Codoped Tellurite Glasses Research Articles

Thermally enhanced cooperative energy-transfer frequency upconversion in terbium and ytterbium doped tellurite glass

Infrared-to-visible frequency upconversion through cooperative energy-transfer and thermal effects in Tb3+/Yb3+-codoped tellurite glasses excited at 1.064μm is investigated. Bright luminescence emission around 485, 550, 590, 625 and 655nm, identified as due to the 5D4→7FJ (J=6, 5, 4, 3, and 2) transitions of the terbium ions, respectively, was recorded. The excitation of the 5D4 emitting level of the Tb3+ ions is assigned to cooperative energy-transfer from pairs of ytterbium ions. The effect of temperature on the upconversion process was examined and the results revealed a fourfold upconversion enhancement in the 300–500K interval. The enhancement of the upconversion process is due to the temperature dependence of the Yb3+-sensitizer absorption cross-section under anti-Stokes excitation. A rate-equation model using multiphonon-assisted absorption for the ytterbium excitation combined with the energy migration effect between Yb–Yb pair and Tb3+ ground-state depopulation via multiphonon excitation of the 7FJ excited states describes quite well the experimental results.

The luminescence of Er3+,Yb3+,Tm3+-codoped tellurite glass pumped at 970nm

The fluorescence and up-conversion spectrum of Er3+/Yb3+, Tm3+/Yb3+, Er3+/Yb3+/Tm3+-codoped tellurite glasses pumped by a 970nm laser diode has been studied. The lifetimes of Er3+:4I11/2 and Er3+: 4I13/2 levels have been measured. It is found that the fluorescence width in the range of 1450—1700nm in Er3+/Yb3+/Tm3+-codoped tellurite glass has been broadened clearly. There is a fluorescence peak at 1630nm which is probably due to Tm3+:1G4→3F2 transitions in Er3+/Yb3+/Tm3+-codoped tellurite glass. Up-conversion phenomena exist in all the three kinds coped tellurite glasses because of its lower phonon energy of host. The addition of Tm3+ in Er3+/Yb3+-codoped tellurite glasses quenches the up-conversion efficiency of Er3+:4S3/2 green and Er3+:4F9/2 red emissions. The quenching effect is due to the energy transfer between Er3+ and Tm3+, especially the cross-relaxation process among them.

Multi-Rare-Earth Ions Codoped Tellurite Glasses for PotentialDual Wavelength Fibre-Optic Amplifiers

A novel co-doping method of multi-rare-earth (RE) ions was demonstratedin tellurite glasses for fibre amplifiers. Fluorescence emissions atboth 1.53 and 1.63 µm communication windows were firstly observed fromEr3+/Yb3+/Tm3+-codoped tellurite glasses under asingle wavelength pumping at 980 nm. The full width at half maximum offluorescence at 1.53 and 1.63 µm are 55 nm and 50 nm,respectively. This codoping method of three RE ions could be applied toother low photon energy glasses, which would be possibly used forpotential dual wavelength fibre-optic amplifiers to broaden thecommunication windows.

Emission Properties of Tm3+-Ln3+(Ho3+,Tb3+,Eu3+) Co-Doped Tellurite Glasses by Energy Transfer.

Generally, it is difficult for 1.4μm band amplification to form population inversion between the initial 3H4 and the terminal 3F4 levels in Tm3+, because lifetime of the initial level is shorter than that of the terminal level. Accordingly emission properties and lifetimes of tellurite glasses co-doped with Tm3+ and various rare earth ions (Ho3+, Tb3+ and Eu3+) were investigated in order to improve the population inversion by co-doping method. These co-doped ions depopulated the terminal level rapidly by energy transfer from the terminal level to the co-doped ion. Especially, for the initial level, Ho3+ did not affect the population of the initial level because Ho3+ cannot easily cause cross-relaxation. Ho3+ had the largest effect on lifetime of the terminal level without decreasing the population of the initial level. Ho3+ showed the best performance among three investigated rare earth ions as a co-doped ion.

Time dependence and energy-transfer mechanisms in Tm 3+, Ho 3+ and Tm 3+–Ho 3+ co-doped alkali niobium tellurite glasses sensitized by Yb 3+

Glass samples with the composition (mol%) 80TeO 2–10Nb 2O 5–5K 2O–5Li 2O, stable against crystallization, were prepared containing Yb 3+, Tm 3+ and Ho 3+. The energy transfer and energy back transfer mechanisms in samples containing 5% Yb 3+–5% Tm 3+ and 5% Yb 3+–5% Tm 3+–0.5% Ho 3+ were estimated by measuring the absorption and fluorescence spectra together with the time dependence of the Yb 3+ 2 F 5/2 excited state. A good fit for the luminescence time evolution was obtained with the Yokota–Tanimoto's diffusion-limited model. The up-conversion fluorescence was also studied in 5% Yb–5% Tm, 5% Yb–0.5% Ho and 5% Yb–5% Tm–0.5% Ho tellurite glasses under laser excitation at 975 nm. Strong emission was observed from 1 G 4 and 3 F 2 Tm 3+ energy levels in all samples. The 5 S 2 Ho 3+ emission was observed only in Yb 3+Ho 3+ samples being completely quenched in Yb 3+/Tm 3+/Tm 3+ samples.

Energy transfer and 1.3 μm emission in Pr–Yb codoped tellurite glasses

To seek the possibility of an efficient 1.3 μm amplifier in oxide materials, the concentration and temperature dependence of fluorescence properties of the Pr 3+ : 1G 4 → 3H 5 at 1.3 μm and Yb 3+: 2 F 5/2 → 2 F 7/2 at 1 μm were investigated in codoped tellurite glasses with compositions of 75TeO 2–20ZnO–5Na 2O– xPr 2O 3– yYb 2O 3. By 0.97 μm pumping, the 1.3 μm emission of Pr 3+ was sensitized by the Yb → Pr energy transfer. The lifetime obtained by 1.02 μm emission of Yb 3+ at room temperature was concentration quenched with the presence of only 0.1 mol% Pr 2O 3. The energy transfer efficiency from Yb to Pr in a codoped glass was found to be more than 90% even in the glass of [Yb]/[Pr]>100. With increasing temperature, the Yb-lifetime in singly doped glass increased and that in codoped glass decreased. These results can be explained by assuming rapid energy migration between Yb ions and promotion of Yb 3+ : 2 F 5/2 → Pr 3+: 1 G 4 transfer at higher temperature.

Energy transfer from Tm 3+: [formula omitted] to Dy 3+: [formula omitted] in oxyfluoride tellurite glasses

Thermal analysis and optical properties indicate that Tm 3+ and Dy 3+ co-doped oxyfluoride tellurite glasses can be excellent candidates for fiber amplifiers at 1.47 μm region. Substitution of GeO 2 and In 2O 3 in tellurite glasses increased the glass stability without decreasing the lifetime of the upper Tm 3+: 3 H 4 level, and the fluoride substitution increased lifetime of excited energy levels of Tm 3+ ion. Dy 3+ co-doping in the Tm 3+-doped oxyfluo⋮appride tellurite glasses enhanced the depopulation of the Tm 3+: 3 F 4 level through an energy transfer Tm 3+: 3 F 4 →Dy 3+: 6 H 11/2 . We report the measurements of crystallization, glass transition temperatures, and optical properties of Tm 3+, Dy 3+ co-doped oxyfluoride tellurite glasses.

Compositional Dependence of Infrared‐to‐Visible Upconversion in Yb3+‐ and Er3+‐Codoped Germanate, Gallate, and Tellurite Glasses

Upconversion fluorescences of the green 4S3/2→4I15/2 and red 4F9/2→4I15/2 transitions of the Er3+ ion are studied for Yb3+‐ and Er3+‐codoped sodium germanate, potassium tantalum gallate, and barium tellurite glasses by InGaAs laser‐diode pumping. The phonon energies of the host glasses are determined by infrared‐reflection measurements. Compositional effects on the Judd—;Ofelt parameters for the Er3+ ion, the spontaneous emission probability (SPE) of the 2F5/2→2F7/2 transition for the Yb3+ ion, and the phonon energy of the glass network are discussed in terms of glass structure. The factors that affect the upconversion fluorescence intensities of the Er3+ ion are discussed, using the phonon energy of the host glass and the SPE for the Yb3+ ion in the germanate, gallate, and tellurite glasses.

Mechanisms and concentration dependence of Tm 3+ blue and Er 3+ green up-conversion in codoped glasses by red-laser pumping

Tm 3+-Er 3+ codoped tellurite glasses were pumped at 650 nm and the up-conversion characteristics of Tm 3+ and Er 3+ luminescences were investigated. By Er 3+ codoping, the Tm 3+-460 nm up-conversion luminescence due to the 1D 2→ 3F 4 transition was quenched and the Tm 3+-480 nm up-conversion luminescence due to the 1G 4→ 3H 6 transition was selectively sensitized, due to which the intensity became more than 20 times larger than in the absence of Er 3+. Both Tm 3+-480 nm and Er 3+-550 nm up-conversion luminescence intensities have a maximum in the range where the ratio of Er 3+- to Tm 3+-content is about two. The result was discussed in the context of the energy transfer efficiency calculated from the lifetime of the Er 3+: 4I 13 2 level, the competition between the excited state absorption efficiency of Tm 3+: 1G 4← 3F 4 and the ground state absorption of Er 3+: 4F 9 2 ← 4I 15 2 estimated from the Judd-Ofelt analyses, and the concentration quenching of the Er 3+: 4S 3 2 level, mainly due to the cross relaxation. It is concluded that the small optimum ratio of the donor- to acceptor-content (≅2) should be ascribed to the specific mechanisms in the present sensitized up-conversion.

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1.47, 1.88 and 2.8 μm emissions of Tm3+ and Tm3+-Ho3+-codoped tellurite glasses

Tellurite glass is a good host for Tm3+ because of high quantum efficiency and good glass stability. For 1.47 μm the upper limit for Tm2O3 concentration without quenching is 0.4 wt%. For 1.88 μm, it should be 0.4 wt% in order to take advantage of the two-for-one transition.