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[en] This paper reports the microwave hydrothermal synthesis and infrared to visible upconversion luminescence of Er3+/Yb3+ co-doped Bi2MoO6 nanopowder. Crystal structure, morphology and chemical composition were analyzed by means of X-ray Diffraction, Transmission Electron Microscopy and Raman Spectroscopy. Upconversion luminescence properties were studied in detail. The infrared to visible upconversion luminescence has been investigated in Er3+/Yb3+ doped Bi2MoO6 with different Yb3+ concentrations. Intense green and red upconversion emissions around 532, 545, and 655 nm corresponding to the 2H11/2, 4S3/2, and 4F9/2 transitions, respectively, to the 4I15/2 ground state were observed when excited by CW laser radiation at 980 nm. The effect of Yb3+ on the upconversion luminescence intensity was analyzed and the upconversion luminescence mechanism was explained in terms of the energy transfer process. From this study, it confirms that the like fluorides, and germinate glasses, metal oxide nanoparticles could also be a potential host to achieve desired upconversion luminescence. -- Highlights: • Er3+/Yb3+ co-doped bismuth molybdate nanopowder was successfully synthesized. • Infrared to visible upconversion luminescence was observed at 980 nm excitation. • Green and red emissions at 532 nm, 546 nm and 656 nm were investigated. • Bismuth molybdate could be a potential host material for upconversion luminescence
[en] Mesoporous spherical Yb–Er-doped nanoparticles were prepared by sol–gel method. The structure and morphology of the nanoparticles were characterized using Raman, Fourier transform infrared spectroscopies, transmission electron microscopy and by low-temperature adsorption. It is shown that both anatase (tetragonal) and brookite (orthorhombical) phases are present in the titania nanoparticles. Their diameter size is between 12 and 15 nm and an average surface area of 136 . Under infrared irradiation, the nanoparticles show luminescence by an upconversion process of the ytterbium and erbium ions, the green emission corresponds to transition and for the red emission, the transition energy is: –. The green and red photoluminescence intensities are highly dependent on the OH amount, which is produced during the hydrolysis and condensation processes and depends on the reaction time, nanoparticles wash and annealing temperature. The influence of synthesis parameters on the properties of porosity and luminescence was studied by the Plackett–Burman experimental design.
[en] In this work, poly(methyl methacrylate) (PMMA) thin films and a polymer optical fiber doped with pyrromethene (PM-567) were fabricated and characterized. The obtained films were uniform and homogeneous in its central zone and no aggregation of dye molecules were observed. UV–vis absorption, photoluminescence spectra, lifetime and photodegradation were measured for the fabricated films. Peak intensity and position of the photoluminescence spectra were dependent on the pyrromethene concentration. A resonant energy transfer mechanism is proposed as the main process associated with this behavior. Photodegradation results were well fitted by a gamma probability density function. While thin films were highly degraded under 405 nm excitation, the studied optical fiber displayed a much more stable behavior, presumably related with its construction design based on a transparent core and a thin PM-567 doped cladding.
[en] In this paper, we report the microwave hydrothermal synthesis of Er3+/Yb3+ co-doped Bi2MoO6 upconversion photocatalyst. Crystal structure, morphology, elemental composition, optical properties and BET surface area were analyzed in detail. Infrared to visible upconversion luminescence at 532 nm and 546 nm of the co-doped samples was investigated under excitation at 980 nm. The results revealed that the co-doping of Er3+/Yb3+ into Bi2MoO6 exhibited enhanced photocatalytic activity for the decomposition of rhodamine B under simulated solar light irradiation. Enhanced photocatalytic activity can be attributed to the energy transfer between Er3+/Yb3+ and Bi2MoO6 via infrared to visible upconversion from Er3+/Yb3+ ion and higher surface area of the Bi2MoO6 nanosheets. Therefore, this synthetic approach may exhibit a better alternative to fabricate upconversion photocatalyst for integral solar light absorption. - Graphical abstract: Schematic illustration of the upconversion photocatalysis. Display Omitted - Highlights: • Er3+/Yb3+ co-doped Bi2MoO6 upconversion photocatalyst is successfully synthesized. • We obtained the nanosheets having high surface area. • Upconversion of IR to visible light was confirmed. • Upconversion phenomena can be utilized for effective photocatalysis
[en] In this paper we report the infrared to visible upconversion luminescence properties of Er"3"+/Yb"3"+ co-doped BaMoO_4 nanocrystals synthesized via microwave assisted sol–gel processing route. Structural, morphological and upconversion luminescence properties were investigated by X-ray diffraction (XRD), Transmission Electron Microscopy (TEM), UV–vis diffuse reflectance spectroscopy (UV–vis DRS) and Upconversion Photoluminescence spectra analysis. Results revealed that the oval shaped BaMoO_4 nanocrystals ranging in size from 40 to 60 nm having tetragonal scheelite crystal structure were obtained by sol–gel route. The infrared to visible upconversion luminescence has been investigated in Er"3"+/Yb"3"+ co-doped in BaMoO_4with different Yb"3"+ concentrations. Intense green upconversion emissions around 528, 550 nm, and red emission at 657 nm corresponding to the "2H_1_1_/_2, "4S_3_/_2, and "4F_9_/_2 transitions, respectively to the "4I_1_5_/_2 ground state were observed when excited by CW laser radiation at 980 nm. The green emissions were greatly enhanced after the addition of sensitizer (Yb"3"+ ions). The effect of Yb"3"+ on the upconversion luminescence intensity was analyzed and explained in terms of the energy transfer process based. The reported work establishes the understanding of molybdates as an alternative host material for upconversion luminescence. - Graphical abstract: Infrared to visible upconversion luminescence of Er"3"+/Yb"3"+ co-doped BaMoO_4 nanocrystals. - Highlights: • Nanocrystals were synthesized by microwave assisted sol–gel processing route. • Strong green emissions were observed in Er"3"+/Yb"3"+ co-doped BaMoO_4 nanocrystals. • Provides an insight on Upconversion luminescence properties of oxides host materials
[en] The tellurite fibers based on glasses with the composition TeO2–WO3–Nb2O5–Na2O–Al2O3–Er2O3–Yb2O3 were fabricated by the rod-in-tube technique using a Heathway drawing tower. The upconversion luminescence of Er3+/Yb3+ codoped tellurite glass fibers under 980 nm excitation were investigated. The Er3+/Yb3+co-doped tellurite fibers show an efficient up-conversion process in comparison with the Er3+-doped tellurite fibers. The pump power dependent intensities were discussed, which showed that two photons are involved in the upconversion process. - Highlights: ► We fabricate Er3+/Yb3+ codoped TeO2–WO3–Na2O–Nb2O5–Al2O3 glass fibers. ► We evaluate the upconversion luminescence of these tellurite fibers. ► The pump power dependent intensities were discussed. ► The Er3+/Yb3++co-doped tellurite fibers show an efficient upconversion process. ► We show that two photons are involved in the upconversion process.
[en] Spectroscopic characterization of Er"3"+/Yb"3"+ co-doped tellurite glasses 70.8TeO_2–5Al_2O_3–13K_2O–(11−x)–BaO–0.2Er_2O_3–xYb_2O_3, where x=0, 0.4, 0.8, 1.2 and 2 mol% has been carried out through X-ray diffraction, Raman, absorption and luminescence spectra. The Judd–Ofelt intensity parameters were calculated for 0.2 mol% Er"3"+-doped glass and are used to evaluate radiative properties such as transition probabilities, branching ratios and radiative lifetime. The emission cross-section of the "4I_1_3_/_2→"4I_1_5_/_2 transition has been calculated from the absorption data using McCumber's theory. The emission intensity of both, visible and infrared signals as a function of Yb_2O_3, have been studied under 980 nm and 375 nm laser excitation. The physical mechanisms responsible for both, visible and infrared signals in the tellurite samples have been explained in terms of the energy transfer and excited state absorption process. The FWHM of the "4I_1_3_/_2→"4I_1_5_/_2 transition as a function of Yb_2O_3 mol% and distance (δ) between the laser focusing point and the end-face of the glass has been reported. It was observed both, experimentally and numerically, a change in the FWHM with variations of δ less than 8 mm. The latter was attributed to the radiation trapping effect. - Highlights: • Er"3"+/Yb"3"+ co-doped tellurite glasses were fabricated by the melt-quenching technique. • The structural, thermal and optical properties of the tellurite glasses were studied. • The radiation trapping effect has been observed in small tellurite glass samples. • Tellurite glasses could be a potential material for fiber fabrication
[en] Both preform and polymer optical fiber with a Poly(methyl methacrylate) core and THV–Rhodamine 6G cladding were characterized. UV–vis absorbance, photoluminescence spectra and lifetime of the preform were measured. Axial and lateral photoluminescence spectra of the polymer optical fiber were studied under 404 nm excitation in order to study the illumination performance of the fiber. It was observed that the peak wavelength from the fiber photoluminescence spectra is higher than the peak wavelength from the fiber preform and that the peak wavelength from the fiber photoluminescence spectra is red shifted with the fiber length in the case of axial emission. The obtained results suggest the influence of self-absorption on the photoluminescence shape. Strong lateral emission along the fiber was observed with the naked eyes in all the cases. The lateral photoluminescence spectra show that the lateral emission is a combination between the pump laser and the Rh6G molecule photoluminescence. The results suggest that this polymer optical fiber could be a potential candidate for the development of fiber lighting systems. - Highlights: • Axial and lateral emission along the fiber was studied. • Self-absorption effect was confirmed in the case of axial photoluminescence. • The lateral emission is a combination between the laser and the RhG6 emission. • This fiber could be a potential candidate for the development of lighting systems.
[en] In this work, the photodegradation of a polymer optical fiber with Rhodamine doped cladding as a function of illumination time and excitation intensity is presented. To show the effect of photodegradation on different bulk geometries and environments, the photodegradation from a dye doped preform and a PMMA thick film is also evaluated. The reversible and the irreversible degradation of the florescent material were quantified under an established excitation scheme. To this purpose, a four-level system to model the photodegradation rates and its relation with the population of the states is presented and it is used to justify a possible underlying mechanism. The obtained results suggest an increase of one order of magnitude in the stability (lifetime) of the polymer optical fiber with respect to the preform or the thick film geometry stability.
[en] Fluorophosphate glasses of composition (P_2O_5–K_2O–Al_2O_3–CaO–CaF_2)-doped with various Nd_2O_3 concentrations were prepared by a melt quenching technique and their thermal, vibrational and optical properties were investigated. Thermal stability of the fluorophosphate glass has been determined from differential scanning calorimetric thermograph. The vibrational modes of the present glass have been studied using Raman spectrum. The intensity parameters, Ω_λ (λ=2, 4 and 6) as well as radiative properties for the "4F_3_/_2 level of Nd"3"+ ion, have been evaluated from the absorption spectra of 1.0 mol% Nd_2O_3-doped glass using the Judd–Ofelt theory. Strong near infrared emission at 1.06 =m attributed to "4F_3_/_2→"4I_1_1_/_2 transition has been obtained for all the glasses upon 806 nm diode laser excitation. Decay analysis has been carried out and found that the lifetime for the "4F_3_/_2 level of Nd"3"+ ion was found to be higher compared to the other Nd"3"+-doped glass host matrices. The quantum efficiency and saturation intensity have been determined to be 93% and 2.32×10"8 W/m"2, respectively for 1.0 mol% Nd_2O_3-doped glass. The results indicate that the present glasses could be useful for 1.06 µm laser applications. - Highlights: • Nd"3"+-doped K–Al–Ca fluorophosphate glasses were prepared and characterized. • Raman and DSC measurements have been carried out. • Strong near infrared emission at 1.06 μm ("4F_3_/_2→"4I_1_1_/_2 transition) has been found. • Optical properties have been evaluated and compared to other host matrices. • Higher lifetime and quantum efficiency have been noticed in the studied glasses