[en] Yb³⁺-Er³⁺ co-doped Na₂O-GeO₂-PbO glass suitable for developing optical fiber lasers and amplifiers has been fabricated. The energy transfer efficiency from Yb³⁺ to Er³⁺ was investigated in the glasses with different Yb³⁺-Er³⁺ concentration ratios and the maximum energy transfer efficiency was found to be 67% at the Yb³⁺-Er³⁺ concentration ratio of 5:1. Subsequently, the studies of upconversion emissions in the visible range were performed. An intense green together with a relatively weak red emission was observed under the excitation of 976 nm diode laser. The quadratic dependence of the green emission on excitation power indicates that a two-photon absorption process occurs under a 976 nm excitation. However, for the red emission the slope of log-log plot of integrated intensity versus pump power declines with increasing Yb³⁺ ions content, indicating it is not resulted from a biphotonic process

[en] Highlights: • Microcrystals of lanthanide fluorides were prepared by sonication-assisted IL-based route. • It is a fast, simple, green and mild method to get lanthanide fluoride microcrystals. • The microcrystals are uniform, monodisperse, well-shaped and phase-pure. • IL served as reaction medium, fluoride source as well as template. • Sonication helped to accelerate reaction and get monodisperse uniform microcrystals. - Abstract: We introduce an ionic liquid-based method for the synthesis of uniform lanthanide fluoride microcrystals with the assistance of a sonication-accelerated reaction system. It is a fast, simple and mild process to get uniform monodisperse spherical lanthanide fluoride microcrystals in large scale. Homogeneous precipitation in a biphasic system of ethanol solution of lanthanide nitrates and ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate [C_4mim][PF_6] led to the uniform LnF_3 microcrystals. The method was applied to the preparation of pure LnF_3 (Ln = La, Ce, Pr, Nd) and Eu"3"+-doped LaF_3, Tb"3"+-doped CeF_3. SEM images indicated highly uniform cotton-like spherical microcrystals were obtained. HRTEM image indicated that the microcrystals were aggregated by nanocrystals of 6–10 nm due to agglomeration effect of the ionic liquid. The uniformity and dispersility of LaF_3 decreased with the increasing of the molar ratio of [C_4mim][PF_6] to La(NO_3)_3·6H_2O. Diameter of the microcrystal decreased from La to Nd. Photoluminescence properties of Eu"3"+-doped LaF_3 and Tb"3"+-doped CeF_3 were also studied

[en] A series of new glasses of 70TeO₂-(20-x) ZnO-xWO₃-5La₂O₃-2.5K₂O-2.5Na₂O (mol %) doped with Yb³⁺ is presented. Thermal stability and spectroscopic properties of Yb³⁺ ions have been measured. It found that 70TeO₂-15WO₃-5ZnO-5La₂O₃-2.5K₂O-2.5Na₂O composition glass had better thermal stability ((T_x-T_g)>160 deg. C) than 75TeO₂-20ZnO-5Na₂O glass, high-stimulated emission cross-section of 1.32 pm² for the ²F_5/2→²F_7/2 transition and existed measured fluorescence lifetime of 0.93 ms and the broad fluorescence effective linewidth of 74.5 nm. Evaluated from the good potential laser parameters, this system glass is promising for miniature solid fiber lasers or high-peak power and high-average power lasers, also for wave-guides or tunable lasers

[en] Er³⁺-doped heavy metal oxyfluoride germanate glass suitable for developing potential optical amplifiers and upconversion lasers has been fabricated and characterized. Under 975 nm excitation, intense and broad 1533 nm infrared fluorescence and visible upconversion fluorescence were observed. For 1533 nm emission band, the full width at half maximum (FWHM) is 57 nm, the fluorescence lifetime is 5.7 ms, and the quantum efficiency is ∼100%. Efficient 529, 551, and 657 nm upconversion emissions correspond to the transitions ²H_11/2→⁴I_15/2, ⁴S_3/2→⁴I_15/2, and ⁴F_9/2→⁴I_15/2, respectively. Raman spectrum indicates the important role of fluoride ions in the formation of glass network. The dependence of upconversion intensities on excitation power involves two-photon absorption processes for the three emission bands. The possible upconversion mechanisms are discussed based on the energy matching conditions and the quadratic dependence on excitation power

[en] The green and red upconversion luminescence of Er³⁺ in lead chloride tellurite glasses excited at 980 nm is investigated. Three intense emission bands centered at 530, 545, and 658 nm corresponding to the transitions ⁴S_3/2→⁴I_15/2, ²H_11/2→⁴I_15/2 and ⁴F_9/2→⁴I_15/2, respectively, were simultaneously observed at room temperature. With increasing PbCl₂ content, the intensity of green (530 nm) emissions increase slightly, while the green (545 nm) and red (658 nm) emissions increase significantly. The results indicate that PbCl₂ has more influence on the green (545 nm) and red (658 nm) emissions than the green (530 nm) emission. The dependence of upconversion intensities on excitation power and possible upconversion mechanisms are discussed and evaluated

[en] 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 ²H_9/2→⁴I_15/2, ²H_11/2→⁴I_15/2, ⁴S_3/2→⁴I_15/2, and ⁴F_9/2→⁴I_15/2 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

[en] A Tm³⁺-doped silica-germanate was successfully prepared by high-temperature melting method in this work and compared with traditional silicate and germanate glasses comprehensively. The DSC results indicated a better ability against thermal damage (higher T_g=636 °C) compared with silicate glass together with better thermal stability (ΔT=106 °C and S=3.17) than germanate (ΔT=99 °C and S=2.64) glass. Intense 1.8 μm emission in the silica-germanate glass was also obtained when pumping by an 808 nm laser diode, which possessed larger peak absorption and emission cross section (3.15×10^–21 cm² and 7.08 ×10^–21 cm²). Finally, the structure analysis suggested a low phonon energy and high rare earth ions solubility in silica-germanate glass through Raman spectra and X-ray photoelectron spectroscopy. All results indicate that the prepared silica-germanate glass is a promising candidate for 2 μm laser applications.

[en] 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 ²F_5/2→²F_7/2 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

[en] In this paper, Er³⁺ doped Y₂O₃ and Nb₂O₅ modified germanate glasses possessing good thermal stability are reported. On the basis of absorption spectra and Judd–Ofelt theory, a detailed investigation of Judd–Ofelt intensity parameters (Ω_2,4,6) and radiative properties is carried out. Moreover, emission cross section at 2.7 μm is calculated based on Füchtbauer–Ladenburg equation and compared with other Er³⁺ doped glass systems. A reasonable energy transfer mechanism is proposed. It is interesting that the emission cross section and radiative transition probability in 5 mol% Nb₂O₅ modified germanate glass are much larger than those with 5 mol% Y₂O₃. Results indicate that present germanate glasses along with excellent 2.7 μm spectroscopic performance might have potential application for mid-infrared fiber laser. Highlights: • Er³⁺ doped Y₂O₃ and Nb₂O₅ modified germanate glasses were prepared. • The investigated samples possess superior thermal property. • Judd–Ofelt parameters and radiative properties are calculated and analyzed. • Large emission cross section and high radiative probability at 2.7 μm are achieved. • A reasonable energy transfer mechanism is proposed

[en] Er³⁺ doped Y₂O₃ and Nb₂O₅ modified germanate glasses have been reported which possesses excellent thermal stability. Near infrared emission characteristics upon excitation of a conventional 980 nm laser diode have been investigated. According to absorption spectra and refractive index, Judd–Ofelt intensity parameters, spontaneous radiative transition probabilities, radiative lifetimes and stimulated emission cross sections have been calculated and discussed. These results indicate that the predicted spontaneous transition probability and emission cross section of Er³⁺:⁴I_13/2→⁴I_15/2 transition in developed glasses can reach as large as 192.39 s⁻¹ and 7.14×10⁻²¹ cm², respectively. Hence, germanate glasses with superior performances might be a useful material for applications in optical amplifiers around 1.53 μm. - Highlights: • Er³⁺ doped Y₂O₃ and Nb₂O₅ modified germanate glasses were prepared. • The thermal stability and spectra properties were investigated. • The developed glasses possessed superior stability. • The stimulated emission cross-sections were calculated and discussed