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Radioluminescence and visible photoluminescence tunability features from a single Tm3+-doped yttrium tantalate phosphor prepared by a soft sol–gel method designed to afford cubic Y3TaO7 and monoclinic M′-YTaO4 crystalline phases are reported.

No abstract available. This work was supported by the Brazilian funding agencies Fapesp (grant number 2017/11301-2 and 2020/05319-9, and the scholarships processes numbers 2017/10424-3, 2018/04587-0, and 2020/00277-6), CNPq (grant number 303110/2019-8) and CAPES; the CICECO-Aveiro Institute of Materials project, UIDB/50011/2020 & UIDP/50011/2020, financed by national funds through the FCT/MEC and when appropriate co-financed by FEDER under the PT2020 Partnership Agreement; and by FCT (grant number SFRH/BD/139710/2018). published

This paper reports on the news about refractive index measurements and spectroscopic features of thin films, which can be applied as optical planar waveguides, focusing on their manufacturing processes, designs, and possible applications as optical amplifiers and sensors. Er3+-doped SiO2–Ta2O5 planar waveguides, with Si/Ta ratios of 90:10, 80:20, 70:30, 60:40, and 50:50, were prepared by a soft sol–gel process. Multilayer films were deposited by the dip-coating technique onto 10 μm SiO2–Si (100) p-type silicon and Si (100) silicon easily and successfully. The mechanisms of the densification process, porosity, and hydroxy group or water molecule occurrence have been accompanied by m-line and vibrational spectroscopy analyses. The thickness and refractive index values were used to understand better the influence of temperature and annealing time on the densification of the bulk films and the reduction of the pore volume as the tantalum oxide concentration increases. The refractive index shows the density of the films, and by the atomic force microscopy (AFM) technique, the films showed low surface roughness, achieving relatively high light confinement within the waveguide structure, and negligible optical loss due to surface scattering. Nanoparticle crystallization of Ta2O5 with size distribution ranging from 2.0 to 15.0 nm embedded in SiO2 was observed with size depending on annealing time and tantalum concentration. Intense and broadband emission positioned at 1550 nm, which is attributed to the 4I13/2 → 4I15/2 transition of Er3+ ions, was observed for all planar waveguides under excitation at 271, 272, and 278 nm. Depending on the porosity degree, the adsorption of H2O molecules occurs, changing the refractive index and contributing to the deactivation of excited states of Er3+ ions, making them an optical platform for use as an optical sensor for different species. Besides, the densified waveguides containing 20 or 30 mol % Ta exhibit high potential for applications as broadband optical amplifiers for wavelength division multiplexing (WDM), optical sensing, or augmented reality.

A thermometer based on single Nd3 + :Y2O3 nanoparticles is reported. The nanothermometer relies on the ratio of thermally coupled Nd3 + emission lines accessible by either continuous‐wave upconversion under 880 nm or downconversion under 532 nm excitation wavelengths. Both processes are modeled through rate equation systems based on multiphonon interactions between excited luminescent states, which led to excellent agreement with the experimental data. Moreover, the Y2O3 effective phonon mode energy was determined, showing the appropriateness of the theoretical approach used. The system presented a relative sensitivity up to 1.36% at 300 K while working within the first biological window, thus particularly useful for biological sensing applications.

This study investigates how rare earth ion (RE3+) concentration affects stabilization of the crystalline structure and infrared-to-visible upconversion (UC) in Er3+/Yb3+ co-doped yttrium tantalates, synthesized by the sol–gel method. Under 980 nm, the samples exhibited intense UC luminescence. The crystalline phases strongly influenced the emission color of UC luminescence. The sample consisting of pure Y3TaO7 phase had a yellowish-green color, but a greener emission appeared in the presence of a small amount of M’-YTaO4. Increasing the RE3+ concentration influences the Y3TaO7 crystalline phase stabilization, as well as in the color tunability, since cross-relaxation processes take place, enhancing red emission intensity. This is the first report of UC quantum yield (UCQY) for yttrium tantalate samples (up to 0.016 ± 0.002%). Samples doped with Er3+/Yb3+ 0.5/1.5 mol % annealed at 900 or 1100 °C were successfully developed as primary thermometers. The temperature of these materials can be predicted without any calibration through the Boltzmann law, using the ratio of the intensity of transitions of Er3+. The maximum relative thermal sensitivity was 1.31 ± 0.05% K−1, which was higher than the sensitivity reported for other oxides. Nanothermometer repeatability was 98.8% and 99.8%, with minimum temperature uncertainty of 0.93 and 0.87 K for samples annealed at 900 and 1100 °C, respectively. The great tunability properties, UCQY values, and nanothermometry results indicated that primary thermometers can be implemented by using Er3+/Yb3+ co-doped yttrium tantalate upconverting nanoparticles for biophotonic applications in temperature sensing and deep tissue imaging. published

Glass and glass-ceramics containing nanocrystals of Bi

Flexible coatings with dual capabilities for remote real-time temperature sensing and photothermal conversion have a huge potential in the field of advanced thermal actuated optoelectronic applicat...

We report the synthesis of a Y3TaO7 solid solution containing a high Eu3+ concentration (from 7 up to 50 mol%) and investigate how Eu3+ influences the Y3TaO7 crystallization process. To this end, we evaluate the Y3TaO7 structural features and photoluminescence properties after Eu3+ introduction into the Y3TaO7 lattice. The higher the Eu3+ ion concentration, the more stable the crystallization process of the Y3TaO7 phase seems to be. The Eu3+-containing Y3TaO7 displays intense orange-reddish, broad band emission because Eu3+ occupies different symmetry sites in the host and causes inhomogeneous broadening. Eu3+ emission quenching due to Eu3+ concentration is negligible up to 30 mol% and absolute quantum yield values of up to nearly 30% were obtained, making Eu3+-containing Y3TaO7 interesting materials for application as high-intensity emitters in photonics.

Er3+/Yb3+-Codoped tellurite glass-ceramics showed luminescence dependent on crystallization, promising to attend needs for the development of efficient photonic devices.

Highly intense NIR emissions in the first and second biological windows and a remarkable UV–Vis and NIR to NIR energy conversion were observed for Pr3+, Yb3+ co-doped yttria nanoparticles, synthesized via the homogeneous precipitation method. A single-phase body center cubic Y2O3 structure was formed for all the samples after annealing 900 °C for 2 h. Increasing the dopants content, from 0.5 to 5.0 mol %, the replacement of Y3+ by Pr3+ and Yb3+ ions lead to a lattice expansion, which could be calculated. Spherical monodispersed nanoparticles, constituted of several crystallites, were observed by TEM and SEM images. The particles size ranged from 143 to 272 nm for the as-prepared samples and from 88 to 202 nm for the samples annealed at 900 °C. The crystallite size was estimated by Debye-Scherrer and Williamson-Hall methods and ranged from 6 to 27 nm with an average of 13 nm. Photoluminescent studies evidenced pronounced Pr3+ and Yb3+ near infrared (NIR) emission under ultraviolet, visible, and NIR excitation. How the Yb3+ ions co-doping, as well as, the total rare earth content, affected the luminescence properties, were evaluated, along with the energy transfer process involving UV–Vis and NIR to NIR energy conversion between the doping ions and the host. The energy was transferred between the Y2O3 host and Pr3+, Yb3+ upon CT band excitation at 290 nm. NIR emission at 948, 1080, 1115 nm, and 1.5 μm attributed to the Pr3+ transitions 3P0,1→1G4, 1D2→3F3, 1D2→3F4, and 1D2→1G4, denoting the 1D2 population through a multiphonon relaxation process (3P0+3H4→3H6+1D2). A concentration quenching process was ascertained in the highest concentration of dopants (5.0 mol % in total), which indicated that cross-relaxation took place. Both the Yb3+-doped and Pr3+, Yb3+ co-doped samples presented the Yb3+ emission 2F5/2→2F7/2 at 976 nm. All the structural, morphological, and spectroscopic properties of the materials make these spherical yttria nanoparticles potential NIR emitting probes candidates for advances in biophotonics, especially for deep-tissue imaging using NIR I and NIR II biological windows.

Made available in DSpace on 2022-04-28T19:47:48Z (GMT). No. of bitstreams: 0 Previous issue date: 2021-12-01 Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) Fundação de Amparo à Pesquisa do Estado de Minas Gerais (FAPEMIG) Financiadora de Estudos e Projetos Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) Structural, optical and photoluminescent properties of Europium-doped potassium germanate glassy materials were investigated in terms of tantalum content and nanoscale crystallization of potassium tantalate K2Ta8O21. For such purpose, an Eu3+-doped germanate glass, Eu3+-doped tantalum germanate glass and Eu3+-doped tantalum germanate glass-ceramics were prepared and characterized by X-ray diffraction, Raman, UV–Vis–NIR and photoluminescence spectroscopies. Eu3+ emission properties were used as a sensitive probe to investigate its symmetry site into the host structure. The chemical microenvironment around Eu3+ ions have changed with tantalum concentration as well as bronze-like tantalum perovskite K2Ta8O21 phase crystallization into the glasses. The ions preferably occupy sites of higher symmetry and lower energy phonons, which attest the ions migration to the tantalum-rich crystalline environment. The correlation between the phonon side band (PSB) spectra and Raman vibrational modes, 5D0 → 7F2/5D0 → 7F1 ratio and experimental Eu3+ 5D0 lifetime support this assumption. The highest photoluminescence intrinsic quantum yield (QEuEu) is calculated for glass-ceramics heat-treated for 20 h by using Judd-Ofelt theory, indicating reduction of nonradiative decay processes due to the lower local phonon energy. The luminescence quenching for longer crystallization times demonstrates the importance of optimizing thermal treatment parameters to ensure proper distance between optically active ions. Accordingly, tantalum germanate glass-ceramics are promising for photonic devices as red laser, solid-state lighting and energy conversion applications, as well as for nonlinear optical applications considering the perovskite bronze-like crystallization. Grupo de Química de Materiais Universidade Federal de Alfenas Campus Poços de Caldas Instituto de Química Universidade Estadual Paulista - UNESP Departamento de Química Faculdade de Filosofia Ciências e Letras de Ribeirão Preto Universidade de São Paulo Instituto de Química Universidade Estadual Paulista - UNESP FAPESP: 2017/11301-2 FAPESP: 2020/01786-1 FAPESP: 2020/05319-9 CNPq: 303110/2019-8

Made available in DSpace on 2022-04-29T08:30:37Z (GMT). No. of bitstreams: 0 Previous issue date: 2021-07-01 In recent years, the use of quantum dots (Qdots) to obtain biological images has attracted attention due to their excellent luminescent properties and the possibility of their association with contrast agents for magnetic resonance imaging (MRI). In this study, Gd3+/ZnO (ZnOGd) were conjugated with Qdots composed of a gadolinium-copper-indium-sulphur core covered with a ZnS shell (GCIS/ZnS Qdots). This conjugation is an innovation that has not yet been described in the literature, and which aims to improve Qdot photoluminescent properties. Structural and morphological Qdots features were obtained by transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD) and thermogravimetric analyses (TGA). The photoluminescent properties were examined by emission (PL) and excitation (PLE) spectra. A new ZnOGd and GCIS/ZnS (ZnOGd-GCIS/ZnS) nanomaterial was synthesized with tunable optical properties depending on the ratio between the two native Qdots. A hydrophilic or lipophilic coating, using 3-glycidyloxypropyltrimethoxysilane (GPTMS) or hexadecyltrimethoxysilane (HTMS) on the surface of ZnOGd-GCIS/ZnS Qdots, was carried out before assessing their efficiency as magnetic resonance contrast agents. ZnOGd-GCIS/ZnS had excellent luminescence and MRI properties. The new Qdots developed ZnOGd-GCIS/ZnS, mostly constituted of ZnOGd (75%), which had less cytotoxicity when compared to ZnOGd, as well as greater cellular uptake. Department of Drugs and Medicines School of Pharmaceutical Sciences São Paulo State University (UNESP), Highway Araraquara-Jaú MINT INSERM CNRS SFR-ICAT UNIV Angers PRISM SFR-ICAT UNIV Angers Laboratório de Materiais Luminescentes Micro e Nanoestruturados—Mater Lumen Departamento de Química FFCLRP Universidade de São Paulo (USP) Department of Drugs and Medicines School of Pharmaceutical Sciences São Paulo State University (UNESP), Highway Araraquara-Jaú

Among several optical non-contact thermometry methods, luminescence thermometry is the most versatile approach. Lanthanide-based luminescence nanothermometers may exploit not only downshifting, but also upconversion (UC) mechanisms. UC-based nanothermometers are interesting for biological applications: they efficiently convert near-infrared radiation to visible light, allowing local temperatures to be determined through spectroscopic investigation. Here, we have synthesized highly crystalline Er3+, Yb3+ co-doped upconverting KGd3F10 nanoparticles (NPs) by the EDTA-assisted hydrothermal method. We characterized the structure and morphology of the obtained NPs by transmission electron microscopy, X-ray diffraction, Raman spectroscopy, and dynamic light scattering. Nonlinear spectroscopic studies with the Er3+, Yb3+: KGd3F10 powder showed intense green and red emissions under excitation at 980 and 1,550 nm. Two- and three-photon processes were attributed to the UC mechanisms under excitation at 980 and 1,550 nm. Strong NIR emission centered at 1,530 nm occurred under low 980-nm power densities. Single NPs presented strong green and red emissions under continuous wave excitation at 975.5 nm, so we evaluated their use as primary nanothermometers by employing the Luminescence Intensity Ratio technique. We determined the temperature felt by the dried NPs by integrating the intensity ratio between the thermally coupled 2H11/2→4I15/2 and 4S3/2→4I15/2 levels of Er3+ ions in the colloidal phase and at the single NP level. The best thermal sensitivity of a single Er3+, Yb3+: KGd3F10 NP was 1.17% at the single NP level for the dry state at 300 K, indicating potential application of this material as accurate nanothermometer in the thermal range of biological interest. To the best of our knowledge, this is the first promising thermometry based on single KGd3F10 particles, with potential use as biomarkers in the NIR-II region.

Er3+-doped and Er3+/Yb3+-codoped GeO2-Nb2O5-K2O glasses were prepared by conventional melt-quenching method. Thermal and spectroscopic analysis were performed. The niobium insertion into the glass structure has decreased the OH groups resulting in a slight increase in the luminescence efficiency as the niobium content. Glass network structure is modified depending on rare earth doping concentration and niobium content. The number of bridge oxygen bonds and nonbridge oxygen bonds is altered and consequently the crystallization composition. The spectroscopic features were discussed in terms of niobium concentration and its influence on the applications as optical devices. The addition of niobium broadens the emission band in the region of 1.5 µm covering C, S and L-telecommunication bands. The gain coefficient has calculated establishing high potentiality to use the niobium germanate glasses for optical amplification. The codoping by Er3+/Yb3+ intensifies the emission in the NIR and visible (upconversion) region in relation to the doped samples and may be interesting for application as visible and near-infrared emitters. In addition, the codoped samples with variable niobium contents have potential as visible tunable phosphors emitting either green or red light. Accordingly, the niobium germanate glasses are interesting matrices for rare earth ions doping and for the development of optical devices, such as visible and NIR laser and optical amplifiers.

Among several optical non-contact thermometry methods, luminescence thermometry is the most versatile approach. Lanthanide-based luminescence nanothermometers may exploit not only downshifting, but also upconversion (UC) mechanisms. UC-based nanothermometers are interesting for biological applications: they efficiently convert near-infrared radiation to visible light, allowing local temperatures to be determined through spectroscopic investigation. Here, we have synthesized highly crystalline Er3+, Yb3+ co-doped upconverting KGd3F10 nanoparticles (NPs) by the EDTA-assisted hydrothermal method. We characterized the structure and morphology of the obtained NPs by transmission electron microscopy, X-ray diffraction, Raman spectroscopy, and dynamic light scattering. Nonlinear spectroscopic studies with the Er3+, Yb3+: KGd3F10 powder showed intense green and red emissions under excitation at 980 and 1,550 nm. Two- and three-photon processes were attributed to the UC mechanisms under excitation at 980 and 1,550 nm. Strong NIR emission centered at 1,530 nm occurred under low 980-nm power densities. Single NPs presented strong green and red emissions under continuous wave excitation at 975.5 nm, so we evaluated their use as primary nanothermometers by employing the Luminescence Intensity Ratio technique. We determined the temperature felt by the dried NPs by integrating the intensity ratio between the thermally coupled 2H11/2→4I15/2 and 4S3/2→4I15/2 levels of Er3+ ions in the colloidal phase and at the single NP level. The best thermal sensitivity of a single Er3+, Yb3+: KGd3F10 NP was 1.17% at the single NP level for the dry state at 300 K, indicating potential application of this material as accurate nanothermometer in the thermal range of biological interest. To the best of our knowledge, this is the first promising thermometry based on single KGd3F10 particles, with potential use as biomarkers in the NIR-II region.

Most traditional photoactive materials for solar cell applications are sensitive to visible light, which highlights the importance of materials that are also active in the ultraviolet (UV) and infrared (IR) regions for an increase in energy conversion efficiency. SiO2-Gd2O3:Er3+/Yb3+/Eu3+ (xEr: 0.0–0.3; xYb: 0.0–1.2; xEu: 0.0–7.0 mol%) materials were prepared via sol-gel method, followed by thermal treatment at 900 °C for 8 h. The Gd2O3 crystalline cubic structure was determined by XRD and FT-IR, and the lattice parameters were investigated by Rietveld Refinement. Besides, the morphology was observed by SEM micrographs as a system in which Gd2O3 particles are dispersed in SiO2. In the EDX spectra. It was registered narrow bands arising from Er3+, Yb3+, and Eu3+ doping elements, besides Si4+, Gd3+, and O2-, confirming the presence of these elements in the composition. Under IR excitation at 980 nm, the samples showed upconversion phenomena, with Yb3+ ions working as sensitizers, and effective energy transfer between the doping RE3+ ions. The emission bands in the visible region are attributed to transitions of Er3+ ion, and Eu3+ ion transitions (enhanced up 66 times). Under UV excitation at 247.5 nm, it was observed the down shifting process, seen as narrow bands related to Eu3+ ion transitions. The samples showed red emission colors as the Eu3+ concentrations increased in the matrix for upconversion and down shifting process. The results suggest that xEu: 1.0 mol% is the optimal doping level of Eu3+ in the SiO2-Gd2O3 system. This triply doped sample was simultaneously excited at 980 nm and 247.5 nm. It was observed Eu3+ and Er3+ narrow bands in the visible region, responsible for both upconversion and down shifting process when doubly excited. For all these reasons, the materials are promising to be applied to the field of energy conversion and solar cell applications.

A dual tunable visible (reddish, orangish, blueish and white emission) and near infrared energy conversion in Pr3+-doped yttrium tantalate prepared by sol-gel method were observed depending on the ratio of radiative transitions from the 3P0 and 1D2 excited states. The Pr3+ concentration influences the crystallization process of cubic Y3TaO7 and monoclinic M’-YTaO4 crystalline phases as attested by X-ray diffraction and Raman spectroscopy. Increasing the lanthanide concentration, the Y3TaO7 crystalline phase is stabilized, delaying the formation of the M’-YTaO4 one. Spectroscopic studies revealed a pronounced near-infrared (NIR) emission of Pr3+ ions, ascribed to 1D2→3F3,4 transition, under ultraviolet (UV) and visible excitation. Changes in the emission profile were also noticed and could be correlated with the crystalline structure. A reduced multiphonon relaxation from the 3P0 to the 1D2 was observed due to the low phonon energy of the host. An intense blue emission (3P0→3H4) was detected, which is increased in comparison to the red emission, for higher dopant concentration. Samples containing the highest Pr3+ concentration (5.0 mol %) exhibited a luminescence quenching on the visible and NIR transitions from the 1D2 level indicating the influence of a cross-relaxation process on depopulating the 1D2 level and tuning the color emission. All the above-mentioned structural and luminescent properties make these yttrium tantalates potential candidates for Photonic applications, especially as red-orange-white-blue light emitters and as energy converters for the enhancement of commercial Si solar cell efficiency.

Ruthenium complexes containing catecholamines and catechol as ligands with general formula [Ru(NH3)4(catecholamine)]Cl, where “catecholamine” is isoproterenol (in complex 1), dopamine (in complex 2), noradrenaline (in complex 3), catechol (in complex 4), or adrenaline (in complex 5), were synthesized. The complexes were characterized by vibrational and NMR spectroscopies, mass spectrometry, cyclic voltammetry, and spectroeletrochemistry. The electronic and electrochemical features were analyzed in terms of the electronic density, which is affected by ruthenium complexation and different substituent groups on the aromatic ring. Resonance Raman spectra displayed bands assigned to the Ru(II)-semiquinone stretching frequencies, which agreed with the charge transfer band. Theoretical calculations helped to evaluate the metal-non-innocent ligand orbital mixing. All the results suggested that Ru(II)-semiquinone complexes are formed, and that the unpaired electron is delocalized between the metal ion and the non-innocent ligand.

Tellurite-zinc glasses doped with Er3+, Yb3+ and Tm3+ were fabricated by conventional melt-quenching technique and characterised by absorption spectroscopy, refractive index, lifetime measurements, excitation, luminescence and up-conversion spectroscopy. Tunable blue to cold white light emission based on the colour mixing of red, green and blue light was obtained via up-conversion under 980 nm and by adjusting the laser excitation intensity. The balancing of the relative intensity of each colour is provided by the energy transfer process between the rare-earth ions. Moreover, luminescence spectroscopy was performed with a 405 nm laser to further understand the energy transfer mechanism that produce the white light. The Judd-Ofelt intensity parameters ( Ω 2 , Ω 4 and Ω 6 ) were calculated for all samples and present the trend Ω 2 > Ω 4 > Ω 6 . The spectroscopic parameters were computed with the Judd-Ofelt theory as well as the energy transfer micro-parameters (critical radius of interaction and energy transfer coefficient). Such results shall be used to give a comprehensive explanation for the energy transfer process between these rare earth ions.

Color tunable blue-white-red emitting CaY0.99-xTb0.01EuxAlO4 phosphors were prepared by an easy and low-cost chemical route using citric acid as precursor. The structural and morphological properties were evaluated by XRD and SEM techniques. The photoluminescence spectra and decay curves under excitation at 352 nm reveals the energy transfer process from Tb3+ to Eu3+. The dependence of temperature on energy transfer was evaluated, indicating higher efficiency as the temperature increases The dominant mechanism was demonstrated to be dipole-dipole type. By adjusting the excitation wavelength, the color emission of CaYAlO4:Tb3+,Eu3+solids can be tuned from blue to red, through white light. The cell viability of this materials was performed in the saccharomyces cerevisiae medium culture observing the biocompatibility with 160 and 320 μg/mL of concentration. In parallel the white emission performance was analyzed by determining the CIE coordinates and color correlated temperature (CCT). The CaY0.985Tb0.01Eu0.005AlO4 material showed CIE coordinates (0.327, 0334) and CCT = 5755 K, making this material an example of single-phase white emitting system.

Luminescent spherical, redispersable, and monodisperse Er3+,Yb3+ co-doped Y2O3 nanoparticles were synthesized by homogenous precipitation followed by thermal annealing. Cubic Y2O3 nanoparticles exhibited high colloidal stability in water and biological medium and 90% cell viability toward glioblastoma multiforme cell lines. Confocal microscopy revealed cellular internalization of Y2O3 nanoparticles. Upon excitation at 980 nm, efficient near-infrared to visible upconversion luminescence from Y2O3:Er3+,Yb3+ nanoparticles occurred. The upconversion dynamics was determined by the number of photons, which evidenced that energy transfer by the upconversion mechanism is predominated. On the basis of luminescence nanothermometry studies, the nanoparticles exhibited features of a primary thermometer with high thermal sensitivity (1.27 ± 0.05% K−1 (303 K) and large repeatability (>97%), attesting that it can be used as a contactless optical thermal sensor. This primary thermometer is also successfully applied in a cell culture medium showing that the nanoparticles can operate on biological media. This opens the possibility of the use of Y2O3:Er3+,Yb3+ nanoparticles in the design of a theranostic platform, able to simultaneously monitor temperature and, coupled to photosensitizers, produce reactive oxygen species for cancer therapy.

This study reports the synthesis and the structural and spectroscopic characterization of Eu3+-doped yttrium tantalate prepared by a new sol–gel method, which affords the orthorhombic Y3TaO7 and monoclinic YTaO4. Eu3+ doping influences the crystallization kinetics; its presence delays YTaO4 formation. Spectroscopic studies and their correlation to the structural features were the basis to understand the high quantum efficiency and no evidence of concentration quenching and clustering formation of Eu3+ ions. Inhomogeneous broadening in the emission spectra is due to Eu3+ distribution in different Y3TaO7 symmetry sites. Higher YTaO4 content increases the ratio between the 5D0→7F2 and 5D0→7F1 transition intensities, suggesting that Eu3+ occupies relatively lower symmetry sites as compared to Eu3+ distribution in the Y3TaO7 phase. No quenching occurs even for samples containing the largest Eu3+ concentration (up to 5.0 mol%), which strongly indicates high Eu3+ solubility within the yttrium tantalate host and absence of Eu3+ clusters. In addition to its application as structural probe, high quantum efficiency values combined with enhanced emission intensity make Eu3+-doped yttrium tantalate a suitable red luminophore.

The rising demand for more efficient telecommunication networks that can carry larger data volume is currently one of the most pressing technological challenges. In this sense, developing new materials to obtain NIR broadband emission is an urgent matter. We have successfully prepared Tm3+/Yb3+ co-doped 70SiO2-30Nb2O5 and 70SiO2–30Ta2O5 (mol%) nanocomposites by the sol–gel method. The Tm3+/Yb3+ co-doped 70SiO2-30Nb2O5 and 70SiO2-30Ta2O5 nanocomposites displayed intense broad emission that extends from 1.6 to 2.1 µm, with maximum at 1.8 µm. The bandwidth values lied around 230 or 260 nm depending on the crystalline phase. Increasing rare earth content elicited discrete quenching, which attests to good rare earth solubility and distribution within the hosts. The luminescence results are outstanding in terms of silicate hosts and point to the potential application of these materials in optical amplifiers, remote sensing, and LIDAR systems.

We describe the synthesis of Pr3+/Yb3+ co-doped and Pr3+-doped SiO2-Nb2O5 nanocomposites; we also investigate energy transfer processes between the doping ions, which involve UV–Vis to infrared energy conversion. The emission spectra in the near infrared (NIR) region, 900–1650 nm, indicated energy transfer from Pr3+ to Yb3+ upon blue excitation of the Pr3+ ions. UV charge transfer band excitation elicited efficient Yb3+ emission at about 1.0 µm. The nanocomposite co-doped with 0.5 mol% Pr3+ and 1.0 mol% Yb3+ provided maximum energy transfer efficiency. The Pr3+ ion 3P0 excited state lifetime decreased from 11.8 to 3.7 µs as the Yb3+ ion content in the Yb3+/Pr3+ co-doped nanocomposites increased from 0.25 to 1.0 mol%. This observation attests for energy transfer from Pr3+ to Yb3+ ions. On the basis of these results, Pr3+/Yb3+ co-doped SiO2-Nb2O5 nanocomposites are promising materials for UV–Vis to NIR energy conversion.

This work reports on the preparation and photoluminescence properties of the phosphate glass matrix based on P2O5-Al2O5-Na2O-K2O (PANK) doped with Yb3+, Eu3+ and Er3+ with different amount of Nb2O5 prepared by the conventional melting process. The Raman bands assigned to the Nb2O5 indicating the insertion of this oxide in the glass. Under UV excitation, the emission spectra presented narrow bands assigned to the Eu3+, arising from the 5D0→7FJ (J = 0, 1, 2, 3 and 4). It was observed that the materials have at least two lifetimes values of the Eu3+ ion. In all materials, it was observed that the amount of Nb2O5 does not influence the photo-luminescent properties of the Eu3+ ion, providing potential applications in energy conversion. The optical properties like refractive index, optical basicity, optical electronegativity, Urbach Energy, direct and indirect band-gap, Judd-Ofelt parameters were calculated and the covalence bonding of Eu3+ with the neighbors ligands was evaluated as a function of Nb2O5 concentration. Co-doping with Er3+/Yb3+ promotes the emission in the infrared region, with a maximum around 1535 nm and bandwidth of 28 nm under 980 nm pumping.

High photoluminescence efficiency, unusual NIR broadband and tunable emission are possible in erbium-doped and tantalum germanate glasses and nanostructured glass-ceramics. The chemical microenvironment around erbium ions and their influence on optical properties are dependent on the TaO6 clusters formation and tantalum perovskite-like bronze crystallization, which are strongly related to the tantalum oxide content and annealing. Erbium ions are preferably distributed close to tantalum-rich environment, providing an intense emission with minimized nonradiative processes and inhomogeneous broadband NIR emission with increasing site numbers. A more pronounced broadening in the nanocrystalline samples is due to the multi-sites of the tantalum perovskite-like bronze crystalline structure. Green/red tunable emission from up conversion processes was observed since the erbium ions occupy a chemical environment with low phonon energy in the tantalum germanate glass and with close neighbors in the tantalum germanate glass-ceramics. Accordingly, the highly tantalum germanate glasses and glass ceramics are promising for photonic applications in optical amplification, lighting and lasing, as well as for nonlinear optical applications and studies considering the perovskite-like bronze crystalline samples.

We report on Nd3+-doped yttrium oxide polycrystalline nanoparticles synthesis, their basic structural characterization and the observation of phonon-assisted upconversion in single nanoparticles with different Nd3+ doping levels. For upconversion studies, a frequency-locked CW Ti: Sapphire laser operating @ 820 nm, resonant with a Stark level of the Nd3+ ions 4F5/2 manifold, was used to excite single nanoparticles on a home-made confocal microscope. To the best of our knowledge, luminescence ranging from 630 to 760 nm was observed for the first time from single Nd3+-doped yttria nanoparticles under such excitation conditions. Upconversion studies on different single nanoparticles revealed a good doping homogeneity and the upconversion emissions were found to be one-photon phonon-assisted processes.

Highly colloidal luminescent nanoparticles (NPs) 5 at% Er3+, 20 at% Yb3+:KY3F10 were prepared by EDTA assisted hydrothermal method. Spherical and monodispersed Er3+, Yb3+:KY3F10 nanoparticles with highly pure cubic phase exhibit attractive optical properties for their use in long-term biological studies because of the high chemical photo-stability and strong emissions in the visible and near infrared (NIR) regions. The luminescence spectra of Er3+, Yb3+:KY3F10 as dried powder and dispersed in physiologic medium show intense green upconversion emission transition in between 510 and 570 nm (2H11/2→4I15/2 and 4S3/2→4I15/2) and red upconversion emission transition in between 635 and 680 nm (4F9/2→4I15/2) under NIR light excitation (980 nm). The cellular nontoxicity of as-prepared Er3+, Yb3+ codoped KY3F10 to glioblastoma multiforme (GBM) cells, were reported for the first time to our knowledge. This nanomaterial shows potential use for theranostic applications in early detection of brain cancer, acting as biomarkers in the visible and NIR ranges, and as drug activators for some photobiological response as a coadjuvant therapy for cancer treatment, such as photodynamic therapy (PDT).

This study reports on how the niobium content influences the infrared-to-visible upconversion (UC) in Er 3+ /Yb 3+ co-doped SiO 2 -Nb 2 O 5 nanocomposites produced by an alternative sol-gel route. Raman spectroscopy, Transmission electron microscopy (TEM), and Photoluminescence spectroscopy (PL) helped to evaluate the structural and luminescent properties. The Nb 2 O 5 content impacted the nanocrystallization process—different Nb 2 O 5 polymorphs emerged, which affected the UC luminescence. An outstanding color tunability effect arose due to the unique structural features of the nanocomposites. Different green and red emissions appeared depending on the excitation power and on the Nb content. The Nb content of 30 mol% afforded luminescence of similar intensity in the green and red range. For higher than 40 mol% of Nb concentration, the luminescence was more intense in the red range. The green and red emissions indicated that an Energy Transfer Upconversion (ETU) process with Yb 3+ → Er 3+ energy transfer occurred efficiently. In addition, cross-relaxation process between Er 3+ ions is also accounted for the red emission.

Made available in DSpace on 2018-12-11T17:07:19Z (GMT). No. of bitstreams: 0 Previous issue date: 2016-12-01 Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) Fundação de Amparo à Pesquisa do Estado de Goiás Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) In this work, the structural and optical properties of the 60SiO2–20ZnO–20TiO2 system (in mol%) doped with 1 mol% of Eu3+ were evaluated. Stable and transparent sols, homogeneous gels, and powders were prepared by a soft chemical process followed by annealing from 700 to 1100 °C. Visible emission was observed in the photoluminescence (PL) spectra from 570 to 700 nm owing to the Eu3+ ions, with the most intense emission peaks at 614 and 590 nm related to the 5D0 → 7F2 and 5D0 → 7F1 transitions, corresponding to red (R) and orange (O) colors, respectively. The R/O intensity ratios between 3.16 and 3.73 were observed and correlated to the structural properties of the host. X-ray diffraction patterns indicated that the reduction of PL at 614 nm and changes in the R/O values were due to the crystallization process. In addition, the FTIR spectra showed a gradual decrease of the hydroxyl absorption bands around 3436 and 1640 cm−1 and an increase of the bands related to Ti–O–Ti and Si–O–Si linkages, indicating polymerization and densification process of the host was achieved above 700 °C. Moreover, increasing the annealing temperature resulted in the formation of ZnTiO3 and Zn2TiO4 crystalline phases, as well as rutile TiO2. Finally, intensity parameters (Ωλ), and quantum efficiency were calculated by applying Judd–Ofelt theory to Eu3+ ions, which showed that the Eu3+-doped samples can be used in displays and LEDs. Instituto de Química - UFG, Campus II, C.P. 131, CEP Instituto Federal de Educação Ciência e Tecnologia - Goiás, Parque Itatiaia, Campus Aparecida de Goiânia, CEP Departamento de Química Faculdade de Filosofia Ciências e Letras de Ribeirão Preto USP, Av. Bandeirantes, 3900, CEP Departamento de Química Geral e Inorgânica Instituto de Química UNESP, C.P. 355, CEP Instituto de Física - UFG, Campus II, C.P.131, CEP Departamento de Química Geral e Inorgânica Instituto de Química UNESP, C.P. 355, CEP

We have investigated how the Nb content influences the structural and luminescence properties of Er 3+ /Yb 3+ co-doped SiO 2 –Nb 2 O 5 nanocomposites prepared by an alternative sol-gel process at different Si/Nb molar ratios of 90:10 up to 20:80. X-ray diffraction (XRD), Transmission electron microscopy (TEM), Diffuse reflectance spectroscopy (DRS), Fourier transform infrared spectroscopy (FTIR), and Photoluminescence spectroscopy (PL) provided a detailed structural and spectroscopic analysis of the composites. Formation of the Nb 2 O 5 crystalline phases depended on the Si/Nb ratio. Nanocomposites with 20 up to 40 and 80 mol% of Nb contained the T crystalline phase, whereas nanocomposites with 50 mol% of Nb presented both the T and M crystalline phases. The average crystallite size increased from 5.9 nm to 33.8 nm as the niobium content, as revealed by XRD. The λ cutoff increased with the Nb content, and the band gap energy ranged from 4.27 eV to 3.54 eV. Full elimination of OH groups was suitable for the highest Nb concentrations, which influenced the luminescence properties. Efficient Yb 3+ → Er 3+ energy transfer occurred under 977-nm excitation, leading to broad and intense 1.5-µm emission for Nb30 and Nb40, with FWHM of 67 nm and 69 nm, respectively. Under 520-nm and host excitations, Er 3+ and Yb 3+ emissions at 1.0 µm took place. The different Nb 2 O 5 crystalline phases influenced the energy transfer processes between Er 3+ and Yb 3+ ions, which affected the relative intensity of the 1.0/1.5-μm emissions. Tuning of this relative intensity is possible depending on the Nb content, which paves the way for the application of these nanocomposites as optical amplifiers at 1.5 μm, solid-state lasers and energy converters. The Er 3+ /Yb 3+ co-doped nanocomposites with 30 and 40 mol% of Nb amount displayed the most promising luminescence properties for photonic applications.

This work describes the direct coupling of the in-tube solid-phase microextraction (in-tube SPME) technique to a tandem mass spectrometry system (MS/MS) to determine amino acids (AA) and neurotransmitters (NT) (alanine, serine, isoleucine, leucine, aspartic acid, glutamic acid, lysine, methionine, tyrosine, and tryptophan) in plasma samples from schizophrenic patients. An innovative organic-silica hybrid monolithic capillary with bifunctional groups (amino and cyano) was developed and evaluated as an extraction device for in-tube SPME. The morphological and structural aspects of the monolithic phase were evaluated by scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), nitrogen sorption experiments, X-ray diffraction (XRD) analyses, and adsorption experiments. In-tube SPME-MS/MS conditions were established to remove matrix, enrich analytes (monolithic capillary) and improve the sensitivity of the MS/MS system. The proposed method was linear from 45 to 360 ng mL&minus, 1 for alanine, from 15 to 300 ng mL&minus, 1 for leucine and isoleucine, from 12 to 102 ng mL&minus, 1 for methionine, from 10 to 102 ng mL&minus, 1 for tyrosine, from 9 to 96 ng mL&minus, 1 for tryptophan, from 12 to 210 ng mL&minus, 1 for serine, from 12 to 90 ng mL&minus, 1 for glutamic acid, from 12 to 102 ng mL&minus, 1 for lysine, and from 6 to 36 ng mL&minus, 1 for aspartic acid. The precision of intra-assays and inter-assays presented CV values ranged from 1.6% to 14.0%. The accuracy of intra-assays and inter-assays presented RSE values from &minus, 11.0% to 13.8%, with the exception of the lower limit of quantification (LLOQ) values. The in-tube SPME-MS/MS method was successfully applied to determine the target AA and NT in plasma samples from schizophrenic patients.

Eu3+-, Er3+-doped and Er3+/Yb3+-codoped niobium alkali germanate glasses, in the compositional host system GeO2-Nb2O5-K2O were synthesized by the conventional melt-quenching technique. Glass-ceramics were manufactured by controlled heat treatment of the precursor glasses. Homogeneous glasses and nanocrystalline glass-ceramics were investigated by DSC, XRD, TEM and spectroscopic analysis. K2Nb14O36 crystals are formed in the prepared glass-ceramics. This crystalline phase has low phonon energy as compared to the precursor glass and a variety of chemical sites for rare-earth ions. In glass-ceramics, the rare-earth ions occupy higher symmetry sites of the K2Nb14O36 nanocrystals resulting in inhomogeneous broadband emissions. Judd-Ofelt parameters were obtained for the Eu3+- and Er3+-doped samples. Glass-ceramics heat-treated for 20 h exhibited the highest photoluminescence quantum efficiency. The increased quantum efficiency is due to the decrease of nonradiative decay processes, that depopulate the excited levels, as well as the decrease in hydroxyl content and overall phonon energy. However, luminescence quenching is verified for samples with longer crystallization times, which emphasizes the importance of optimized heat treatment parameters. The gain coefficient and upconversion data were obtained and corroborate the potential application of these materials as photonic devices, such as visible and NIR laser and optical amplifiers.

A high intrinsic quantum yield and color purity red-emitting nanostructured Eu3+-doped 1-xSiO2-xNb2O5 materials were prepared by a new sol-gel route at different Si:Nb molar ratio for solid-state lighting and energy conversion. It was evaluated how the composition and annealing temperature can affect the structure of the materials and their luminescence features. Eu3+ ions distribution into the different symmetry sites of nanoscaled orthorhombic or monoclinic Nb2O5 particles considerately influenced their emission profile and efficiency. A UV and blue to red downshifting were detected, and by using Judd-Ofelt theory, high quantum intrinsic quantum yield up to 65% is calculated for the Eu3+ doped Nb2O5 nanoparticles upon excitation at 463 nm. Additionally, the chromaticity diagram figured out a red color purity up to 90.1% is obtained, making them promising material for solid-state lighting. The particle size and doping control make them possible to explore the solid-state property of nanoscaled Nb2O5 particles as a host, with the advantage of their homogenous dispersion in a silicate network, opening the possibility of their use as planar waveguides for solar cell concentrators and energy conversion for enhancement of solar cell efficiency.

This paper presents an evaluation of photoluminescent and structural properties of Eu 3+ -doped TiO 2 materials in powder form prepared by sol–gel process. The increase of heat-treatment temperature of synthesis results in the TiO 2 phase transition, obtaining anatase, rutile and sometimes brookite, examined by Raman and XRD techniques. Crystallite size as well as microstrains in the crystal structure were evaluated as a function of Eu 3+ and heat-treatment temperature. It was found that when Eu 3+ is introduced in anatase phase an intense color emission is observed under excitation at 394 and 463 nm. The rutile phase presents inversion center symmetry, and apparently the Eu 3+ tends to occupy this site, which decreases the intensity of the emission assigned to the 5 D 0 → 7 F 2 transition. The materials obtained at 700 °C showed most intensity of emission in the red region, verified by the ratio between 5 D 0 → 7 F 2 / 5 D 0 → 7 F 1 transitions of Eu 3+ . The results showed that the materials are interesting absorber in the ultraviolet and red region and can be used for improvement of energy conversion in solar cells devices.

A new sol–gel route was used for obtaining Er 3+ /Yb 3+ co-doped Nb 2 O 5 nanoparticles distributed in a SiO 2 based host. Phase separation and crystallization process were investigated for Er 3+ /Yb 3+ co-doped nanocomposites at 70Si:30Nb molar ratio. X-ray diffraction (XRD), Transmission Electron Microscopy (TEM), Fourier transform infrared (FTIR), Raman, and Photoluminescence (PL) spectroscopy were used to assess the structural properties and their influence on luminescence. Amorphous Nb 2 O 5 was identified after nanocomposite annealing at 700 °C, whereas at 900 °C and 1100 °C were identified both the orthorhombic and monoclinic phases. The average crystallite sizes were 6.6 nm at 900 °C and 16.4 nm at 1100 °C. Intense and broad NIR emission was observed for the nanocomposites annealed at 700 and 900 °C due to an efficient energy transfer from Yb 3+ to Er 3+ ions. Intense emissions at 980 nm and 1550 nm were also observed due to energy transfer from the host to Yb 3+ and Er 3+ ions, respectively. Additionally, a less efficient back energy transfer from Er 3+ to Yb 3+ ions was observed. The emission intensity and bandwidth were dependent on the nature of Nb 2 O 5 crystalline phase, indicating that rare-earth (RE) ions are mostly distributed into Nb 2 O 5 nanoparticles. The 4 I 13/2 and 2 F 5/2 excited state lifetimes were also dependent on Nb 2 O 5 crystalline phase with shorter values for monoclinic Nb 2 O 5 . The featured luminescent properties exhibited by the rare earth-doped Nb 2 O 5 make the nanocomposite materials potential candidates in many photonic applications.

Made available in DSpace on 2018-12-11T17:26:47Z (GMT). No. of bitstreams: 0 Previous issue date: 2016-02-01 This work reports on the Yb3+ ion addition effect on the near infrared emission and infrared-to-visible up conversion from planar waveguides based on Er3+-Yb3+ co-doped Nb2O5 nanocrystals embedded in SiO2-based nanocomposite prepared by a sol-gel process with controlled crystallization in situ. Planar waveguides and xerogels containing Si/Nb molar ratio of 90:10 up to 50:50 were prepared. Spherical-like orthorhombic or monoclinic Nb2O5 nanocrystals were grown in the amorphous SiO2-based host depending on the niobium content and annealing temperature, resulting in transparent glass ceramics. Crystallization process was intensely affected by rare earth content increase. Enhancement and broadening of the NIR emission has been achieved depending on the rare earth content, niobium content and annealing temperature. Effective Yb3+→Er3+ energy transfer and a high-intensity broad band emission in the near infrared region assigned to the Er3+ ions 4I13/2→4I15/2 transition, and longer 4I13/2 lifetimes were observed for samples containing orthorhombic Nb2O5 nanocrystals. Intense green and red emissions were registered for all Er3+-Yb3+ co-doped waveguides under 980 nm excitation, assigned to 2H11/2→4I15/2 (525 nm),4S3/2→4I15/2 (545nm) and 4F9/2→4I15/2 (670 nm) transitions, respectively. Different relative green and red intensities emissions were observed, depending upon niobium oxide content and the laser power. Upconversion dynamics were determined by the photons number, evidencing that ESA or ETU mechanisms are probably occurring. The 1931 CIE chromaticity diagrams indicated interesting color tunability based on the waveguides composition and pump power. The nanocomposite waveguides are promising materials for photonic applications as optical amplifiers and WDM devices operating in the S, C, and L telecommunication bands; and as upconverter materials for visible upconversion lasers, biomedical applications, energy conversion for solar cells and others. Departamento de Química Faculdade de Filosofia Ciências e Letras de Ribeirão Preto Universidade de São Paulo, Av. Bandeirantes, 3900 Grupo de Pesquisa em Química de Materiais - (GPQM) Departamento de Ciências Naturais Universidade Federal de São João Del Rei Campus Dom Bosco, Praça Dom Helvécio, 74 Grupo Física de Materiais Instituto de Física Universidade Federal de Goiás Campus II, C.P. 131 Institute of Chemistry- São Paulo State University- UNESP PSL Research University Chimie ParisTech - CNRS Institut de Recherche de Chimie Paris Sorbonne Universités UPMC Univ Paris 06 Institute of Chemistry- São Paulo State University- UNESP

In this work a procedure to determine the local structure of the optically active site was developed. The local structure of the Eu3+ ion in high symmetry sites of the SnO2 ( D 2 h ) and BaLiF3 ( D 4 d ) crystals was carried out using the simple overlap model (SOM) and the method of equivalent nearest neighbours (MENN). From equations of the crystal field parameters (CFP), of the maximum splitting of F 1 7 multiplet and of the electrostatic equilibrium of luminescent site it was possible to predict the Eu-NN distances. The overlap between the 4f and 2p orbitals has been 0.05 and the charge factor between 0.45 ≤ g j ≤ 8.0 . The Batista–Longo Improved Model (BLIM) was used to show that the Eu3+ ion charge can be greater than its own valence. The F 1 7 level splitting (316 cm−1 for the SnO2; and 83 cm−1 for the BaLiF3) and the predicted Stark levels are in very good agreement with the experimental data. In all cases the magnitude of the charge factors are quite close to each other. This strongly indicates that the Eu3+ ion treats any chemical species in its immediate neighbourhood as negative charges.