This paper presents four new temperature readout approaches to luminescence nanothermometry in spectral regions of biological transparency demonstrated on Yb3+/Er3+-doped yttrium aluminum garnet ...nanoparticles. Under the 10 638 cm−1 excitation, down-shifting near infrared emissions (>10 000 cm−1) are identified as those originating from Yb3+ ions' 2F5/2 → 2F7/2 (∼9709 cm−1) and Er3+ ions' 4I13/2 → 4I15/2 (∼6494 cm−1) electronic transitions and used for 4 conceptually different luminescence thermometry approaches. Observed variations in luminescence parameters with temperature offered an exceptional base for studying multiparametric temperature readouts. These include the temperature-dependence of: (i) intensity ratio between emissions from Stark components of Er3+ 4I13/2 level; (ii) intensity ratio between emissions of Yb3+ (2F5/2 → 2F7/2 transition) and Er3+ (4I13/2 → 4I15/2 transition); (iii) band shift and bandwidth and (iv) lifetime of the Yb3+ emission (2F5/2 → 2F7/2 transition) with maximal sensitivities of 1% K−1, 0.8% K−1, 0.09 cm−1 K−1, 0.46% K−1 and 0.86% K−1, respectively. The multimodal temperature readout provided by this material enables its application in different luminescence thermometry setups as well as improved the reliability of the temperature sensing by the cross-validation between measurements.
Eu3+-doped YxLu1−xNbO4 (x = 0, 0.25, 0.5, 0.75, 1) were prepared by the solid-state reaction method. YNbO4:Eu3+ and LuNbO4:Eu3+ crystallize as beta-Fergusonite (SG no. 15) in 1–10 μm diameter ...particles. Photoluminescence emission spectra show a slight linear variation of emission energies and intensities with the solid-solution composition in terms of Y/Lu content. The energy difference between Stark sublevels of 5D0→7F1 emission increases, while the asymmetry ratio decreases with the composition. From the dispersion relations of pure YNbO4 and LuNbO4, the refractive index values for each concentration and emission wavelength are estimated. The Ω2 Judd–Ofelt parameter shows a linear increase from 6.75 to 7.48 × 10−20 cm2 from x = 0 to 1, respectively, and Ω4 from 2.69 to 2.95 × 10−20 cm2. The lowest non-radiative deexcitation rate was observed with x = 1, and thus LuNbO4:Eu3+ is more efficient phosphor than YNbO4:Eu3+.
Nanoparticle‐mediated photothermal therapy (NP‐PTT) constitutes a flexible, highly selective, cost effective, and accurate tool for cancer treatment alone or in combination with other therapies such ...as radiotherapy or chemotherapy. The future application of NP‐PTT in real life mainly depends on the design and synthesis of novel multifunctional nanoparticles that could overcome the current limitations of NP‐PTT such as limited penetration depth and absence of therapy control. In this work, ultrasmall (≈2.4 nm) NdVO4 stoichiometric (100% constituent Nd3+ ions) nanoparticles are reported, which are capable of in vivo sub‐tissue localized heating under 808 nm optical excitation while providing, simultaneously, the possibility of high penetration near‐infrared fluorescence imaging. Ultrasmall stoichiometric NdVO4 nanoparticles have evidenced a superior light‐to‐heat conversion efficiency. This is explained in terms of their large absorption cross‐section at 808 nm (consequence of the particular spectroscopic properties of neodymium ions in NdVO4 and of the high neodymium content) as well as to their ultrasmall size that leads to large nonradiative decay rates. Results included in this work introduce ultrasmall, NdVO4 stoichiometric nanoparticles to the scientific community as multifunctional photothermal agents that could be considered as an alternative to traditional systems such as metallic, organic, or carbon‐based nanoparticles.
IR‐emitting NdVO4 ultrasmall nanoparticles show a remarkable photothermal conversion efficiency (72.1%) under 808 nm irradiation, which makes them particularly interesting for combined photothermal therapy and bioimaging. Their outsanding light‐to‐heat conversion capability, studied ex vivo and in vivo, would allow for photothermal treatments at laser intensities much lower than the ones used up to this moment with fluorescent rare earth‐based nanomaterials.
Gadolinium-oxide nanopowders doped with Yb3+ and Ho3+ ions and co-doped with alkali metal ions (Li+ and Na+) were synthesized via the polymer complex solution method and their up-conversion emission ...properties are analyzed. Prepared powders were well crystallized in cubic bixbyite structure, without any impurity phases and with an average crystallite size of about 25nm, as shown by X-ray powder diffraction analysis. No adsorbed species on the surface of nanoparticles were detected by infrared measurements. The particle morphology was analyzed by transmission electron microscopy, which revealed agglomerated crystalline nanoparticles with irregular, polygonal-like shapes, having a size in the range from 30 to 50nm. Up-conversion emission properties of Gd2O3:Ho3+,Yb3+ nanopowders were evaluated from photoluminescence emission and decay measurements using 980nm excitation. Two-photon up-conversion processes produced emissions in visible – near infrared spectral range, with the strongest green emission from 5F4,5S2→5I8 Ho3+ electronic transition, and weak red and near infrared from 5F5→5I8 and 5F4, 5S2→5I7 transitions, respectively. In addition, three-photon up-conversion emission was detected in ultra-violet–blue spectral region (5G4→5I8, 3D3→5I6 and 5G5→5I8 transitions). Luminescence measurements were performed on samples with different Ho3+ (0.5 and 1at%) and Yb3+ (2, 4 and 6at%) concentrations to find that 0.5at% of Ho3+ and 2at% of Yb3+ provides the most intense up-conversion emission. The influence of alkali metal (Li+ and Na+) ion co-doping is studied on the sample that showed the most intense up-conversion emission. Increase in the intensity of up-conversion emission is observed for both Li+ and Na+ co-doping. The effect is more pronounced with Li+, where addition of 5at% of Li+ led to more than one order of magnitude emission enhancement. Alkali metal ion co-doping also significantly improved up-conversion color purity through considerably larger increase of green emission compared to red and near infrared.
•Gd2O3:Yb3+, Ho3+ co-doped with alkali metal ions are prepared by the combustion method.•Optimal doping concentrations for UC is 0.5at% of Ho and 2at% of Yb.•Increase of UC emission intensity is observed for both Li+ and Na+ co-doping.•5at% of Li+ addition leads to more than one order of magnitude emission enhancement.•Alkali metal ions co-doping significantly improved up-conversion color purity.
The steady-state luminescence thermometry analysis was performed on thin-films of undoped Gd2O3 and Gd2O3 doped with Ho3+, Eu3+ and Er3+, created by the plasma electrolytic oxidation process. The ...experimental setup for luminescent measurements closely resembles the practical luminescent fiber-optic thermometer. The visible PL from Gd3+ was utilized for the luminescence intensity ratio method, exceling over the traditional method by using the thermally coupled levels, as it is superior by either better sensitivities, widened temperature range or improved temperature resolution. The relative uncertainty by our method is ~300 times lower @ 300 K for Gd2O3:Eu3+. The maximum relative sensitivities by the luminescence intensity ratio (LIR) of Gd2O3:Ho3+, Gd2O3:Eu3+ and Gd2O3:Er3+ are 0.12% @ 295 K, 0.44% @ 580 K and 1.1% @ 290 K, respectively. Line-shift showed a significant change solely for Eu3+ doped sample, by 0.076 cm−1 K−1. The full-width-half-maximum (FWHM) changes of undoped Gd2O3 and doped by Eu3+ at the high rate of 0.3 cm−1 K−1 @ 573 K and 0.53 cm−1 K−1 @ 300 K, respectively, but was marked impractical for other samples.
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Judd-Ofelt analysis has been performed from the photoluminescence emission spectra of Y2O3:Eu3+ with 3%, 1% and 0.1% doping concentration and YVO4:Eu3+ with 1% doping concentration, in temperature ...range from 40 °C to 460 °C. For precise calculation, an extended Sellmeier equation that accounts for the doping concentration and temperature dependence of the refractive index of Y2O3 doped with lanthanides is estimated. The temperature dependence of Ω2 and Ω4 parameters are fitted with quadratic and linear regression, respectively. Judd-Ofelt intensity parameters uniformly drop with increasing temperature, but at a different rate for different doping concentrations. From the Judd-Ofelt parameters radiative lifetimes and emission cross-sections were calculated. The cross-sections show a linear decrease with increasing temperature.
•Y2O3 doped with 3%, 1% and 0.1% and YVO4 doped with 1% Eu3+ concentration werecreated.•Photoluminescent spectra were recorded form 40 °C to 460 °C, with 20 °C steps.•Temperature, concentration and wavelength dependent Sellmeier equation is formed.•Ω2,4 parameters were fitted and temperature and concentration dependences established.•Stimulated emission cross-sections and lifetimes temperature dependence is presented.
Monoclinic scheelite-type BiVO4 is currently considered as one of the most promising non-titania photocatalysts, wheras tetragonal zircon-type BiVO4 is still poorly understood. Herein, a new and ...simple synthetic approach was applied and nanostructured single-phase zircon-type BiVO4 was successfully prepared by a controllable ethylene-glycol colloidal route. In addition, nanostructured monoclinic scheelite-type BiVO4 powders were also fabricated through annealing of the as-prepared samples. A comparative study of the two BiVO4 polymorphs was conducted and it turned out that the novel synthetic approach had a significant impact on porosity and photocatalytic performance of zircon-structured BiVO4. All the prepared materials, as-prepared and annealed, were mesoporous, while measured values of specific surface area of some zircon-structured samples (∼34 m2/g) were ∼7 times higher than those reported thus far for this phase. Interestingly, for the first time, zircon-type BiVO4, previously considered to be a poor photocatalyst, exhibited a better overall performance in degradation of methyl orange compared to monoclinic scheelite-type BiVO4. Hence, it could be expected that the here-presented synthesis and observations will both arouse interest in scarcely studied tetragonal zircon-type BiVO4 and facilitate as well as speed up further research of its properties.
Wooden cultural heritage serves as a very important source of information for historians and researchers. Also, it imposes an obligation on the science to keep this legacy for future generations in a ...proper condition. Among other techniques of conservation of wooden cultural heritage, a very suitable method is impregnation of the wood with the polymer, whereby the wood/polymer composites are formed. This paper describes the method of preparing the wood/polymer composites based on beechwood, using five different monomer systems. The method of lyophilization and subsequent polymerization by gamma radiation was used. After lyophilization and immersing in the monomer solutions, the wood samples were dried and irradiated with a dose of 25 kGy and different gamma irradiation dose rates. The weight of the samples before and after this procedure was measured. Also, changes in the mechanical properties of wood (compression test) before and after treatment were examined. We also examined the effect of radiation dose rate on polymerization. Based on the weight differences, dose rates and materials characterization we determined which of the monomer solution and dose rate are the most suitable for making beechwood/polymer composites.
•Wood/polymer composites have been prepared with different monomer compounds in order to improve the wood properties.•The method of lyophilization and subsequent polymerization by gamma radiation is used.•The monomer concentration and composition do not play a significant role in the amount of polymer loading.•Butyl methacrylate solutions show slightly higher loading values than styrene solutions.•The dose rate significantly affects the polymer loading - the values of polymer loading increase with the highest dose rate.
Temperature sensing from the photoluminescence of MgAl2O4:Cr3+ ceramic powder is systematically investigated. Material was prepared by self-propagating high temperature synthesis method. In this ...host, Cr3+ experiences the strong crystal field, so the overlapping emissions from 2E and 4T2 energy levels are observed. Emission and excitation spectra were recorded from 300 K to 540 K. The broad photoluminescence attributed to 4T2→4A2 emission gains in intensity with increase in temperature on account of 2E→4A2 emission intensity until 460 K when both emissions start quenching. The emissions were separated by deconvolution at each temperature and used for the luminescence intensity ratio temperature readout method. The obtained relative sensitivity exhibited high values in the physiological range, from 3.5 %K−1 at 300 K to 2.9 %K−1 at 330 K, above 2 %K−1 below 400 K and above 1 %K−1 between 400 K and 540 K.
Nowadays a large variety of applications are based on solid nanoparticles dispersed in liquids—so called nanofluids. The interaction between the fluid and the nanoparticles plays a decisive role in ...the physical properties of the nanofluid. A novel approach based on the nonradiative energy transfer between two small luminescent nanocrystals (GdVO4:Nd3+ and GdVO4:Yb3+) dispersed in water is used in this work to investigate how temperature affects both the processes of interaction between nanoparticles and the effect of the fluid on the nanoparticles. From a systematic analysis of the effect of temperature on the GdVO4:Nd3+ → GdVO4:Yb3+ interparticle energy transfer, it can be concluded that a dramatic increase in the energy transfer efficiency occurs for temperatures above 45 °C. This change is properly explained by taking into account a crossover existing in diverse water properties that occurs at about this temperature. The obtained results allow elucidation on the molecular arrangement of water molecules below and above this crossover temperature. In addition, it is observed that an energy transfer process is produced as a result of interparticle collisions that induce irreversible ion exchange between the interacting nanoparticles.
The interaction between nanoparticles and fluids has a major role in the properties of nanofluids. By means of nonradiative energy transfer between small luminescent nanoparticles dispersed in water, this work reveals how temperature affects the interactions between a liquid and particles. A crossover affecting diverse temperature‐dependent water properties is evidenced in the change of the luminescence of the nanoparticles.
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