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In 2016, the China Meteorological Administration organized the “Megacity Experiment on integrated Meteorological Observation in China” to realize the continuous quantitative observation of aerosol profiles in megacities by using aerosol lidar. In order to ensure the quantitative comparability of the observed data of aerosol lidar, in September 2017, the CMA Meteorological Observation Centre carried out the first megacity experiment in the South suburb Observatory of Beijing. In the calibration test of aerosol lidar, the hardware system calibration of six lidars and the calibration of 2km-5km are completed by using the method of statistical analysis. This is the second aerosol calibration test of the Megacity Experiment in 2018. For the first time, the standard aerosol lidar developed by the University of Naples in Europe is introduced as the standard source, and 10 lidars from different manufacturers participating in the joint test are calibrated and compared at the same site at the same time. The results show that: REAL LIDAR as a reference source is equivalent to the calibration results using statistical methods. In the future, REAL LIDAR can be used as a standard to calibrate other lidar by means of quantum transfer. In this paper, the system deviation and standard deviation of backscatter coefficient of 1-8 km are obtained, and the results meet the calibration requirements of European EARLINET. This work promotes the improvement of the data quality of aerosol lidar, ensures the reliability and consistency of the data when multiple lidar network observation, and provides the basis for lidar to enter the real-time business NET.

Pr3+/Er3+ co-doped tellurite glass with composition 80TeO2-10Na2O-5WO3-5Nb2O5 was synthesized by the conventional melt-quenching technique, and the obtained glass was characterized by the UV/Vis/NIR absorption spectrum, near-infrared fluorescence spectrum, differential scanning calorimeter (DSC) curve, X-Ray diffraction (XRD) pattern and Raman spectrum. Under the 488 nm excitation, it was found that Pr3+/Er3+ co-doped tellurite glass could emit an ultra-broadband near-infrared fluorescence which extended from 1200 to 1650 nm with full-width at half-maximum (FWHM) of about 236 nm, and this ultra-broadband fluorescence was contributed by the multichannel emissions of Pr3+ and 1.53 µm band emission of Er3+. The luminescent mechanism and energy transfer processes between Pr3+ and Er3+ ions which are responsible for the observed ultra-broadband fluorescence were analyzed. Meanwhile, optical absorption bands that are assigned with corresponding electronic transitions with respect to Pr3+ and Er3+ ions were identified from the measured absorption spectrum, and based on the optical absorption data, the gain coefficient and important spectroscopic parameters like Judd-Ofelt intensity parameter, spontaneous radiative transition probability, radiative lifetime and branching ratio were calculated to elucidate the radiative properties of doped rare-earth ions. In addition, the DSC curve exhibited the good thermal stability of glass host with Δ T >150 °C, Raman spectral study displayed the presence of different vibrational groups and XRD pattern confirmed the amorphous structural nature of the prepared glass. The present results indicate that Pr3+/Er3+ co-doped tellurite glass is promising for the ultra-broadband near-infrared band fiber amplifiers covering the expanded low-loss communication window.

Improving the lasing emission property of rare-earth doped vitreous material is a research topic. In this paper, Er3+/Yb3+/Tm3+ tri-doped tellurite glasses with and without WO3 component were synthesized using melt-quenching technique and the effect of WO3 addition on the 1.80 μm band fluorescence of Tm3+ was investigated. The obtained samples were characterized by X-ray diffraction (XRD) pattern, differential scanning calorimeter (DSC) curve, Raman spectrum, UV/Vis/NIR absorption spectrum, near-infrared emission spectrum and fluorescence decay curve. The XRD pattern confirmed amorphous structural nature of synthesized tellurite glass, the DSC curve revealed good thermal stability with Δ T >100 °C and the Raman spectrum displayed a stretching vibration band around 920 cm−1 for glass host with WO3. Under the excitation of 980 nm laser diode (LD), the intense 1.80 μm band fluorescence of Tm3+ originated from the 3F4→3H6 transition was observed in the Er3+/Yb3+/Tm3+ tri-doped tellurite glass and the intensity increases further with the addition of a certain amount of WO3, which is attributed to the enhanced energy transfers from Yb3+ (Er3+) to Tm3+ ions due to the increased phonon energy of glass host. The energy transfer mechanism between them was elucidated by analyzing fluorescence decay behavior of Tm3+ and quantitatively calculating energy transfer coefficient as well as phonon contribution ratio. Meanwhile, based on the absorption spectrum, some important spectroscopic parameters such as Judd-Ofelt parameter, spontaneous radiative transition probability, fluorescence branching ratio, absorption and emission cross-sections, and gain coefficient spectrum were calculated to reveal spectroscopic properties of doped Tm3+ ions. The obtained results indicate that Er3+/Yb3+/Tm3+ tri-doped tellurite glass with an appropriate amount of WO3 is a promising gain medium applied for the 1.80 μm band solid-state lasers.

In this work, the near-infrared photoluminescence properties in Tm3 +/Ho3 + co-doped tellurite glass was investigated. The tellurite glass with composition TeO2-ZnO-Na2O-La2O3 was synthesized using conventional melt-quenching technique and characterized by UV/Vis/NIR absorption and near-infrared emission spectroscopies, fluorescence decay measurement and differential scanning calorimeter (DSC) analysis. Under the excitation of 808 nm laser diode (LD), a broadband 2.0 μm band luminescence ranging from 1600 to 2200 nm with a full width at half maximum (FWHM) of 362 nm was observed, which was contributed by 1.85 μm fluorescence from Tm3 +: 3F4 → 3H6 and 2.05 μm fluorescence from Ho3 +: 5I7 → 5I8. The fluorescence emission of Ho3 + was originated from the energy transfer from Tm3 + to Ho3 + ions, and the energy transfer mechanism was elucidated by analyzing fluorescence decay behavior of Tm3 + and quantitative calculation of phonon contribution joined in the energy transfer process. Meanwhile, based on the absorption spectrum, some important spectroscopic parameters such as Judd-Ofelt intensity parameter, spontaneous radiative transition probability, fluorescence branching ratio, absorption and emission cross-sections, and gain coefficient spectrum were calculated to reveal the spectroscopic properties of doped tellurite glass. Furthermore, from the DSC curve it can be derived that the investigated glass possesses a good thermal stability with ΔT(= Tx − Tg) larger than 152 °C. These results indicate that Tm3 +/Ho3 + co-doped tellurite glass could be a promising gain medium applied for 2.0 μm near-infrared band broad fiber amplifiers and tunable fiber lasers.

Pr3+-doped tellurite glasses containing metallic silver NPs were synthesized by the conventional melt-quenching technique. Structural, thermal and optical properties of the synthesized glass samples were characterized by X-Ray diffraction (XRD) curves, Raman spectra, differential scanning calorimeter (DSC) curves, transmission electron microscopy (TEM) images, UV/Vis/NIR absorption and near-infrared fluorescence emission spectra. The XRD curves confirmed the amorphous structural nature of the synthesized glasses, the Raman spectra identified the presence of different vibrational groups, the DSC curves verified the good thermal stability, and the TEM images revealed the nucleated silver NPs with average diameter about 10 nm dispersed in the glass matrix and its surface Plasmon resonance (SPR) absorption band was located at around 510 nm. Besides, Judd-Ofelt intensity parameters Ω t (t = 2, 4, 6) and other important spectroscopic parameters like transition probability, radiative lifetime, branching ratio were calculated to evaluate the radiative properties of Pr3+ levels from the measured optical absorption spectra. It was found that Pr3+-doped tellurite glasses could emit an ultra-broadband fluorescence extending from 1250 to 1650 nm under the 488 nm excitation, and this fluorescence emission increased further with the introduction of silver NPs. The enhanced fluorescence was mainly attributed to the increased local electric field around Pr3+ induced by silver NPs. The present results demonstrate that Pr3+-Ag codoped tellurite glass is a promising candidate for the near-infrared band ultra-broadband fiber amplifiers covering the expanded low-loss communication window.

This paper reports an enhanced and broadband near-infrared fluorescence emission in the Pr3+/Nd3+ co-doped tellurite glass, which was prepared using melt-quenching technique. Under the excitation of 488 nm laser diode (LD), three near-infrared emission bands at around 0.9, 1.04 and 1.30 μm from 3P1,0 → 1G4, 1G4→3H4 and 1G4→3H5 radiative transitions respectively were observed in the Pr3+ single-doped glass, and the fluorescence intensities increased further with the introduction of Nd3+ ions, which is mainly attributed to the energy transfers from Nd3+ to Pr3+ emissions. Meanwhile, the spectral overlapping of Pr3+:1G4→3H4 and Nd3+:4F3/2 → 4I11/2 radiative transitions resulted in a broadband emission ranging from 1000 to 1100 nm, whose full-width at half-maximum (FWHM) reached about 66 nm. Additionally, the spectroscopic properties of Nd3+ and Pr3+ ions were analyzed using Judd-Ofelt theory and the thermal stability property of prepared glass was characterized by the differential scanning calorimeter (DSC) measurement, and larger than 134 °C for the difference Δ T ( = T x − T g ) was observed, which indicates its feasibility for later fiber drawing. The enhanced fluorescence and broadband emission indicate that Pr3+/Nd3+ co-doped tellurite glass can be applied in the near-infrared band tunable lasers and broadband optical amplifiers.

The B 2 O 3 oxide in different concentration was introduced into Er 3+ /Ho 3+ codoped tellurite glass with conventional composition TeO 2 ZnO Na 2 O to investigate its effect on the near-infrared band luminescence of doped rare-earth ions under the excitation of 980 nm LD. The UV/Vis/NIR absorption spectrum, Vis/NIR fluorescence emission spectrum, fluorescence decay curve, DSC curve and Raman spectrum of the prepared glass samples were measured and investigated. With the introduction of B 2 O 3 in a certain concentration range, the 1.55 μm band fluorescence of Er 3+ improved greatly, whereas the 2.03 μm band one of Ho 3+ decreased first and then increased slightly. The Judd-Ofelt intensity parameter, radiative transition probability, quantum efficiency, multi-phonon relaxation rate and energy transfer micro-parameter were calculated to explain the obtained experimental results. The present works indicate that the enhanced multi-phonon relaxation of excited state ions and energy transfer between Er 3+ and Ho 3+ ions due to the increased phonon energy of glass host with the introduction of B 2 O 3 are responsible for the observed luminescent phenomena, and Er 3+ /Ho 3+ codoped tellurite glass with an appropriate amount of high phonon energy B 2 O 3 is a promising candidate applied for the near-infrared band solid-state lasers and fiber amplifiers.

Tellurite glasses with different concentrations of Nd3 + ions and WO3 oxide were prepared using melt-quenching technique. The prepared glasses were characterized by the absorption spectrum, emission spectrum, Raman spectrum, fluorescence decay curve and DSC curve measurements, together with Judd-Ofelt intensity parameter, radiative transition probability and fluorescence branching ratio calculations to reveal the effects of Nd3 + and WO3 concentration on the structure, photo-luminescence and thermal stability. Under the excitation of 808 nm LD, three near-infrared band fluorescence emissions at around 0.9, 1.06 and 1.34 μm, corresponding to the transitions from the 4F3/2 → 4I9/2, 4I11/2 and 4I13/2 levels respectively, are observed, and the fluorescence intensities increase with the increase of doped Nd3 + concentration up to 0.6 mol%. Furthermore, the fluorescence intensities continue to increase greatly with the introduction of WO3 oxide. Compared with 0.6 mol% Nd3 +-doped glass without WO3 oxide, the luminescent intensity of 1.06 μm band increases by about 95% in the glass with 9 mol% amount of WO3, which is mainly attributed to the rapid population of Nd3 + ions in the excited level 4F3/2 due to the enhanced multi-phonon relaxation process with the increased phonon energy of glass host. Therefore, the enhanced luminescent intensity as well as the good thermal stability demonstrated by DSC curve indicate that the prepared 0.6 mol% Nd3 +-doped tellurite glass with 9 mol% amount of WO3 oxide is a potential gain medium applied for near-infrared band solid-state lasers and fiber amplifiers.

Metallic silver nanoparticles (Ag NPs) with various concentrations were embedded into Er3+/Tm3+/Yb3+ tri-doped tellurite glasses prepared using melt-quenching and heat-treated techniques. Heat-treatment at temperature above the glass transition temperature induced the nucleation and growth of near-spherical shape silver NPs confirmed by the transmission electron microscopy (TEM) images, and the average diameter of silver NPs was about 10 nm. The thermal stability, structural and optical properties of the prepared glasses were characterized by the differential scanning calorimeter (DSC) curves, X-ray diffraction (XRD) patterns, absorption spectra, luminescence spectra and fluorescence decay curves. The DSC curves displayed that the prepared glasses possess good thermal stability with ∆ T larger than 138 °C while the XRD patterns indicated the amorphous structural nature. Under the excitation of 980 nm LD, the luminescence spectra exhibited two intense near-infrared band fluorescence at 1.81 and 1.53 μm in the wavelength range of 1400–2200 nm, which are originated from the Tm3+:3F4 → 3H6 and Er3+:4I13/2 → 4I15/2 transitions respectively. With the embedding of 0.5 mol % amount of silver NPs, the 1.81 μm band fluorescence of Tm3+ increased significantly by about 70%, mainly due to the local electric field enhanced effect induced by silver NPs on the basis of energy transfers from Er3+ to Tm3+ ions, and the energy transfer efficiency, micro-coefficient and critical radius were calculated to elucidate the interaction mechanism between Er3+ and Tm3+ ions. Additionally, the intensity parameters Ω t (t = 2, 4, 6) and radiative properties of Tm3+ such as the transition probabilities, radiative lifetimes and branching ratios were calculated from the measured absorption spectra based on Judd-Ofelt theory. The present results indicate that the Er3+/Tm3+/Yb3+ tri-doped tellurite glass with an appropriate amount of silver NPs is a promising luminescent material applied for the near-infrared band solid-state lasers and fiber amplifiers.

WO3 oxides with relatively high phonon energy and different concentrations were introduced into the Nd3+-doped tellurite-based glasses of TeO2-ZnO-Na2O to improve the 1.32 μm band fluorescence emission. The absorption spectra, Raman spectra, 1.32 μm band fluorescence spectra and differential scanning calorimeter (DSC) curves were measured, together with the Judd-Ofelt intensity parameters, stimulated emission and gain parameters were calculated to evaluate the effects of WO3 amount on the glass structure and spectroscopic properties of 1.32 μm band fluorescence. It is shown that the introduction of an appropriate amount of WO3 oxide can effectively improve the 1.32 μm band fluorescence intensity through the enhanced multi-phonon relaxation (MPR) processes between the excited levels of Nd3+. The results indicate that the prepared Nd3+-doped tellurite glass with an appropriate amount of WO3 oxide is a potential gain medium applied for the O-band broad and high-gain fiber amplifier.

The Er 3+ /Tm 3+ co-doped tellurite glasses with and without silver nanoparticles (Ag NPs) have been synthesized by the conventional melt-quenching technique and characterized by the UV/Vis/NIR absorption spectra, 1.85 μm band fluorescence emission spectra, differential scanning calorimeter (DSC) curves, X-ray diffraction (XRD) curves and transmission electron microscopy (TEM) images to investigate the effects of Ag NPs on the 1.85 μm band spectroscopic properties of Tm 3+ ions, thermal stability and structural nature of glass hosts. The TEM image reveals the presence of Ag NPs with average diameter of ∼14 nm in the prepared Er 3+ /Tm 3+ co-doped tellurite glasses, and the presence of Ag NPs significantly enhance the 1.85 μm band fluorescence emission of Tm 3+ ions under the excitation of 808 nm LD, which is mainly attributed to the intensified local electric field induced by Ag NPs scattered around the doped rare-earth ions, together with the energy transfer between Er 3+ and Tm 3+ ions. The energy transfer mechanisms between Er 3+ and Tm 3+ ions were further investigated by calculating energy transfer micro-parameters and phonon contribution ratios. Meanwhile, the Judd-Ofelt intensity parameters Ω t ( t = 2,4,6), spontaneous radiative transition probabilities, fluorescence branching ratios and radiative lifetimes of relevant excited levels of Tm 3+ ions were calculated based on the Judd-Ofelt theory to reveal the improved effects of Ag NPs on the 1.85 μm band spectroscopic properties. An improvement by about 75% of fluorescence intensity is found in the studied Er 3+ /Tm 3+ co-doped tellurite glass containing 1.0 mol% amount of Ag NPs, and the thermal stability of glass host increases slightly with the Ag NPs while the glass structure maintains the amorphous nature. The above results indicate that the prepared Er 3+ /Tm 3+ co-doped tellurite glass with an appropriate amount of Ag NPs is a promising host material applied for 1.85 μm band solid-state lasers and amplifiers.

Tm3+/Yb3+ co-doped tellurite glasses with different silver nanoparticles (Ag NPs) concentrations were prepared using the conventional melt-quenching technique and characterized by the UV/Vis/NIR absorption spectra, 1.85 μm band fluorescence emission spectra, transmission electron microscopy (TEM) images, differential scanning calorimeter (DSC) curves and X-ray diffraction (XRD) patterns to investigate the effects of Ag NPs on the 1.85 μm band spectroscopic properties of Tm3+ ions, thermal stability and structural nature of glass hosts. Under the excitation of 980 nm laser diode (LD), the 1.85 μm band fluorescence emission of Tm3+ ions enhances significantly in the presence of Ag NPs with average diameter of ∼8 nm and local surface Plasmon resonance (LSPR) band of ∼590 nm, which is mainly attributed to the increased local electric field induced by Ag NPs at the proximity of doped rare-earth ions on the basis of energy transfer from Yb3+ to Tm3+ ions. An improvement by about 110% of fluorescence intensity is observed in the Tm3+/Yb3+ co-doped tellurite glass containing 0.5 mol% amount of AgNO3 while the prepared glass samples possess good thermal stability and amorphous structural nature. Meanwhile, the Judd-Ofelt intensity parameters Ω t (t = 2,4,6), spontaneous radiative transition probabilities, fluorescence branching ratios and radiative lifetimes of relevant excited levels of Tm3+ ions were determined based on the Judd-Ofelt theory to reveal the enhanced effects of Ag NPs on the 1.85 μm band spectroscopic properties, and the energy transfer micro-parameters and phonon contribution ratios were calculated based on the non-resonant energy transfer theory to elucidate the energy transfer mechanism between Yb3+ and Tm3+ ions. The present results indicate that the prepared Tm3+/Yb3+ co-doped tellurite glass with an appropriate amount of Ag NPs is a promising lasing media applied for 1.85 μm band solid-state lasers and amplifiers.

For enhancing the 2.0 μm band fluorescence of Ho3+, a certain amount of WO3 oxide was introduced into Ho3+/Tm3+/Yb3+ tri-doped tellurite glass prepared using melt-quenching technique. The prepared tri-doped tellurite glass was characterized by the absorption spectra, fluorescence emission and Raman scattering spectra, together with the stimulated absorption, emission cross-sections and gain coefficient. The research results show that the introduction of WO3 oxide can further improve the 2.0 μm band fluorescence emission through the enhanced phonon-assisted energy transfers between Ho3+/Tm3+/Yb3+ ions under the excitation of 980 nm laser diode (LD). Meanwhile, the maximum gain coefficient of Ho3+ at 2.0 μm band reaches about 2.36 cm-1. An intense 2.0 μm fluorescence emission can be realized.

Improving the spectroscopic properties of rare earth (RE) doped glass materials is a challenging task. In the present work the metallic silver nanoparticles (Ag NPs) were embedded into Er 3+ /Yb 3+ codoped tellurite glasses with composition TeO 2 –Bi 2 O 3 –TiO 2 , prepared using melt-quenching and subsequent heat-treated techniques, and the improved effect of Ag NPs on the 1.53 μm band fluorescence of Er 3+ ions was investigated. About 24 h heat-treatment of Er 3+ /Yb 3+ codoped tellurite glass containing 1 mol % amount of AgNO 3 at the temperature 370 °C yielded the well-dispersed and near-spherical Ag NPs with ∼11.4 nm average diameter as evidenced by transmission electron microscopy (TEM) image. The intense 1.53 μm band fluorescence was observed in the prepared Er 3+ /Yb 3+ codoped tellurite glasses under the excitation of 980 nm and was further improved with the presence of Ag NPs in the glass matrix, which is attributed to the enhanced local electric field around doped RE ions induced by Ag NPs and the possible energy transfer from Ag NPs to Er 3+ ions. The enhanced local electric field was well demonstrated by comparing the variation of emission spectra of hypersensitive probe Eu 3+ ions in tellurite glasses with and without Ag NPs. From the Judd-Ofelt analysis, it was also found that the value of Ω 6 intensity parameter increased slightly with the increase of Ag NPs concentration in a certain range, also confirming the possibility of realizing strong fluorescence emission. In addition, the amorphous structural nature was demonstrated by the measured X-ray diffraction (XRD) patterns with no sharp diffraction peak. The enhanced 1.53 μm band fluorescence indicates that the Er 3+ /Yb 3+ codoped tellurite glass with an appropriate amount of Ag NPs is a promising candidate for the development of Er 3+ -doped fiber amplifiers (EDFAs) applied in the WDM systems.

In this work, trimesic acid was introduced in the preparation of cerium-manganese oxide, and its effect on thermal aging resistibility for catalytic diesel soot elimination was investigated systematically. The prepared catalysts were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), N2 adsorption–desorption, X-ray diffraction (XRD), Raman spectra, X-ray photoelectron spectroscopy (XPS) and H2-temperature programmed reduction (H2-TPR). The experimental results show that trimesic acid addition has no significant effect on the morphologies of cerium-manganese oxide catalyst, and also contribute litter to the suppression of catalyst particles sintering and textual features destroying. In addition, the crystal structure and high-temperature (800 °C) phase separation of CeO2-MnOx solid solution are not improved by the trimesic acid modification. But, noteworthily, trimesic acid assisted synthesis can obviously promote Mn4+ generation and keep up oxygen vacancy concentration and hence improve the product of highly active oxygen species (especially O 2 - ) of CeO2-MnOx catalyst during the thermal aging process. Furthermore, trimesic acid assistance can significantly alleviate the loss of CeO2-MnOx metal-support interaction caused by thermal aging, and maintain the ability to supply active oxygen at low-temperature (approximately 200–400 °C). Finally, after thermal aging at 800 °C for 12 h, the trimesic acid assisted synthesized CeO2-MnOx catalyst shows significantly better catalytic soot oxidation activity. Thus this work reveals that besides stabilizing textual and structural properties, stabilizing and optimizing electronic structure is another feasible pathway to enhance the thermal aging resistibility of CeO2-based soot oxidation catalysts.