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In this paper, Tm3+ doped pure tellurite glass, TiO2 modified tellurite glass and TiO2/GeO2 co-modified tellurite glasses were prepared. The effects of the introduction of TiO2 and GeO2 oxides on the thermal, structural, optical properties of tellurite glasses were compared and analyzed intensively. Besides, the Judd-Ofelt intensity parameters and absorption and emission cross sections were calculated. DTA curves indicated the thermal stability of pure tellurite glass enhance obviously by GeO2 modification. The introduction of TiO2 and GeO2 oxides in tellurite glasses arise a series of variation on the absorbance, luminescence peak position and fluorescence intensity which have been explained and analyzed in detail. Based on the analysis, the addition of TiO2 in tellurite glass contributes to the improvement of 2 μm fluorescence performance, and the introduction of GeO2 has great advantages in enhancing the thermal stability of glass.

In this paper, glasses and glass ceramics were prepared. Differential thermal analysis, X-ray diffraction and transmission electron microscopy were tested to study the structure. After heat treatment, 15–30 nm NaYF4 crystal phase was precipitated. It was found that the glass after heat treatment had stronger intensity of fluorescence emission than the glass without heat treatment. Besides, properly increasing the heat treatment temperature or time is beneficial to enhance the fluorescence intensity, lifetime and efficiency. The measured radiation lifetime and quantum efficiency of glass sample was 0.69 ms and 13.88%, which were smaller than those of glass-ceramics. The radiation lifetime and quantum efficiency of the glass-ceramic heat-treated at 625 °C for 4 h reached 1.65 ms and 22.51%. After comprehensive comparison, the performance of 2.0 μm luminescence reaches an optimum when it was heat treated at 625 °C for 4 h in this work.

The Tm3+/Ho3+ co-doped silicate-germanate glasses with good thermal properties were synthesized by high temperature melting method. 2.0 μm emissions with broad effective half-width (231.5 nm) were successfully obtained in present Tm3+/Ho3+ co-doped glasses without obvious quenching upon excitation of a commercial 808 nm laser diode. To further understand 2 μm fluorescence behaviors of the prepared glasses, energy transfer mechanism, efficiency, rate and microparameters from different levels of Tm3+ to Ho3+ ions have been obtained and discussed. In short, the Tm3+/Ho3+ co-doped silicate-germanate glass with excellent spectroscopic properties might be an attractive host material for 2 μm broadband solid laser.

An effective and facile “on-off” fluorescence sensing approach for the determination of Fe3+ ion using a large area and relatively uniform size graphitic carbon nitride nanosheets (GCNS) was developed. The prepared GCNS have blue and stable emission, as well as excellent water dispersion, and were applied as an effective fluorescent probe that based on the quenched fluorescence for selective and sensitive detection of Fe3+ ion. Herein, we explain the ambiguous fluorescence quenching mechanism between the GCNS and Fe3+, which mainly springs from the redox potential and empty d orbital of Fe3+. The redox potential and unfilled d orbit of Fe3+ endow it excellent binding force with GCNS, which generates most obvious fluorescence quenching effect with respect to other metal ions. The limit of detection (LOD) for Fe3+ was found to be about 2.06 μM. Therefore, the prepared GCNS has the potential to be used as a fluorescent probe for detection.

In this work, we have performed a comprehensive investigation of the Ag+ concentration effect on the morphological, thermal, structural, and mid-infrared emission properties of novel oxyfluoride borosilicate glasses and glass ceramics containing both Ag nanoparticles and erbium-doped hexagonal NaYF4 nanocrystals. The effect of Ag+ ions on the glass forming and crystallization processes was discussed in detail by glass structural analysis. It was found that the Ag+ concentration can affect the distribution of Na+ ion and bridge oxygen in boron-rich and silicon-rich phases, which induced the transformation between BO3 triangles and BO4 tetrahedra during crystallization process. In addition, there was a turning point when the doped Ag+ ion concentration reached its solubility in the borosilicate glass. Furthermore, the enhancement of the 2.7 μm emission and the reduction of the lifetime of the 4I13/2 level were observed both in glasses and in glass ceramics, and its origin was revealed by qualitative and quantitative analyses of the Er3+-Ag nanoparticles (localized electric field enhancement) and Er3+-Er3+ (nonradiative resonance energy transfer) interactions within glasses and glass ceramics. Moreover, the high lifetime of the 4I11/2 level (2.12 ms) and the peak emission cross section in 2.7 μm (6.8×10−21 cm2) suggested that the prepared glass ceramics have promising mid-infrared laser applications.

We report a detailed spectroscopic investigation of a series of fluorotellurite glasses with different Er3+ ions concentration in system 50TeO2-27BaF2-9ZnF2-8YF3-3MgF2-3NaF-xErF3-1HoF3(x = 1,2,3 mol%). Intense 2 μm emission and 2.75 μm emission with high absorption and emission cross-section were observed under 980 nm LD pumping, and the maximum gain coefficient around 2750 nm was as high as 2.41 cm−1, suggesting the prepared glasses are a competitive candidate for mid-infrared laser materials. Besides, it was found that the trend of 2 μm and 2.75 μm emission intensity varied with Er3+ ions concentration was different. Energy transfer process was discussed subsequently to explain this phenomenon. Furthermore, we quantitatively investigate the energy transfer efficiency from Er3+: 4I13/2 level to Ho3+: 5I7 level.

Tm 3+ /Ho 3+ doped tellurite glasses with good thermal stability and low phonon energy are prepared. 1.8 µm fluorescence, enhanced near 2 µm fluorescence and a weak 2.3 µm fluorescence are observed in the Tm 3+ /Ho 3+ co-doped glasses. The energy transfer mechanism between Tm 3+ and Ho 3+ has been analyzed according to the absorption spectra, the emission spectra and the level structures of Tm 3+ and Ho 3+ ions. The decay lifetime of 1.8 µm and 2 µm fluorescence in Tm 3+ /Ho 3+ co-doped tellurite glass are 0.38 ms and 2.46 ms, respectively. Moreover, the energy transfer efficiency between Tm 3+ : 3 F 4 and Ho 3+ : 5 I 7 levels is calculated and compared. Additionally, the calculated forward energy transfer coefficient C Tm-Ho is about five times as large as the reverse energy transfer coefficient C Ho-Tm . Results demonstrate that the Tm 3+ /Ho 3+ doped tellurite glass has excellent spectroscopic properties and can be an attractive candidate for 2 µm laser.

We constructed a core-shell like nanoarchitecture in Yb/Er ion and Yb/Ho SrTiO3 nanocrystal-codoped tellurite-borate glass. We demonstrated that the adverse energy transfer between Er3+ ions in the glass region and Ho3+ ions in the crystal region was effectively prohibited, which permits independent and highly efficient emission from Er3+ and Ho3+ ions.

International audience; Changes in glass structure and crystallization behaviour from oxyfluoride silicate glass to oxyfluoride germanate glass were studied by modifying the ratio of Si/Ge in oxyfluoride germanosilicate glass ceramics, and transparent glass ceramic with low light scattering and efficient mid-infrared emissions were obtained. The NaYF4 nanocrystals crystallization ability of oxyfluoride glass was decreased with the increase in Ge content, which can be attributed to the weakened oxide and fluoride phase separation in GeO2-rich glass. Upconversion and down-conversion emission spectra together with Ho3+: 5I6 energy level fluorescent decay curves have been discussed for SiO2-rich glass ceramics and GeO2-rich glass ceramics, in which the fluoride crystallization induced the decrease of multi-phonon non-radiative decay rates plays the main role in the energy transfer processes. The influence of Si/Ge ratio on 2 μm and 3 μm fluorescent emissions in glasses and glass ceramics, and its link with glass network structural changes were discussed. The optimized Yb/Ho codoped oxyfluoride germanosilicate glass ceramic with low light scattering, high peak emission cross section(11.18 × 10−21cm2) and maximum gain coefficient (1.387 cm−1) at 2888 nm provides a potential application in the development of new 3 μm laser devices based on transparent oxyfluoride glass ceramic materials.

Glass with the composition of SiO2-GeO2-CaCO3-Li2CO3-Nb2O5-BaO-Tm2O3 has been prepared and its characteristic temperatures have been measured. ΔT (155 °C) of the glass indicates it has good thermal stability. A broadband emission spectrum around 2 µm with full-width at half-maximum close to 237 nm has been obtained, which suggests this germanosilicate glass is a competitive candidate for the ultrashort pulse generation as few broadband emission realized by Tm3+ single-doping. The calculated maximum of absorption cross section and emission cross section of the transition Tm3+:3F4→3H6 was 3.31×10−21 cm2 at 1654 nm and 6.88×10−21 cm2 at 1870 nm, respectively. Besides, the energy transfer mechanism of 2 µm fluorescence behaviors was analyzed theoretically and quantitatively. The energy transfer coefficient CD-A of cross relaxation process of Tm3+ ions was 10.9×10−40 cm6/s in SGT glass. These results indicate that the prepared glass may have promising application in 2 µm fluorescence.

Tellurite glasses co-doped with Dy 3+ and Dy 3+ /Tm 3+ have been synthesized. Emission around 2.8 μm is successfully obtained in present glass upon excitation of a conventional 808 nm laser diode. Judd-Ofelt intensity parameters and radiative properties of Dy 3+ ions are calculated using the Judd-Ofelt theory. The luminescence characteristics and energy transfer mechanism are investigated and discussed. According to the absorption, fluorescence spectra and lifetime measurements, Tm 3+ ions can effectively absorb excitation and transfer their energy to Dy 3+ ions with high efficiency (up to 86.80%). Hence, the results demonstrate that Dy 3+ /Tm 3+ co-doped tellurite glasses possessing excellent spectroscopic properties is a potential medium for mid-infrared laser.

Correction for ‘Core–shell like glass containing lanthanide doped nanocrystals for efficient luminescence’ by Qunhuo Liu et al., Chem. Commun., 2018, 54, 13092–13095.

An effective and facile "on-off" fluorescence sensing approach for the determination of Fe

International audience; Transparent oxyfluoride glass and glass ceramics doped with 0.5% Ho3+ and 1.0% Yb3+ ions have been prepared. X-ray diffraction and transmission electron microscopy demonstrated the formation of NaYF4 nanocrystals during the heat treatment process. Raman spectra indicated the variation of glass structure brought about by the formation of NaYF4 nanocrystals. XRD curves and Judd-Ofelt intensity parameters confirmed the incorporation of Ho3+ into NaYF4 nanocrystals. Significantly enhanced visible upconversion and 2.85 mm emissions were achieved in glass ceramic under 980 nm laser diode pumping. A broadband spectrum with a full-width at half-maximum close to 132 nm was obtained in the glass ceramic. Besides, the calculated peak emission cross section was 0.6 x 10(-20) cm(2), suggesting that the glass ceramic is a promising gain material that can be applied to broadband amplifiers in the mid-infrared region. Furthermore, energy transfer mechanisms in glass and glass ceramics were proposed based on visible to mid-infrared emission spectra. It was found that the change in the photon energy environment around rare earth ions induced different dominant transitions in glass and glass ceramic. Finally, the influence of phonon energy on the transition processes was further quantitatively investigated, which may provide useful guidance for obtaining highly efficient 2.85 mm emission of holmium.

The spectral performance of the Tm3+/Er3+ co-doped tellurite glass under the pump at 808/980 nm and the energy transfer process between Tm3+ and Er3+ were mainly studied. The mid infrared fluorescence spectra showed that when the concentration of doped Er3+ ion was 0.5mol%, the fluorescence intensity of 1.8 μm and 2.7 μm reached the peak. While at the pump of 980 nm, the maximum occurred in 1mol% of Er3+ ions. Under 808/980 nm pumping system, different energy transfer mechanisms between Tm3+ and Er3+ ions were accordingly proposed. The maximum emission cross section of 0.5 Tm3+/0.5Er3+ codoped sample can reach 4.68 × 10−21 cm2 at 1886 nm. When P was 0.4, the gain of Tm3+:3F4→3H6 at 1852–2100 nm started to be positive while its maximum gain coefficient was 0.91 cm−1, and its central wavelength was 1887 nm. Therefore, the large emission cross section and the high gain are conducive to the Tm3+/Er3+ co-doped tellurite glass to obtain low threshold value and high gain of the 2 μm laser output.

Er/Ho co-doped oxyfluoride germanosilicate glass and glass ceramics are prepared and compared. The results indicate that the glass consists of SiO4 and GeO4 structural units, while the network of the glass ceramics consists of SiO4, GeO4, and GeO6 units together with NaYF4 nanocrystals. The presence of multiple local structures in glass ceramics creates a range of dipole environments, which is beneficial to the broadening of 2.7 μm emission. Two other reasons are attributed to the broadening of 2.7 μm emission in glass ceramics: the energy-level splitting of Er3+ and the enhancement of the Ho3+:I65→I75 transition in NaYF4 nanocrystals.