This paper presents the Cr3+-activated Mg2TiO4 phosphor temperature dependance of its near infrared luminescence and its potential in the optical thermometry applications. In this respect, ...temperature dependences of three emission features were tested over the broad temperature range (10–500 K): (i) the luminescence intensity ratio (LIR) between emissions from 4T2→4A2 and 2E→4A2 transitions, (ii) the emission lifetime, and (iii) the shift of the 2E→4A2 emission band. We observed that LIR follows the Boltzmann equation for T > 300 K with the maximal value of relative sensitivity of 1.73 %K−1. The lifetime value of the 2E→4A2 transition strongly decreases with temperature with a maximal relative sensitivity of about 0.75 %K−1 at around 430K. Finally, the shift of the emission band is about 65 cm−1 over the complete temperature range.
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•Synthesis of single phase Mg2TiO4:Cr3+ phosphor.•Multi readout approach to temperature sensing in first biological NIR window.•The maximum relative sensitivity of 1.73 %K−1 in the LIR mode at physiological temperatures.•The maximum relative sensitivity 0.75 %K−1 in the lifetime mode in broad temperature range from 100 K to 400 K.•Significant red shift of the Cr3+ R line with temperature increase.
The introduction of additional functionalities to materials is exceptionally important as it opens new applications for them. Aluminum, one of the most abundant and important materials, is coated ...with luminescent Sm2+‐doped γ‐aluminium oxide to impart thermometric functionality. Considering the potential industrial applications, two of the most widely used aluminum alloys, 6061 and 7075, are also coated. For this purpose, plasma electrolytic oxidation (PEO), an effective technique for producing hard ceramic coatings on various metal surfaces, is used. It is shown that thermometric coatings can be produced on aluminum in one‐step process by adding the raw precursor to the electrolyte. The valence reduction of Ln3+ to Ln2+ is achieved during the PEO process. The intense and broad (orange to deep red) emission from the coating shows supersensitivity to temperature changes over the 100–648 K range. The temperature is obtained from the coating emission using i) the emission intensity ratio method, ii) emission lifetime, and iii) emission band position with sensitivities of 4.8% K−1, 1.2% K−1, and 8 cm−1 K−1, respectively. Several applications would benefit from the thermometric coating's excellent temperature resolution of 0.04 K and the choice of three temperature read‐outs that facilitate the coating's use in different luminescence thermometry setups.
Aluminum is coated with the luminescent Sm2+‐doped γ‐Al2O3, thus having embedded thermometric functionality. Intense, broad orange–deep red emission shows the supersensitivity to temperature changes over 100–648 K. Temperature is retrieved from the emission using: i) intensity ratio; ii) lifetime, and iii) band position method with sensitivities of 4.8% K−1; 1.2% K−1 and 8 cm−1 K−1, respectively.
Luminescence with temperature changes in its intensity, energy, spectral shape, peak width in the steady-state, or lifetime and phase shift in the impulse regime. Those most often undesired effects ...(but endorsed for the luminescence thermometry) have been modeled depending on the material type and physical phenomena involved, resulting in numerous equations and explanations. However, there is not a single publication that collected all of the theories and guided the reader to their proper application. Here we devised a review of all prominent theoretical models, for all types of materials and all temperature-induced phenomena on luminescence, extended the original research, and provided the advanced, yet user-friendly, multiplatform, software for fitting the experimental data. The software can be obtained from https://www.omasgroup.org/lumthools/for free. As it is interactive, it is also capable of demonstrating the effect of each fitting parameter on the change of the fitting curve, it calculates and graphs the figures of merit in luminescence thermometry, and exports the data in a format ready for publication.
•Temperature causes changes in all spectral features of all phosphors.•>30 theoretical models are given and compared for these phenomena.•Paper aids in selecting a proper model for a given phosphor.•Luminescence thermometry models and methods are included in the review.•Free, OpenSource, interactive software for fitting of experimental data is presented.
This paper demonstrates the effects of Li+ co-doping on the structure, morphology, and luminescence properties of GdVO4:Er3+/Yb3+ phosphor prepared using a high-temperature solid-state chemistry ...method. The GdVO4:Er3+/Yb3+ powders synthesized with the Li+ co-dopant (in concentrations of 0, 5, 10, and 15mol%) are characterized by X-ray powder diffraction, scanning electron microscopy, and photoluminescence spectroscopy. Structural analysis showed that powders co-doped with Li+ have larger crystallite sizes and slightly smaller crystal lattice parameters than powders prepared without Li+ ions. Photoluminescence down-conversion (345-nm excitation) and up-conversion (980-nm excitation) spectra show characteristic Er3+ emissions, with the most intense bands peaking at 525nm (2H11/2→4I15/2 transition) and 552nm (4S3/2→4I15/2). The intensity of up-conversion emission from GdVO4:Er3+/Yb3+ is enhanced (by a factor of four) by co-doping with 5mol% of Li+ ions. The mechanisms responsible for this emission enhancement are discussed.
UC emission spectra for GdVO4:1.5-mol% Er3+/20-mol% Yb3+ powders co-doped with different concentrations of Li+ ions, recorded under 980-nm excitation. Display omitted
•5-mol% Li+ co-doped powders have 400% enhanced up-conversion emission intensity.•15-mol% Li+ co-doping produces 40% higher emission in down-conversion.•Li+ co-doped powders have larger crystallite size and smaller lattice parameters.
This paper provides the detailed study of (nano)particle's size effect on structural and luminescent properties of LaPO4:Eu3+ synthesized by four different methods: high temperature solid-state, ...co-precipitation, reverse micelle and colloidal. These methods delivered monoclinic monazite-phase submicron particles (> 100nm), 4 × 20nm nanorods and 5nm spheres (depending on the annealing temperature), 2 × 15nm nanorods, and ultra-small spheres (2nm), respectively. The analysis of emission intensity dependence on Eu3+ concentration showed that quenching concentration increases with a decrease of the particle size. The critical distance for energy transfer between Eu3+ ions is found to be 18.2Å, and the dipole-dipole interaction is the dominant mechanism responsible for the concentration quenching of emission. With the increase in Eu3+ concentration, the unit-cell parameter slightly increases to accommodate larger Eu3+ ions at sites of smaller La3+ ions. Photoluminescent emission spectra presented four characteristic bands in the red spectral region: at 592nm (5D0→7F1), at 612nm (5D0→7F2), at 652nm (5D0→7F3) and at 684nm (5D0→7F4), while in small colloidal nanoparticles additional emission bands from host defects appear at shorter wavelengths. Intensities of f-f electronic transitions change with particles size due to small changes in symmetry around europium sites, while emission bandwidths increase with the reduction of particle size due to increased structural disorder. Judd-Ofelt analysis showed that internal quantum yield of Eu3+ emission is strongly influenced by particle's morphology.
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•Pechini-type synthesis provide rare earth-doped Gd2Ti2O7 nanoparticles of about 20 to 50nm.•The energy levels of the Sm3+ and Eu3+ ions in Gd2Ti2O7 are evaluated.•The strongest emissions are found ...for Gd2Ti2O7 containing 2.5at.% of Sm3+ and 15at.% Eu3+.•Long emission decays of 5.9ms for Eu3+ and 5ms for Sm3+ in Gd2Ti2O7 are recorded.
This work describes the synthesis and photoluminescent properties of rare earth (Sm3+ and Eu3+) doped Gd2Ti2O7 pyrochlore nanopowders. Pure-phase rare earth-doped Gd2Ti2O7 nanoparticles of approximately 20–50nm in diameter, as evidenced from X-ray diffraction and electron microscopy analysis, are produced via the mixed metal–citric acid complex method. A temperature of 880°C is identified for the formation of the crystalline pyrochlore phase, based on a differential thermal analysis of Gd2Ti2O7 precursor gels. From photoluminescence excitation and emission spectra, measured at 10K and room temperature, the energy levels of Sm3+ and Eu3+ ions in Gd2Ti2O7 nanoparticles are obtained. The dependence of luminescence emission intensity and emission decays on rare earth concentration are measured and discussed. The strongest Sm3+ orange–reddish emission is observed for samples containing 2.5at.% of Sm3+ ions, while in the case of Eu3+, the most intense emission is found for 15at.% Eu3+ doping. The 4G5/2 level lifetime decreases with an increase in Sm3+ concentration, from about 5ms (for 0.1–0.2at.% of Sm3+) to 2.4ms (for 2.5at.% of Sm3+). With an increase in Eu3+ concentration in the Gd2Ti2O7 nanoparticles, the Eu3+5D0 level lifetime decreases from ∼5.9ms (for 0.5at.% of Sm3+) to 3.1ms (for 15at.% of Sm3+).
Na/K-ATPase is emerging as an important target for a variety of anticancer metal-based drugs. The interactions of Na/K-ATPase (in its E1 state) with three representative and structurally related ...cytotoxic gold(iii) complexes, i.e. Au(bipy)(OH)
PF
, bipy = 2,2'-bipyridine; Au(py
-H)(CH
COO)
, py
-H = deprotonated 6-(1,1-dimethylbenzyl)-pyridine and Au(bipy
-H)(OH)PF
, bipy
-H = deprotonated 6-(1,1-dimethylbenzyl)-2,2'-bipyridine, are investigated here in depth using a variety of spectroscopic methods, in combination with docking studies. Detailed information is gained on the conformational and structural changes experienced by the enzyme upon binding of these gold(iii) complexes. The quenching constants of intrinsic enzyme fluorescence, the fraction of Trp residues accessible to gold(iii) complexes and the reaction stoichiometries were determined in various cases. Specific hypotheses are made concerning the binding mode of these gold(iii) complexes to the enzyme and the likely binding sites. Differences in their binding behaviour toward Na/K-ATPase are explained on the ground of their distinctive structural features. The present results offer further support to the view that Na/K-ATPase may be a relevant biomolecular target for cytotoxic gold(iii) compounds of medicinal interest and may thus be involved in their overall mode of action.
•Luminescent thermometer based on SrTiO3:Mn4+ nanocrystals has been synthesized.•The multimodal temperature readout using this luminescent thermometer was presented.•The readout multimodality ...enhances the reliability of the temperature sensing.•Obtained S are one of the highest already reported for thermometers based on Mn4+.
The constant striving to improve the quality of thermal imaging with the use of luminescent thermometers imposes the search for new materials with better and better thermometric properties. The facility in the modulation of the spectroscopic properties of transition metal doped materials makes them particularly attractive for this type of application. Therefore, in response to this expectation, in this manuscript we report the novel SrTiO3:Mn4+ nanocrystals as a thermographic phosphor of extraordinary thermometric properties in the biologically relevant temperatures. The high relative sensitivity of the SrTiO3:Mn4+ nanocrystals to temperature changes in each of the three temperature readout modes presented in this manuscript, namely 8.67%/K at 313 K in the intensity mode, 3.5%/K at 348 K in the lifetime mode and 5.64%/K at 303 K in the ratiometric mode, make this material one of the most promising candidates for highly sensitive temperature imaging.
The surface modification of nanocrystalline TiO2 particles (45 Å) with salicylate-type ligands consisting of an extended aromatic ring system, specifically 3-hydroxy-2-naphthoic acid, ...3,5-dihydroxy-2-naphthoic acid and 3,7-dihydroxy-2-naphthoic acid, was found to alter the optical properties of nanoparticles in a similar way to salicylic acid. The formation of the inner-sphere charge-transfer (CT) complexes results in a red shift of the semiconductor absorption compared to unmodified nanocrystallites and a reduction in the band gap upon the increase in the electron delocalization when including an additional ring. The investigated ligands have the optimal geometry for binding to surface Ti atoms, resulting in ring coordination complexes of a salicylate-type (binuclear bidentate binding-bridging) thus restoring the six-coordinated octahedral geometry of surface Ti atoms. From both absorption measurements in methanol/water = 90/10 solutions and steady-state quenching measurements of modifier fluorescence upon binding to TiO2 in aqueous solutions, stability constants in the order of 10(3) M(-1) have been determined at pH 2 and pH 3. Fluorescence lifetime measurements, in the presence and absence of colloidal TiO2 nanoparticles, indicated that the fluorescence quenching process is primarily static quenching, thus proving the formation of a nonfluorescent CT complex. The binding structures were investigated by using FTIR spectroscopy. Quantum chemical calculations on model systems using density functional theory (DFT) were performed to obtain the vibrational frequencies of charge transfer complexes, and the calculated values were then compared with the experimental data.
Upconversion sub-micron particles are one of the most perspective materials due to their wide application range, the most important being in the bio-medicinal field where they can be used for ...labeling, sensing, treatment or drug delivery. Chemically stable upconversion sub-micron particles of La2O2S co-doped with Yb3+/Ho3+ and Yb3+/Tm3+ were synthesized and characterized. Different concentrations of Yb3+/Ho3+ and Yb3+/Tm3+ were successfully incorporated into the hexagonal crystal structure of lanthanum oxysulfide using the optimized solution combustion synthesis method with urea as a fuel. Sub-micron particles of less than 50 nm in diameter showed the typical upconversion photoluminescence when exited by 980 nm laser. The highest PL intensities were obtained in La2O2S co-doped with 8 wt% Yb and 1.5 wt% Ho, or in case of La2O2S:Yb3+/Tm3+ with 4 wt% Yb and 0.5 wt% Tm.
The CIE 1976 chromaticity coordinates of Ho3+ photoluminescence emission are (0.119, 0.581), with color purity of 98.7 %. The chromaticity of upconversion emission was invariant to doping concentrations.
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•La2O2S:Yb3+/Tm3+ and La2O2S:Yb3+/Ho3+ were synthesized by the optimized combustion technique.•Microcrystalline sub-micron particles are in pure hexagonal phase and average 50 nm diameter.•Upconversion photoluminescence is typical for the doped lanthanide pair.
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