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The technology of lanthanide-based luminescent thermometers enabling remote optical temperature measurements is intensively developed. Sensors that allow the most precise, remote temperature readouts can be successfully used in biological, electronic, engineering and industrial processes. This work analyses the often-underestimated effect of excitation and detection geometry, as well as the sample thickness on the spectroscopic properties of the material and performance of the resulting luminescent thermometers. In the case of thick-layer samples, a significant change in the luminescence intensity ratios was observed compared to the thin-layer counterparts. This resulted in varying values of absolute and relative sensitivities for different sample thicknesses. The observed changes are assigned to a reabsorption effect, which is particularly significant for the thick-layer samples examined in the transmission (back-illuminated) geometry. The results presented in this work have very important implications on the accuracy of optical temperature monitoring via luminescence thermometry with Er3+ ions. [ABSTRACT FROM AUTHOR]

This work mainly focused on luminescence color tuning, white light generation and ultra-sensitive temperature sensing based on complex strontium vanadates doped with Eu3+ ions. A series of materials whose crystal structure changes from orthorhombic SrCO3, through hexagonal Sr5V3O13 and trigonal Sr3V2O8 to triclinic Sr2V2O7 were obtained via a modified sol–gel method, using altered vanadate to strontium ion ratios (V : Sr). Changes in the charge transfer band (CTB), characteristics of the Eu3+ ion emission and luminescence intensity changes were observed with an increasing content of vanadate groups in the materials. Dual-mode, excitation-dependent luminescence, white (λex = 345 nm) and red (λex = 393 nm), is observed. The luminescence color, chromaticity coordinates, color purity, quantum efficiency and emission correlated color temperature (CCT) of materials were compared. The application of the optimized Sr3V2O8:2%Eu3+ material as a multimodal temperature sensor is discussed. Temperature-dependent luminescence properties are investigated and an optical thermometer with high sensitivity is developed, revealing that the material has an extremely high spectral shift with a temperature of up to ∼0.862 nm K−1, currently classifying it as the most sensitive shift-based optical thermometer. Additionally, thanks to the capability of the developed phosphors for efficient energy conversion, we demonstrated their applicability in white-light generation for LED devices. [ABSTRACT FROM AUTHOR]

In this study, an optical thermometer based on regenerated cellulose fibers modified with YF3: 20% Yb3+, 2% Er3+ nanoparticles was developed. The presented sensor was fabricated by introducing YF3 nanoparticles into cellulose fibers during their formation by the so-called Lyocell process using N-methylmorpholine N-oxide as a direct solvent of cellulose. Under near-infrared excitation, the applied nanoparticles exhibited thermosensitive upconversion emission, which originated from the thermally coupled levels of Er3+ ions. The combination of cellulose fibers with upconversion nanoparticles resulted in a flexible thermometer that is resistant to environmental and electromagnetic interferences and allows precise and repeatable temperature measurements in the range of 298–362 K. The obtained fibers were used to produce a fabric that was successfully applied to determine human skin temperature, demonstrating its application potential in the field of wearable health monitoring devices and providing a promising alternative to thermometers based on conductive materials that are sensitive to electromagnetic fields. [ABSTRACT FROM AUTHOR]

Materials that generate pure, single-color emission are desirable in the development and manufacturing of modern optoelectronic devices. This work shows the possibility of generating pure, green up-conversion luminescence upon the excitation of Er3+-doped nanomaterials with a 785 nm NIR laser. The up-converting inorganic nanoluminophores YVO4: Er3+ and YVO4: Yb3+ and Er3+ were obtained using a hydrothermal method and subsequent calcination. The synthesized vanadate nanomaterials had a tetragonal structure and crystallized in the form of nearly spherical nanoparticles. Up-conversion emission spectra of the nanomaterials were measured using laser light sources with λex = 785 and 975 nm. Importantly, under the influence of the mentioned laser irradiation, the as-prepared samples exhibited bright green up-conversion luminescence that was visible to the naked eye. Depending on the dopant ions used and the selected excitation wavelengths, two (green) or three (green and red) bands originating from erbium ions appeared in the emission spectra. In this way, by changing the UC mechanisms, pure green luminescence of the material can be obtained. The proposed strategy, in combination with various single-doped UC nanomaterials activated with Er3+, might be beneficial for modern optoelectronics, such as light-emitting diodes with a rich color gamut for back-light display applications. [ABSTRACT FROM AUTHOR]

The absorption characteristics of lanthanide-based functional materials are of key importance for many scientists and engineers, e.g. in luminescence studies, bioimaging, optical heating/cooling, Raman spectroscopy, and industrial applications such as new light sources, optical sensors, labeling and tracing techniques, etc. Here we show the absorption spectra of solid, optically active lanthanide fluorides (CeF3, PrF3, NdF3, SmF3, EuF3, GdF3, TbF3, DyF3, HoF3, ErF3, TmF3, and YbF3) and oxides (CeO2, Pr6O11, Nd2O3, Sm2O3, Eu2O3, Gd2O3, Tb4O7, Dy2O3, Ho2O3, Er2O3, Tm2O3, and Yb2O3), measured in the UV-Vis-NIR range, from 200 to 2500 nm. The spectra were measured in diffused-reflectance mode using a spherical integrator. We assigned energy levels (2S+1LJ) of lanthanide ions(III), i.e. intraconfigurational 4f–4f transitions to the observed absorption bands. In order to clearly distinguish the 4f → 4f transitions, we also pointed out other absorption bands commonly observed in the measured spectra, such as intrinsic absorption of the matrices, interconfigurational 4f → 5d and charge transfer transitions, artificial bands from absorbed water (present in most materials) and a quartz holder. [ABSTRACT FROM AUTHOR]

In biomedical and optical applications, multifunctional upconverting nanoparticles (UCNPs) play an essential role where non‐invasive temperature sensing and imaging are necessary. UCNPs smaller than 20 nm, which can be excited under 808 nm wavelength, are particularly promising in this area and can be implemented in humans or other mammals. However, new versatile nanoprobes are still needed for biology, especially for challenging studies of small aquatic invertebrates. Such tools allow better monitoring and understanding of their physiology, biochemistry, and ecological responses, which is crucial due to the growing pollution of water reservoirs and climate change. Herein, multifunctional NaYF4:Yb3+, Er3+@NaNdF4:Yb3+ core@shell NPs (15 nm), forming stable aqueous colloids, exhibiting intense emissions under excitation in the first biological window (808 nm), and presenting high thermal sensitivity and resolution related to the thermally coupled energy levels of Er3+ ions, are designed and synthesized. Such properties of UCNPs are further utilized for optical imaging of aquatic invertebrates (Daphnia magna) and temperature detection inside their bodies under 808 nm excitation. This pioneering application of NaYF4:Yb3+, Er3+@NaNdF4:Yb3+ demonstrates the high potential of developed UCNPs for multifunctional applications, especially for bioimaging and temperature sensing within whole organisms. [ABSTRACT FROM AUTHOR]

Lanthanide-based luminescent nanothermometers play a crucial role in optical temperature determination. However, because of the strong thermal quenching of the luminescence, as well as the deterioration of their sensitivity and resolution with temperature elevation, they can operate in a relatively low-temperature range, usually from cryogenic to ≈800 K. In this work, we show how to overcome these limitations and monitor very high-temperature values, with high sensitivity (≈2.1% K -1 ) and good thermal resolution (≈1.4 K) at around 1000 K. As an optical probe of temperature, we chose upconverting Yb 3+ -Tm 3+ codoped YVO 4 nanoparticles. For ratiometric sensing in the low-temperature range, we used the relative intensities of the Tm 3+ emissions associated with the 3 F 2,3 and 3 H 4 thermally coupled levels, that is, 3 F 2,3 → 3 H 6 / 3 H 4 → 3 H 6 (700/800 nm) band intensity ratio. In order to improve sensitivity and resolution in the high-temperature range, we used the 940/800 nm band intensity ratio of the nonthermally coupled levels of Yb 3+ ( 2 F 5/2 → 2 F 7/2 ) and Tm 3+ ( 3 H 4 → 3 H 6 ). These NIR bands are very intense, even at extreme temperature values, and their intensity ratio changes significantly, allowing accurate temperature sensing with high thermal and spatial resolutions. The results presented in this work may be particularly important for industrial applications, such as metallurgy, catalysis, high-temperature synthesis, materials processing and engineering, and so forth, which require rapid, contactless temperature monitoring at extreme conditions.

Luminescent lanthanide fluoride core-shell (LaF 3 :Tb 3+ ,Ce 3+ @SiO 2 -NH 2 ) nanoparticles, with acetylsalicylic acid (aspirin) coated on the surface have been obtained. The synthesized products, which combine the potential located in the silica shell with the luminescent activity of the core, were characterized in detail with the use of luminescence spectroscopy, Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), and transmission electron microscopy (TEM) methods. The in vitro effects of the modified luminescent nanoparticles on human red blood cell (RBC) membrane permeability, RBC shape, and sedimentation rate were investigated to assess the hemocompatibility of the obtained compounds. This study demonstrates that LaF 3 : Tb 3+ 5 %, Ce 3+ 10 %@SiO 2 -NH 2 nanoparticles with acetylsalicylic acid (aspirin) coated on the surface are very good precursors for multifunctional drug-delivery systems or bio-imaging probes that can be used safely in potential biomedical applications., (© 2020 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Upconverting core@shell type β-NaYF 4 :Yb 3+ -Er 3+ @SiO 2 nanorods have been obtained by a two-step synthesis process, which encompasses hydrothermal and microemulsion routes. The synthesized nanomaterial forms stable aqueous colloids and exhibits a bright dual-center emission (λ ex = 975 nm), i.e., upconversion luminescence of Er 3+ and down-shifting emission of Yb 3+ , located in the first (I-BW) and the second (II-BW) biological windows of the spectral range, respectively. The intensity ratios of the emission bands of Er 3+ and Yb 3+ observed in the vis-near-infrared (NIR) range monotonously change with temperature, i.e., the thermalized Er 3+ levels ( 2 H 11/2 → 4 I 15/2 / 4 S 3/2 → 4 I 15/2 ) and the nonthermally coupled Yb 3+ /Er 3+ levels ( 2 F 5/2 → 2 F 7/2 / 4 I 9/2 → 4 I 15/2 or 4 F 9/2 → 4 I 15/2 ). Hence, their thermal evolutions have been correlated with temperature using the Boltzmann type distribution and second-order polynomial fits for temperature-sensing purposes, i.e., Er 3+ 525/545 nm (max S r = 1.31% K -1 ) and Yb 3+ /Er 3+ 1010/810 nm (1.64% K -1 ) or 1010/660 nm (0.96% K -1 ). Additionally, a fresh chicken breast was used as a tissue imitation in the performed ex vivo experiment, showing the advantage of the use of NIR Yb 3+ /Er 3+ bands, vs. the typically used Er 3+ 525/545 nm band ratio, i.e., better penetration of the luminescence signal through the tissue in the I-BW and II-BW. Such nanomaterials can be utilized as accurate and effective, broad-range vis-NIR optical, contactless sensors of temperature.

A novel, contactless optical sensor of pressure based on the luminescence red-shift and bandwidth (full width at half-maximum, fwhm) of the Ce 3+ -doped fluorapatite-Y 6 Ba 4 (SiO 4 ) 6 F 2 powder has been successfully synthesized via a facile solid-state method. The obtained material exhibits a bright blue emission under UV light excitation. It was characterized using powder X-ray diffraction, scanning electron microscopy and luminescence spectroscopy, including high-pressure measurements of excitation and emission spectra, up to above ∼30 GPa. Compression of the material resulted in a significant red-shift of the allowed 4f → 5d and 5d → 4f transitions of Ce 3+ in the excitation and emission spectra, respectively. The pressure-induced monotonic shift of the emission band, as well as changes in the excitation/emission band widths, have been correlated with pressure for sensing purposes. The material exhibits a high pressure sensitivity (dλ/d P ≈ 0.63 nm/GPa) and outstanding signal intensity at high-pressure conditions (∼90% of the initial intensity at around 20 GPa) with minimal pressure-induced quenching of luminescence.