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The anomalous behaviour of Eu3+ emission quenching on cooling is explained using experimental/theoretical approaches involving off-resonance excitation. Based on this, a highly sensitive CaTiO3:Eu3+,Er3+ phosphor (Sr = 4.9% K−1 at 83 K) was designed.

The synthesis of dual-emission nanocomposite materials has emerged as an excellent strategy for designing new and advanced luminescent ratiometric thermometers. In the present work, a dual-emission nanocomposite material based on carbon dots (CDots), with chitosan as the precursor, and Europium–Organic Framework (CDots/EuBDC) was prepared, through ultrasonic synthesis, and applied as a ratiometric thermometer. Whereas the as-synthesized nanocomposite maintains the crystalline structure of EuBDC, its thermal stability increases and the surface area decreases due to the CDots incorporation. The ratio of the CDots/EuBDC emission intensities (ICDots/IEu) is temperature-dependent in the 293 to 348 K range, in which the intensity of the Eu3+ 5D0 → 7F2 transition works as a reference signal. The CDots/EuBDC luminescent thermometer shows a maximum relative thermal sensitivity of 1.58% K−1 at 293 K and a colorimetric temperature response with (x, y) CIE color coordinates ranging from blue (0.36, 0.27), at 293 K, to orange (0.43, 0.30), at 343 K. published

Recent advances in light-emitting diode (LED) technology have created a new generation of energy-efficient light sources that is revolutionizing the lighting market. Due to the LED faster response, these devices can be used for illumination and for optical wireless communications, simultaneously, making visible light communication (VLC) a hot research topic worldwide. As the VLC link is free space, big challenges arise in its implementation. To improve the VLC performance, this work addresses cooperative communications by employing an optical amplifier. In this context, conjugated polymer incorporated into organic-inorganic hybrids with high quantum yield (>50%) were synthetized and processed as planar waveguides. The maximum gain efficiency values observed were 0.73±0.01cm $\mu \mathrm{J}^{-1}$, which is among the best ones known for conjugated polymers and hybrid materials. The waveguides were tested in a VLC test-in-bed scenario, showing a signal amplitude improvement of 1 dB, establishing the proposed approach as a promising cost-effective solution for optical amplification in VLCs.

The generation of temperature gradients on nanoparticles heated externally by a magnetic field is crucially important in magnetic hyperthermia therapy. But the intrinsic low heat i n g power of magnetic nanoparticles, at the conditions allowed for human use, is a limitation that restricts the general implementation of the technique. A promising alternative is local intracellular hyperthermia, whereby cell death (by apoptosis, necroptosis, or other mechanisms) is attained by small amounts of heat generated at thermosensitive intracellular sites. However , the few experiments conducted on the temperature determination of magnetic nanoparticles have found temperature increments that are much higher t h a n the theoretical predictions, thus supporting the local hyperthermia hypothesis. Reliable intracellular temperature measurements are needed to get an accurate picture and resolve the discrepancy. In this paper, we report the real-time variation of the local temperature on gamma-Fe2O3 magnetic nanoheaters using a Sm3+/Eu3+ ratiometric luminescent thermometer located on its surface during exposure to an external alternating magnetic field. We measure maximum temperature increments of 8 degrees C on the surface of the nanoheaters without any appreciable temperature increase on the cell membrane. Even with magnetic fields whose frequency and intensity are still well within health safety limits, these local temperature increments are sufficient to produce a small but noticeable cell death, which is enhanced considerably as the magnetic field intensity is increased to the maximum level tolerated for human use, consequently demonstrating the feasibility of local hyperthermia.

Novel luminescent In-based lead-free double halide perovskites co-doped with Yb3+/Er3+ have been synthesized. Their primary thermometer performance was assessed and their biological application to predict temperature was evaluated.

The application of nanoparticles in the biological context generally requires their dispersion in aqueous media. In this sense, luminescent nanoparticles are an excellent choice for minimally invasive imaging and local temperature sensing (nanothermometry). For these applications, nanoparticles must operate in the physiological temperature range (25–50 °C) but also in the nearinfrared spectral range (750–1800 nm), which comprises the three biological windows of maximal tissue transparency to photons. In this range, water displays several absorption bands that can strongly affect the optical properties of the nanoparticles. Therefore, a full understanding of the temperature dependence of water absorption in biological windows is of paramount importance for applications based on these optical properties. Herein, the absorption spectrum of water in the biological windows over the 25–65 °C temperature range is systematically analyzed, and its temperature dependence considering the coexistence of two states of water is interpreted. Additionally, to illustrate the importance of state-of-the-art applications, the effects of the absorption of water on the emission spectrum of Ag2S nanoparticles, the most sensitive luminescent nanothermometers for in vivo applications to date, are presented. The spectral shape of the nanoparticles’ emission is drastically affected by the water absorption, impacting their thermometric performance, This work was financed by the Spanish Ministerio de Ciencia e Innovación under project PID2019-106211RB-I00, by the Instituto de Salud Carlos III (PI19/00565), by the Comunidad Autónoma de Madrid (S2017/BMD3867 RENIM-CM) and co-financed by the European structural and investment fund. Additional funding was provided by the European Union Horizon 2020 FETOpen project NanoTBTech (801305), the Fundación para la Investigación Biomédica del Hospital Universitario Ramón y Cajal project IMP21_A4 (2021/0427), and by COST action CA17140. A.B. acknowledges funding support through the TALENTO 2019T1/IND14014 contract (Comunidad Autónoma de Madrid). F.E.M. and L.D.C. acknowledge the financial support received from the project Shape of Water (PTDC/NAN-PRO/3881/2020) through Portuguese funds

The design of molecular materials suitable for disparate fields could lead to new advances in engineering applications. In this work, a series of Ln3+-doped BiF3 sub-microparticles were synthesized through microwave-assisted synthesis. The effects of doping are evaluated from the structural and morphological viewpoint. In general, increasing the Ln3+ concentration the octahedral habitus is distorted to a spheric one, and some aggregates are visible without any differences in the crystalline phase. The optical response of the samples confirms that the BiF3 materials are suitable hosts for the luminescence of the tested trivalent lanthanide (Ln3+) ions (Ln = Eu, Tb, Tm, Ho, Er, Yb). A Yb3+/Er3+ co-doped sample is presented as an illustrative example of all-photonic molecular logic operations and primary luminescent thermometry.

The tetranuclear linear complex [Dy

International audience; We report here the synthesis, structure, luminescence, and magnetic properties of three new cage-like tetranuclear silsesquioxanes (Et 4 N) 2 [(PhSiO 1..5) 8 (Y 0.75 Dy 0.25 O 1.5) 4 (O)(NO 2.5) 6 (EtOH) 2 (MeCN) 2 ] and (Cat) 2 [(PhSiO 1.5) 8 (DyO 1.5) 4 (O)(NO 2.5) 6 (EtOH) 2 (MeCN) 2 ] (Cat=Et 4 N or Ph 4 P). They present a characteristic greenyellow emission. The Y 3+ /Dy 3+ compound displays in addition a field-induced Single Molecule Magnet (SMM) behavior making it the first reported bifunctional magneto-luminescent silsesquioxane.

Remote sensing through ratiometric luminescence thermometry based on trivalent lanthanide ions (Ln(III)) has lately become a promising technique due to its numerous applications. Most available Ln(III)-based luminescent thermometers require a calibration process with a reference thermal probe (secondary thermometers) and recurrent calibrations are mandatory, particularly when the thermometers are used in different media. This is sometimes impractical and a medium-independent calibration relation is postulated, which is potentially inaccurate. Thus, the determination of the temperature based on well-grounded physical principles by primary thermometers is the only way to overcome these challenges. Despite being considered one of the most important developments in luminescence thermometry, primary luminescent thermometers are scarce. Primary thermometers requiring calibration are proposed, implemented, and validated at one known temperature (primary-T), which are also self-referencing, employing ratiometric data from the excitation spectrum of Ln(III). By combining with the emission spectrum, thermometers not requiring calibration (primary-S) are devised. An Eu(III)-β-diketonate complex is used as a proof-of-concept, but the approach is universal and other Ln(III)-based materials can be explored. Because many thermometric parameters are employed for temperature prediction an unprecedented very high accuracy of 0.2% in the physiological range is obtained. published

Simultaneous fine-tune of magnetic and optical properties in lanthanide single-molecule magnets (SMMs) is a daunting task. Even more so when additional functionalities, like luminescence thermometry, are sought after. Herein, we explore the use of a ligand with both soft and hard donor atoms (thiobenzoate, tba−) as a strategy to prepare a multifunctional optomagnetic lanthanide complex. The proposed mononuclear Dy3+ complex acts as a zero-field SMM, whose energy barrier to magnetization reversal was confirmed from the analysis of the photoluminescence spectrum. Moreover, the temperature dependence of the emission spectral profile was harnessed to build a thermometric approach working below 12 K - where the complex behaves as an SMM. In search for general trends informing the preparation of similar multifunctional SMMs, we modelled the electronic properties of a series of complexes where the sulfur atom of tba− is replaced for other chalcogens (O, Se, Te). These calculations show that careful choice of ligands with soft donor atoms can boost both magnetic and thermometric performances, paving the way for the rational design of novel multifunctional lanthanide complexes. published

The hexagonal-phase (β) of NaREF4 upconversion nanocrystals (RE = rare earth elements) has been widely employed because of the outstanding luminescence performance, yet less is known about the essence of this superior property. The current understanding of this issue is raised from the advantage of weak electron–vibration interactions in fluoride systems, while the interpretability of this statement is controversial and contradictory results are commonly reported. One feasible way to solve this puzzle is from the aspect of “structure–property” relationship, yet even after decades of investigation, the structural details of β-NaREF4 are still under debate. Herein, the reported results relevant to this topic are reviewed, and the conflicting viewpoints are summarized. The similarities and differences between different lattice templates are assessed, and the reasons underlying the divergence are analysed. Based on these discussions, it is realized that the crystal structure of β-NaREF4 should be more reliably depicted as one flexible lattice framework with complex characteristics, and the structural disorder induced by atom displacements in the lattice is probably the key to supporting the superior luminescence properties of β-NaREF4 nanocrystals.

Photon upconversion taking place in small rare-earth-doped nanoparticles has been recently observed to be thermally modulated in an anomalous manner, showing thermal enhancement of the emission intensity. This effect was proved to be linked to the role of adsorbed water molecules as surface quenchers. Therefore, the surface capping of the particles has a direct influence on the thermal dynamics of water adsorption and desorption. Here, we show that the upconversion intensity of small-size (3+ and Er3+ ions, and functionalized with different capping molecules, present clear irreversibility patterns upon thermal cycling that strongly depend on the chemical nature of the nanoparticle surface. By performing temperature-controlled luminescence measurements we observed the formation of a thermal hysteresis loop, resembling an optical switching phenomenon, whose shape and trajectory depend on the hydrophilicity of the surface chemistry. Additionally, the formation of an intensity overshoot takes place immediately after turning off the heating source, affecting each radiative transition differently. We performed numerical modelling to understand this effect considering non-radiative energy transfer from surface defect states to the Er3+ ions. These findings are relevant for the comprehension of nanoparticle-based luminescence and the interplay between surface and volume effects, and more generally, for applications involving UCNPs such as nanothermometry, bioimaging, and the development of optical encoding systems., Financial support from the NanoTBtech European Union's Horizon 2020 FET Open programme under grant agreement no. 801305

Luminescence thermometers and manometers are among the most paramount emerging applications of phosphors nowadays, and remote reading is not the only attractive advantage they offer. Presently, truly encouraging examples offering both a wide operating range and appreciating thermal sensitivity are still limited. Double-mode sensors are especially attractive but pose additional problems to design them and control their properties. In this paper, we investigate Y2(Gex,Si1–x)O5:0.05 mol%Pr powder phosphors methodically varying the Ge : Si molar ratio to design their properties both in optical thermometry and manometry. We show that activation energy for thermal quenching of the 5d → 4f luminescence may be tuned and the mechanism of this process controlled. Consequently, fine-tuning of the luminescent properties important in thermometry may be managed. Specific properties of the 5d → 4f luminescence allow dual-mode thermometry to be executed using either luminescence intensity ratio or the emission decay kinetics for that purpose. The highest values of the thermometric relative sensitivity depend on the Ge : Si molar ratio and range from ∼2.5 to 3.5% K−1. The temperature range of the best performance may also be effectively tuned by adjusting the Ge : Si molar ratio. Controlling the Ge : Si proportion also allows the sensitivity of these phosphors in manometry to be improved. The Y2(Ge0.10,Si0.90)O5:0.05%Pr material presents the second-best ever reported sensitivity of 1.28 nm GPa−1. Consequently, the Y2(Gex,Si1–x)O5:0.05%Pr phosphors are useful for both temperature and pressure monitoring, and their performance in both functionalities may be effectively tuned by means of the Ge : Si molar ratio. Our findings may serve as a guide for researchers searching for novel optical thermometers and manometers.

The growing interest in the use of luminescence thermometry for noncontact temperature reading under very specific conditions imposes the need to develop an approach allowing modification of the luminescence parameters of a thermometer accordingly to requirements. Therefore, in response to these expectations, this manuscript reports an approach to modulate the spectral position and luminescence thermal quenching rate of Fe3+ ions by modifying the crystal field strength and the host material composition of nanocrystalline AB2O4 type nanocrystals (A = Mg, Ca; B = Al, Ga). It was proved that in a group of MgAl2O4, MgGa2O4, CaAl2O4, and CaGa2O4 nanocrystals doped with Fe3+ ions, the emission spectral range, as well as the relative thermal sensitivity (from 0.2%/°C for MAO to 2.07%/°C for CGO) and the operating temperature range, can be easily modified by the host material composition. For instance, a maximal relative thermal sensitivity of 2.58%/°C is obtained for Fe3+, Tb3+ co-doped CaAl2O4 nanocrystals. The proposed approach is a step toward the intentional designing of a highly sensitive luminescence thermometer.

New luminescent cage-like tetranuclear silsesquioxanes [NEt4][(Ph4Si4O8)2(Tb3Eu)(NO3)4(OH)(EtOH)3(H2O)]·4(EtOH) (1) and [NEt4]2[(Ph4Si4O8)2(Tb2Eu2)(NO3)6(EtOH)2(MeCN)2]·4(MeCN) (2) present a tunable thermosensitive Tb3+-to-Eu3+ energy transfer driven by Tb3+ and Eu3+ emission and may be used as temperature sensors operating in the range 41–100 °C with excellent linearity (R2 = 0.9990) and repeatability (>95%). The thermometer performance was evidenced by the maximum relative sensitivity of 0.63% °C−1 achieved at 68 °C.

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

Thermometry at the sub-microscale is a highly desired goal for the study of nanostructures and microbiological systems. Rare-earth doped upconversion nanoparticles constitute ideal elements to act as optical probes for the ratiometric measurement of the local temperature. In this work, we combine the ability of upconversion nanoparticles to operate as luminescent thermometers with hyperspectral microscopy to construct thermal images based on the heat dissipation of a percolating network of silver nanowires containing the nanoparticles under controlled electrical current flow. We quantify the electrothermal action by analyzing the hyperspectral data and constructing 2D maps for the emission intensity, the signal-to-noise ratio, and temperature, concluding that no significant thermal gradients were identified. The thermal evolution is clearly sensed by the upconversion nanoparticles, validating the use of this method for studying slow-dynamical thermal processes. We finally present a discussion about the accuracy of the thermal readings and the systematic limitations of the proposed method., This project has received funding from the European Union's Horizon 2020 FET Open programme under grant agreement No 801305 (NanoTBTech).

JOYSpectra is a free-of-charge web platform for perform online calculations of spectroscopic properties of lanthanide-based compounds and materials. It has several features and functionalities to provide a detailed analysis of the intensity parameters. For instance, their dependence with the chemical environment of the lanthanide ion such as structure and nature of ligating atoms, can be performed automatically and take into account covalency and thermal effects. The program can also calculate the intramolecular energy transfer rates from a single donor state (S1 or T1) up to 310 transitions involving 12 Ln3+ ions. The web platform was designed to be user-friendly for experimentalists and theoreticians interested in calculations and analysis of the photophysical behavior of lanthanides. Its use requires only the structure of the compound and the choices of a few calculation options. To show its easiness and usefulness, a detailed step-by-step calculation and analysis are performed for the [Ln(tta)3(H2O)2] (Ln: Eu3+ and Tb3+) complexes to explain and quantify their distinct luminescence., Financial support from the NanoTBtech European Union's Horizon 2020 FET Open programme under grant agreement no. 801305

Nanothermometry is the study of temperature at the submicron scale with a broad range of potential applications such as cellular studies or electronics. Molecular luminescent based nanothermometers offer a non-contact means to record these temperatures with high spatial resolution and thermal sensitivity. A luminescent based molecular thermometer comprised of visible-emitting Ga 3+ /Tb 3+ and Ga 3+ /Sm 3+ metallacrowns (MCs) achieved remarkable relative thermal sensitivity associated with very low temperature uncertainty of Sr=1.9 %K-1 and δT < 0.045 K, respectively, at 328 K, as an aqueous suspension of polystyrene nanobeads loaded with the corresponding MCs. They are so far the ratiometric molecular nanothermometers offering the highest level of sensitivity in the physiologically relevant temperature range. Nanothermometry is the analysis of the temperature of submicron systems. This domain of science offers potential applications in fields such as electronics, [1] microfluidics, [2] nanomedicine, [3] and cellular studies [4] where minimal spatial-sized thermometers are desired. Luminescence based thermometry correlates temperature with either emission intensity or emission lifetime changes of luminescent systems located in the studied environment. A low temperature uncertainty (δT) and a high relative thermal sensitivity of measurements (Sr) are desirable properties. Dual-centered ratiometric luminescent thermometry is a proven intensity-based method. In this technique, the intensity ratio (Δ) of two unique emitters' emission wavelengths provides a measurement of temperature with an internal calibration. [5] Molecular luminescence thermometry approaches what is perhaps the physical limit of attainable optical spatial resolution of temperature, restrained only by the diffraction limit of the optics used for detection. [6,7] It is difficult to generalize the parameters related to molecular thermometers, since while a system may excel in some respects it may be lacking in others. Molecular thermometers have been created using organic fluorescence dyes or transition metal complexes or clusters. [3,6,8-12] However, such systems have drawbacks since they usually exhibit limited photostability that depends on the intensity and duration of the light exposure, and can suffer from fluorescence intensity changes that are not related to variations of temperature but to modifications of pH, solvent viscosity or polarity, biological environment, or ionic strength. The wide emission bandwidths of organic reporters can complicate the interpretations of results in practical applications, and moreover, the luminescence lifetimes are most often used in the evaluation of temperature in such systems, with inherent drawbacks such as longer acquisition times and the requirement of rigorous post-processing data treatment as well as the inadequacy in mapping temperature gradients. [5] Lanthanide-based nanothermometers [13] may derive their functionality from the temperature-dependent luminescence of lanthanide cations (Ln 3+) in their compounds. Unique Ln 3+ photophysical properties originate from their core-like valence 4f electrons. These cations possess element-specific emission profiles with narrow bands the wavelengths of which are not affected by the experimental conditions. As most f-f transitions are forbidden, free Ln 3+ are very weakly absorbing resulting in low emission intensity. This limitation can be overcome through sensitization by an appropriate coordination environment. [14] While thermometers incorporating Ln 3+ are relatively common among metal-organic frameworks (MOFs) and other solid-state compounds

The experimental determination of the velocity of a colloidal nanoparticle (vNP) has recently became a hot topic. The thermal dependence of vNP is still left to be explored although it is a valuable source of information allowing, for instance, the discernment between ballistic and diffusive regimes. Optical tweezers (OTs) constitute a tool especially useful for the experimental determination of vNP although they have only been capable of determining it at room temperature. In this work, we demonstrate that it is possible to determine the temperature dependence of the diffusive velocity of a single colloidal nanoparticle by analyzing the temperature dependence of optical forces. The comparison between experimental results and theoretical predictions allowed us to discover the impact that the anomalous temperature dependence of water properties has on the dynamics of colloidal nanoparticles in this temperature range.

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...

Trivalent lanthanide ions (Ln3+) are used to prepare a plethora of coordination compounds, with metal-organic frameworks (MOFs) being among the most sought-after in recent years. The porosity of Ln-MOFs is often complemented by the luminescence imparted by the metal centers, making them attractive multifunctional materials. Here, we report a class of three-dimensional (3D) MOFs obtained from a solvothermal reaction between 2,6-naphthalenedicarboxylic acid (H2NDC) and lanthanide chlorides, yielding three types of compounds depending on the chosen lanthanide: [LnCl(NDC)(DMF)] for Ln3+ = La3+, Ce3+, Pr3+, Nd3+, Sm3+ (type 1), [Eu(NDC)1.5(DMF)]·0.5DMF (type 2), and [Ln2(NDC)3(DMF)2] for Ln3+ = Tb3+, Dy3+, Y3+, Er3+, Yb3+ (type 3). Photoluminescent properties of selected phases were explored at room temperature. The luminescence thermometry capability of Yb3+-doped Nd-MOF was fully investigated in the 15-300 K temperature range under 365 and 808 nm excitation. To describe the optical behavior of the isolated MOFs, we introduce the total energy-transfer balance model. Therein, the sum of energy-transfer rates is considered along with its dependence on the temperature - the sign, magnitude, and variation of this parameter - permitting to afford a thorough interpretation of the observed behavior of the luminescent species of all materials presented here. The combination of novel theoretical and experimental studies presented herein to describe energy-transfer processes in luminescent materials can pave the way toward the design of MOF-based chemical and physical sensors working in an optical range of interest for biomedical applications. Fil: Gomez, Germán Ernesto. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - San Luis. Instituto de Investigaciones en Tecnología Química. Universidad Nacional de San Luis. Facultad de Química, Bioquímica y Farmacia. Instituto de Investigaciones en Tecnología Química; Argentina Fil: Marin, Riccardo. University of Ottawa; Canadá Fil: Carneiro Neto, Albano N.. Universidade de Aveiro; Portugal Fil: Botas, Alexandre M. P.. Universidade de Aveiro; Portugal Fil: Ovens, Jeffrey. University of Ottawa; Canadá Fil: Kitos, Alexandros A.. University of Ottawa; Canadá Fil: Bernini, Maria Celeste. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - San Luis. Instituto de Investigaciones en Tecnología Química. Universidad Nacional de San Luis. Facultad de Química, Bioquímica y Farmacia. Instituto de Investigaciones en Tecnología Química; Argentina Fil: Carlos, Luís D.. Universidade de Aveiro; Portugal Fil: Soler Illia, Galo Juan de Avila Arturo. Universidad Nacional de San Martin. Instituto de Nanosistemas; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Murugesu, Muralee. University of Ottawa; Canadá