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Abstract: Tellurite glass is proposed as a host for broadband erbium-doped fiber amplifiers because of their excellent optical and chemical properties. A new single mode Er3+/Yb3+ codoped tellurite fiber with D-shape cladding geometry is fabricated in this work. When pumped at 980nm, a broad erbium amplified spontaneous emission (ASE) nearly 100nm in the wavelength range of 1450–1650nm around 1.53μm is observed. It was found that the emission spectrum from erbium in tellurite glass fibers is almost twice as broad as the corresponding spectrum in tellurite bulk glass. The changes in ASE with regard to fiber lengths and pumping power were measured and discussed. The output of about 2.3mW from Er3+/Yb3+ codoped tellurite fiber ASE source is obtained under the pump power of 700mW. The broad 1.53μm emission of Er3+ in Er3+ /Yb3+ codoped tellurite glass fiber can be used as host material for potential broadband optical amplifier and tunable fiber lasers. [Copyright &y& Elsevier]

Abstract: The effects of F− ions on physical and spectroscopic properties of the Yb3+ in tellurite glass system are investigated. The results show that the glass system takes on good thermal stability with the content of ZnF2 lower than 15mol%, both the emission cross-section and the fluorescence lifetime of Yb3+ ions increase evidently which indicate that such oxyfluoride tellurite glass system is a promising laser host matrix for high power generation. FT–IR spectra were used to analyze the effect of F− ions on the structure of tellurite glasses and OH− groups in this glass system. Analysis demonstrates that addition of fluoride decreases the symmetry of the structure of tellurite glasses which increases the emission cross-section and removes the OH− groups, and which improves the measured fluorescence lifetime of Yb3+ ions. [Copyright &y& Elsevier]

Nonradiative decay of 4I13/2→4I15/2 transition of Er3+ has been investigated in a series of oxide glasses. For Er3+-doped glass samples, the Judd–Ofelt analysis on absorption spectra was performed and the fluorescence lifetime was determined by extrapolating to zero Er3+ concentration limit. Infrared spectra were measured in order to investigate the influence of OH− groups in different glasses. The effects of glass matrix on the decay rate were discussed from the viewpoint of phonon energy, variations of effective fields, and OH− groups. Compared to other glasses, phosphate glass presents low quantum efficiency and large nonradiative decay rate due to its high phonon energy and hygroscopic behavior. [Copyright &y& Elsevier]

The effect of radiative trapping on measurement of the spectroscopic properties of Yb3+-doped phosphate glasses was investigated as a function of Yb3+ concentration at different thicknesses. It was found that radiative trapping exists generally in Yb3+:phosphate glasses, even at low concentration. As a result, the measured lifetime of Yb3+ in phosphate glasses is usually larger than the calculated one. The maximum discrepancies between them at high concentration are found to be <42%. The calculated lifetime should be used as a reference in determining the true value of the measured lifetime because of it being lengthened largely by radiative trapping. On the other hand, the shape of fluorescence spectrum exhibits remarkable changes due to the radiative trapping. What is more, the intensity increase of Δλeff at high concentration is greater than that of low doping. The Δλeff increases 36% from 53 to 72 nm with thickness increasing from 0.3 to 4 mm at 6 mol% Yb2O3 content, while Δλeff increases only 11% when Yb2O3 content was fixed at 0.2 mol%. [Copyright &y& Elsevier]

Abstract: The B2O3 component was introduced into Er3+/Ce3+ co-doped TeO2–ZnO–Na2O–Nb2O5 glass to improve energy transfer rate of Er3+:4I11/2→Ce3+:2F5/2 phonon-assisted cross-relaxation process. With the 6mol% substitution of B2O3 for TeO2, the energy transfer rate increased from 1300 to 1831s−1 and the fluorescence intensity increased by about 13.4%. However, the more B2O3 substitution in the same glass system reduced the quantum efficiency of Er3+:4I13/2→4I15/2 transition due to the higher OH− group concentration. The results show that an appropriate amount of B2O3 component can be used to improve the phonon-assisted energy transfer rate and enhance 1.53μm fluorescence emission by increasing the phonon energy of host glass. The effect of B2O3 on the energy transfer process, the lifetimes of the 4I11/2 and 4I13/2 levels, and the upconversion emission have also been investigated. [Copyright &y& Elsevier]

Abstract: A series of Tm3+/Yb3+ co-doped lanthanum–zinc–lead–tellurite (TPZL) glasses pumped by a 980nm laser diode (LD) were demonstrated to obtain a high efficiency of infrared-to-visible upconversion. Effects of PbO content on the thermal stability, structure and upconversion properties of Tm3+/Yb3+ co-doped TPZL glasses had been investigated. The efficient visible upconversion fluorescences corresponding to the 1G4→3H6, 1G4→3F4 and 3H4→3H6 transitions of Tm3+ were observed under 980nm excitation. The upconversion intensities of blue, red and near infrared emissions in Tm3+/Yb3+ co-doped TPZL glasses were obviously enhanced with increasing PbO content. The dependence of upconversion intensities on excitation power and the possible upconversion mechanisms had been evaluated by a proper rate equation model. Population density in different levels and coefficients of the energy transfer rate CDi (i=2, 4, 6) between Tm3+ and Yb3+ were estimated by fitting the simulated curves to the measured ones. The obtained three energy transfer coefficients CD 2, CD 4, and CD 6 were determined to be 5.7×10−17, 1.3×10−16 and 8.6×10−17 cm3/s, respectively. [Copyright &y& Elsevier]

The upconversion properties and mechanism of Er3+ ions have been studied for lead oxyfluorosilicate glasses containing Er2O3 concentrations from 0.2 to 2 mol%. Under 975 nm excitation, four emission bands centered at 411, 525, 543, and 655 nm corresponding to the 2H9/2→4I15/2, 2H11/2→4I15/2, 4S3/2→4I15/2, and 4F9/2→4I15/2 transitions of Er3+ ions, respectively, were simultaneously observed at room temperature. The bright green and red emissions are due to a two-photon upconversion process while the weak blue emission is determined by a three-photon upconversion process. Raman spectrum indicates that fluoride ions in the formation of glass network have important influence on upconversion luminescence of Er3+ in lead oxyfluorosilicate glasses. The intense upconversion luminescence of Er3+-doped lead oxyfluorosilicate glasses may be a potentially useful material for developing upconversion optical devices. [Copyright &y& Elsevier]

Abstract: Up-conversion luminescence and energy transfer (ET) processes in Nd3+–Yb3+–Er3+ triply doped TeO2–ZnO–Na2O glasses have been studied under 800nm excitation. Intense green up-conversion emissions around 549nm, which can be attributed to the Er3+: 4S3/2→4I15/2 transition, are observed in triply doped samples. In contrast, the green emissions are hardly observed in Er3+ singly doped and Er3+–Yb3+ codoped samples under the same condition. Up-conversion luminescence intensity exhibits dependence of Yb2O3-concentration and Nd2O3-concentration. Up-conversion mechanism in the triply doped glasses under 800nm pump is discussed by analyzing the ET among Nd3+, Yb3+ and Er3+. And a possible up-conversion mechanism based on sequential ET from Nd3+ to Er3+ through Yb3+ is proposed for green and red up-conversion emission processes. [Copyright &y& Elsevier]

Abstract: The Ce3+ ion was introduced into Er3+ doped TeO2–GeO2–Nb2O5–Li2O (TGNL) glass to improve the 1.5μm fluorescence characteristics. As increasing of Ce3+ concentration, the lifetime of Er3+:4I11/2 level is shortened form 360 to 225μs, while the Er3+:4I13/2 level remains unchanged. Accordingly, the upconversion fluorescence (blue, green and red) was quenched. Improved 1.5μm emission is obtained and the reason is ascribed to the increase of nonradiative rate between the 4I11/2 and 4I13/2 level of the Er3+ ions. [Copyright &y& Elsevier]

Abstract: The spectroscopic and fluorescent decay behaviors of Yb3+-doped SiO2–PbO–Na2O–K2O glass is reported in this work. Yb2O3 contents of 1, 1.5 and 2mol% are added into the glass. Through the measurement of absorption and fluorescence spectra, and fluorescent decay rate at room temperature and at low temperature (18K), it is found that the nonradiative decay rate of Yb3+ ions is mainly determined by the interaction between residual hydroxyl groups and Yb3+ ions. Concentration quenching effect can be omitted in this glass up to the Yb3+ ion concentration of 8.98×1020/cm3. Multiphonon decay rate is also very small because of the large energy gap between 2F5/2 and 2F7/2 levels of Yb3+ ions. [Copyright &y& Elsevier]

A series of new glasses of 70TeO2-(20-x) ZnO–xGeO2–5La2O3–2.5K2O–2.5Na2O (mol%) doped with Yb3+ is presented. Thermal analysis, spectra and laser properties of Yb3+ ions have been measured. It is found that 70TeO2–20GeO2–5La2O3–2.5K2O–2.5Na2O composition glass had better thermal stability than 75TeO2–20ZnO–5Na2O glass, higher stimulated emission cross-section of 1.23 pm2 for the 2F5/2→2F7/2 transition close to PN glass, lower minimum pump intensity of 0.98 KW/cm2, long fluorescence lifetime of 0.92 ms and the broad fluorescence effective line width of 77 nm. Evaluated from the good potential laser parameters, this system glass is a promising host of miniature solid lasers such as short pulse generation in diode pumped lasers, short pulse generation tunable lasers, high-peak power and high-average power lasers, etc. [Copyright &y& Elsevier]