses under Electric Field Accompanied Heat Treatment

The quantum effect of nano-crystals is an important factor to improve nonlinear optical performance of nanocrystal embedded glasses, while controlling the size distribution and content of nano-crystals in the glass accurately is a key to obtain good quality. The auxiliary direct current electric field, accompanied with heat treatment, was applied on AgCI containing niobic tellurite glass sheet. The nucleation and crystallization of the glass were well controlled under auxiliary electric field. It was found that the average size of AgCI nano-crystal particles in the glass is smaller than that under single heat treatment, and the content of nano- crystals is higher. Therefore the third-order nonlinear optical performance of the glass was increased a lot. The local-area distributed AgCl nano-crystal particles can also be embedded into a glass sheet by using locally applied electric field.

Influence of Coordinate Field Index on Upconversion Luminescence in Er ^(3+) Doped Tellurite Glasses

The upconversion luminescence in Er 3+ doped tellurite glasses (MKT: TeO_2-MgO-K_2O) were performed. Two green emission bands at 521 and 550 nm, corresponding to the 2H_ 11/2→4I_ 15/2 and 4S_ 3/2→4I_ 15/2 transitions, respectively, were observed. Coordinate field index, which was proposed by deducing from Pauling′s rules on the basis of Zachariasen′s random network theory, can be used to rationalize the remarkable variation in the intensity of upconversion luminescence.

Raman Scattering Study on Vibrational Modes and .Structure of Lanthanum Tellurite Glasses

Raman spectra of xLa203-（1-x）TeO2 （x=0, 0.05, 0.10, 0.15, 0.20, and 0.25） lanthanum tellurite glasses were measured and analyzed over the entire glass-forming region in an effort to quantitatively follow the structural changes caused by lanthanum oxide variation. For the first time, systematic intensity measurements have been performed to elucidate the composition induced structural changes in tile high-frequency stretching vibration region and a possible mechanism was proposed. The network structure of the glasses is formed by mixing TeO4 trigonal bipyramid and Te03 trigonal pyramid units. The change of the lanthanum oxide content results in conversion of the TeO4 units to TeO3 units with a varying number of non-bridging oxygen atoms. Analysis of the Raman band contours in terms of vibrations due to different oxygen bridged trigonal bipyramid and trigonal pyramid tellurite structural units, allowed to calculate the relative amounts of the species involved in the structural changes with composition. The fraction of the terminal oxygen atoms has been estimated from the Raman intensities with the aid of a structural model concerning the structure of tellurite network systems. The simulation of the experimental density of lanthanum tellurite glasses with modifier content up to 25% revealed that the short range order building units assumed here are sufficient to account for the overall structure in these glasses.

Infrared-to-green upconversion properties of Er^(3+)/Yb^(3+) co-doped TeO_2-TiO_2-K_2O glasses upon excitation with 976 nm lasers diode

The energy transfer and upconversion of Er 3+ /Yb 3+ co-doped TeO2-TiO2-K2O glasses upon excitation with 976nm lasers diode were studied. The tellurite glasses were prepared by conventional melting methods. Their optical properties and sensitization upconversion spectra were performed. The dependence of green upconversion luminescence intensity on the mole ratio of Yb 3+ to Er 3+ and Er 3+ concentration were discussed in detail. When the mole ratio of Yb 3+ to Er 3+ is 25/1 and Er 3+ concentration is 0.1% （mole fraction）, or when the mole ratio of Yb 3+ to Er 3+ is 10/1 and Er 3+ concentration is 0.15%, the optimal upconversion luminescence intensity is obtained. The obtained glasses can be one of the potential candidates for lasers-diode pumping microchip solid-state lasers.

Up-conversion photoluminescence characteristics of Yb^(3+):Er^(3+):Tm^(3+) co-doped borosilicate glasses

Yb^3＋：Er^3＋：Tm^3＋co-doped borosilicate glasses are prepared. Their strong up-conversion photoluminescence spectra in a range from ultra-violet to near-infrared, which are excited by a 978-nm laser diode, are measured, and the mechanisms of energy transfer among Yb^3＋ Er^3＋ and Tm^3＋ ions are discussed. The results show that there is an unexpected wavelength at 900-nm emission from Yb^3＋ Stark splitting levels to pump Tm^3＋ ions and there exists an optimum pump power. The concentration of the Tm^3＋ dopant gives rise to a prominent effect on the intensity of visible and near-infrared emissions for the yb^3＋：Er^3＋：Tm^3＋ co-doped borosilicate glasses.

Investigation on energy transfer from Er^(3+) to Nd^(3+) in tellurite glass

A study of energy transfer of Er^3＋/Nd^3＋ codoped tellurite glasses was presented. By Nd^3＋ co-doping, both the Er^3＋ green emission corresponding to the Er^3＋： （^4S3/2, ^2H11/2）→^4I15/2 transitions and the red emission corresponding to the Er^3＋： ^4F9/2→^4I15/2 transitions were quenched. The energy transfer mechanism between Er^3＋ and Nd^3＋ was discussed based on their energy level characteristics. The interaction parameters, CO-A, for the energy transfer processes from Er^3＋ to Nd^3＋ in tellurites glass were calculated. Finally, the resonant transfer Er^3＋： ^4I9/2→Nd^3＋： （^4F5/2, ^2H9/2） was proposed to be the most probable microscopic process to occur in contrast with the other processes.

1.3 μm Emission from Nd^(3+)-doped Tellurite Glass Fiber

1 wt pct Nd2O3-doped tellurite bulk glass and fiber with the same composition of 75TeO2-15ZnO-5Na2O-5Li2O4(mol fraction, %) were fabricated. Judd-Ofelt analysis was carried out for the bulk. The emission from the 4F3/2→4I13/2 transition in fiber is at 1.33 μm wavelength with a spectral bandwidth of 55 nm, which is similar to that in bulk. In the case of the fiber, the lifetime of 4F3/2 Ievel is 164 μs, and the quantum efficiency is -100%. The figure-of-merit for gain (<δpTo) for Nd3+-doped tellurite glass is about 2.8×10-24 cm2·S, which is quite comparable vvith that in Nd3+-doped fluoroaluminate glasses, and is an order of magnitude larger than Pr3+-doped fluoride glasses.

Optical temperature sensor based on up-conversion fluorescence emission in Yb^(3+):Er^(3+) co-doped ceramics glass

yb^3＋：Er^3＋ co-doped oxy-fluoride ceramics glass has been prepared. The mechanism of up-conversion emissions about Er^3＋ was discussed, and the temperature properties of green up-conversion fluorescence between 303 and 823 K were investigated. The results show that the sensitivity of this sample reaches its maximum value, about 0.0047 K^-1, when the temperature is 383 K, indicating that this kind of sample can be used as high temperature and high sensitivity optical temperature sensor.

Preparation and ASE Spectrum of a Single-Mode Erbium Doped Tellurite Glass Fiber with D-type Cladding Geometry

Based on the host of tellurite glasses, the glass formation, preform manufacture, and fiber fabrication are described. The characterization of amplified spontaneous emission (ASE) from this newly fabricated single-mode Er3+-doped tellurite fibers is also presented. When pumped at 980 nm, a very broad erbium ASE around 1.53 μm was observed. The variations of ASE with fiber length and pumping power are measured and discussed. The output of 2 mW from Er3+-doped tellurite fiber ASE source was obtained under the pump power of 660 mW.

Tm^(3+)-doped tellurite glass with Yb^(3+) energy sensitized for broadband amplifier at 1400–1700 nm bands

A kind of novel experiment was disclosed as it possessed two bands of fluorescence emission at 1.4 and 1.6 μm, which were perfectly complimentary to the current C band of optic communication. The fluorescence was based on energy transfer and up-conversion processes between Tm^3＋ and Yb^3＋ under direct pumping of 975 nm LD. The spectra and lifetimes of Tm^3＋ fluorescence in the tellurite glass were described. The corresponding fluorescence characteristics and energy migration process were analyzed by the method of lifetime and intensity comparison. The mechanism of the up-conversion based IR fluorescence was presented upon analyzing the multi-photon pumping process. The potential advantages of Tm^3＋/Yb^3＋ co-doped tellurite glass as amplifier material were concluded.