Luminescence thermometry has substantially progressed in the last decade, rapidly approaching the performance of concurrent technologies. Performance is usually assessed through the relative thermal sensitivity, Sr, and temperature uncertainty, δT. Until now, the state‐of‐the‐art values at ambient conditions do not exceed maximum Sr of 12.5% K−1 and minimum δT of 0.1 K. Although these numbers are satisfactory for most applications, they are insufficient for fields that require lower thermal uncertainties, such as biomedicine. This has motivated the development of materials with an improved thermal response, many of them responding to the temperature through distinct photophysical properties. This paper demonstrates how the performance of multiparametric luminescent thermometers can be further improved by simply applying new analysis routes. The synergy between multiparametric readouts and multiple linear regression makes possible a tenfold improvement in Sr and δT, reaching a world record of 50% K−1 and 0.05 K, respectively. This is achieved without requiring the development of new materials or upgrading the detection system as illustrated by using the green fluorescent protein and Ag2S nanoparticles. These results open a new era in biomedicine thanks to the development of new diagnosis tools based on the detection of super‐small temperature fluctuations in living specimens.

Liquid water, despite its simple molecular structure, remains one of the most fascinating and complex substances. Most notably, many questions continue to exist regarding phase transitions and anomalous properties of water, which are subtle to observe experimentally. Here, we report a sharp transition in water at 330 K unveiled through experimental measurements of the instantaneous Brownian velocity of NaYF4:Yb/Er upconversion nanoparticles in water. Our experimental investigations, corroborated by molecular dynamics simulations, elucidate a geometrical phase transition where a low-density-liquid (LDL) phase becomes percolated below 330 K. Around this critical temperature, we find that the sizes of the LDL clusters to be similar to the nanoparticles, confirming the role of upconversion nanoparticle as a powerful ruler for measuring the extensiveness of the LDL hydrogen-bond network and nanometer-scale spatial changes (20 to 100 nm) in liquids. Additionally, a new order parameter that unequivocally classifies water molecules into two local geometric states is introduced, providing a new tool for understanding and modelling water's many anomalous properties and phase transitions.

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Bacterial cellulose (BC) is a biocompatible and nontoxic biopolymer that has been successfully used as a substrate for flexible organic light emitting diodes (OLEDs). Although BC membranes exhibit excellent mechanical properties and industrial scalability, they are semitransparent, which limits their performance. To improve the optical properties of BC membranes, methods such as the polymerization of different inorganic–organic hybrid materials and petrochemical derivative monomers have been considered; however, these methods require considerable time and effort. In this work, transparent BC membranes for conformable OLEDs substrates are fabricated by spray coating a solution of recycled petrochemical plastics, found in expanded foam package wastes, and d‐limonene, which is a green solvent extracted from orange peels. This fabrication approach is highly scalable and can be considered a sustainable technique to develop high performance transparent substrates for photonic applications based on both recovered petrochemical polymers and naturally occurring biopolymers. In terms of the morphological and structural properties, the resulting transparent membranes exhibit a lower roughness than pristine BC. The resulting BC‐PS composite is used as a substrate for OLED fabrication. The conformable OLEDs exhibit a current efficiency of up to 5 cd A−1 (16 000 cd m−2) and power density of ≈2.8 mW cm−2.

Mesoporous silica nanoparticles prepared by organic template-driven synthesis have been successfully explored as carriers of the drug-derivate green luminescent complex of terbium (III) with the nonsteroidal anti-inflammatory drug ketoprofen. The terbium (III) complex was synthesized by reacting ketoprofen sodium salt with terbium (III) chloride, which was further adsorbed onto the surface of mesoporous nanoparticles with a mean particle size of 47 ± 4 nm and pore size of 11 nm. The incorporation of the complex into mesoporous silica nanoparticles was tracked by the decrease in the surface area and pore size of the nanoparticles, and successfully demonstrated by substantial changes in the adsorption isotherms and thermal and vibrational spectroscopy results. The cytotoxicity assay and confocal microscopy have shown that the novel luminescent nanohybrid presents high cell viability and the characteristic terbium (III) emission can be assessed through two-photon excitation, which paves the way for bioimaging applications in nanomedicine.

Quick‐response (QR) codes are gaining much consideration in recent years due to their simple and fast readability compared with conventional barcodes. QR codes provide increased storage capacity and safer access to information, fostering the development of optical or printed smart tags as preferred tools for the Internet of Things (IoT). Herein, the combination of Yb3+/Er3+‐doped NaGdF4 upconverting nanoparticles (UCNPs) with recovered plastic for the fabrication of sustainable screen‐printed QR codes is reported. Their photothermal response under distinct power densities of the 980 nm laser irradiation (15–115 W cm−2) induces color‐tuning and temperature sensing. This power dependence is exploited to design a double key molecular keylock accessed by a smartphone camera through the red (R), green (G), and blue (B) (RGB) additive color model and upconversion thermometry. The latter is based on the integrated areas of the 2H11/2→4I15/2 and 4S3/2→4I15/2 Er3+ transitions using the interconnectivity and integration into the IoT network of the mobile phone to download the temperature calibration curve of the UCNPs from a remote server. These findings illustrate the potential of QR codes‐bearing UCNPs toward the design of smart tags for mobile optical sensing and anticounterfeiting.

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 near‐infrared 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.

The combination of cellulosic materials and clays, such as Laponite, can provide composites with superior optical and mechanical properties compared to pristine cellulose. Synthetic clays can also be used as a host matrix for the immobilization of luminescent complexes, as the incorporated complexes may present enhanced emission quantum efficiency, photo and thermostability compared to the non-immobilized ones. In this way, we, herein, report the preparation of luminescent composites through the incorporation of a Eu(III) complex [Eu3+(tta)n] containing Laponite (Lap) into cellulose nanofibers (CNF). The thermogravimetry results show that the obtained CNF/Lap@[Eu3+(tta)n] films present higher thermal resistance than the CNF film. The Eu3+(tta)n species were found in the composite structure with preserved luminescence characteristics, and no leaching or degradation of the organic ligand was observed with the preparation of the composites.