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In thiswork, we investigate the influence of Mn2+ on the emission color, thermal sensing and optical heater behavior of NaGdF4: Yb/Er nanophosphors, which the nanoparticles were synthesized by a hydrothermal method using oleic acid as both a stabilizing and a chelating agent. The morphology and crystal size of upconversion nano particles (UCNPs) can be effectively controlled through the addition of Mn2+ dopant contents in NaGdF4: Yb/Er system. Moreover, an enhancement in overall UCL spectra of Mn2+ doped UCNPs for NaGdF4 host compared to the UCNPs is observed, which results from a closed back-energy transfer between Er3+ and Mn2+ ions (4S3/2 (Er3+) → 4T1 (Mn2+) → 4F9/2 (Er3+)). The temperature sensitivity of NaGdF4:Yb3+/Er3+ doping with Mn2+ based on thermally coupled levels (2H11/2 and 4S3/2) of Er3+ is similar to that particles without Mn2+ in the 303–548 K range. And the maximum sensitivity is 0.0043 K−1 at 523 K for NaGdF4:Yb3+/Er3+/Mn2+. Interestingly, the NaGdF4:Yb3+/Er3+/Mn2+ shows preferable optical heating behavior, which is reaching a large value of 50 K. These results indicate that inducing of Mn2+ ions in NaGdF4:Yb3+/Er3+ nanophosphors has potential in colorful display, temperature sensor.

Abstract Nd3+‐doped near‐infrared (NIR) luminescent nanocrystals (NCs) have shown great promise in various bioapplications. A fundamental understanding of the electronic structures of Nd3+ in NCs is of vital importance for discovering novel Nd3+‐activated luminescent nanoprobes and exploring their new applications. Herein, the electronic structures of Nd3+ in LiLuF4 NCs are unraveled by means of low‐temperature and high‐resolution optical spectroscopy. The photoactive site symmetry of Nd3+ in LiLuF4 NCs and its crystal‐field (CF) transition lines in the NIR region of interest are identified. By taking advantage of the well‐resolved and sharp CF transition lines of Nd3+, the application of LiLuF4:Nd3+ NCs as sensitive NIR‐to‐NIR luminescent nanoprobes for ratiometric detection of cryogenic temperature with a linear range of 77–275 K is demonstrated. These findings reveal the great potential of LiLuF4:Nd3+ NCs in temperature sensing and also lay a foundation for future design of efficient Nd3+‐based luminescent nanoprobes.

Multifunctional sensors have played a crucial role in constructing high-integration electronic networks. Most of the current multifunctional sensors rely on multiple materials to simultaneously detect different physical stimuli. Here, we demonstrate the large piezo-pyroelectric effect in ferroelectric Pb(Mg 1/3 Nb 2/3 )O 3 -PbTiO 3 (PMN-PT) single crystals for simultaneous pressure and temperature sensing. The outstanding piezoelectric and pyroelectric properties of PMN-PT result in rapid response speed and high sensitivity, with values of 46 ms and 28.4 nA kPa -1 for pressure sensing, and 1.98 s and 94.66 nC °C -1 for temperature detection, respectively. By leveraging the distinct differences in the response speed of piezoelectric and pyroelectric responses, the piezo-pyroelectric effect of PMN-PT can effectively detect pressure and temperature from mixed-force thermal stimuli, which enables a robotic hand for stimuli classification. With appealing multifunctionality, fast speed, high sensitivity, and compact structure, the proposed self-powered bimodal sensor therefore holds significant potential for high-performance artificial perception.

The unique properties of upconversion nanoparticles (UCNPs) are responsible for their diverse applications in photonic materials, medicine, analytics, and energy conversion. In this study, water-soluble rare-earth upconversion nanomaterials emitting green, yellow, and red light under 1550 nm excitation were synthesized. These nanomaterials were then integrated into water-soluble Kevlar nanofibers (KNFs) to fabricate ultra-thin composite films exhibiting favorable mechanical characteristics. The characterization of the products, along with their luminescent, mechanical, and temperature-sensing properties, was examined. The results indicate that the composite material exhibited varying colors based on the doped nanoparticles when subjected to 1550 nm excitation. The composite showed highly sensitive temperature-sensing properties, excellent luminescent characteristics, and superior mechanical strength. This study suggests that KNFs are effective carriers of UCNPs. This study offers a reference for the utilization of rare-earth upconversion in anti-counterfeiting displays, wearable health monitoring, and remote temperature sensing.

The present work intends to provide a closer look at histamine in Drosophila . This choice is motivated firstly because Drosophila has proven over the years to be a very simple, but powerful, model organism abundantly assisting scientists in explaining not only normal functions, but also derangements that occur in higher organisms, not excluding humans. Secondly, because histamine has been demonstrated to be a pleiotropic master molecule in pharmacology and immunology, with increasingly recognized roles also in the nervous system. Indeed, it interacts with various neurotransmitters and controls functions such as learning, memory, circadian rhythm, satiety, energy balance, nociception, and motor circuits, not excluding several pathological conditions. In view of this, our review is focused on the knowledge that the use of Drosophila has added to the already vast histaminergic field. In particular, we have described histamine's actions on photoreceptors sustaining the visual system and synchronizing circadian rhythms, but also on temperature preference, courtship behavior, and mechanosensory transmission. In addition, we have highlighted the pathophysiological consequences of mutations on genes involved in histamine metabolism and signaling. By promoting critical discussion and further research, our aim is to emphasize and renew the importance of histaminergic research in biomedicine through the exploitation of Drosophila , hopefully extending the scientific debate to the academic, industry, and general public audiences.

Hydrogen-bonded organic frameworks (HOFs) have shown promise in various fields; however, the construction of HOF/polymer hybrid membranes that can maintain both structural and functional integrity remains challenging. In this study, we here fabricated a new HOF (HOF-50) with reserved polymerizable allyl group via charge-assisted H-bonds between the carboxylate anion and amidinium, and subsequently copolymerized the HOF with monomers to construct a covalently bonded HOF/polymer hybrid (polyHOF) membrane. The resulting polyHOF membrane not only exhibits customizable mechanical properties and extreme stability, but also shows an exceptional ratiometric luminescent temperature-sensing function with very high sensitivity and visibility even when the lanthanide content is two orders of magnitude lower than that of the reported mixed-lanthanide metal-organic frameworks (MOFs) and lanthanide-doped covalent organic frameworks (COFs). This orthogonal postsynthesis copolymerization strategy may provide a general approach for preparing covalently connected HOF/polymer hybrid membranes for diverse applications., (© 2024 Wiley-VCH GmbH.)

Transdermal drug delivery has emerged as an alternative to conventional drug delivery systems as it enables painless and convenient drug administration. However, next-generation healthcare systems need to facilitate "on-demand" delivery operations and should be highly efficient to penetrate the physiological barriers in the skin. Here, we report an ultrathin dye-loaded epidermal tattoo (UDET) that allows wirelessly stimulated drug delivery with high efficiency. The UDET consists of an electrospun dye-loaded silk nanofiber mat and a covered carbon nanotube (CNT) layer. UDETs are conformally tattooed on pigskins and show stable operation under mechanical deformation. Biological fluorescence dyes such as vitamin B 12 , riboflavin, rhodamine B, and sodium fluorescein are applied as model drugs. Illuminating the UDET by a low-power light-emitting diode (< 34.5 mW/cm 2 ) triggers transdermal drug delivery due to heat generation. The CNTs convert the absorbed light into heat, and then the dyes loaded on silk can be diffused through the epidermis. The CNT layer is electrically conductive and can detect the temperature by reading the resistance change (0.1917 Ω/°C). This indicates that the UDET can be used simultaneously to read temperature and deliver the loaded dye molecules, making it a promising on-demand drug delivery strategy for future medicine technology., Supplementary Information: The online version contains supplementary material available at 10.1007/s13534-024-00363-6., Competing Interests: Conflict of interestThe authors declare that they have no known competing interests or personal relationships that could have appeared to influence the work reported in this paper., (© Korean Society of Medical and Biological Engineering 2024. Springer Nature or its licensor (e.g. a society or other partner) holds exclusive rights to this article under a publishing agreement with the author(s) or other rightsholder(s); author self-archiving of the accepted manuscript version of this article is solely governed by the terms of such publishing agreement and applicable law.)

A flexible sensor that simultaneously senses temperature and pressure is crucial in various fields, such as human-machine interaction, artificial intelligence, and biomedical applications. Previous research has mainly focused on single-function flexible sensors for e-skins or smart devices, and integrated bimodal sensing of temperature and pressure without complex crosstalk decoupling algorithms remains challenging. In this work, a flexible bimodal sensor is proposed that utilizes spatial orthogonality between in-plane thermoelectricity and out-plane piezoresistivity, which enables fully decoupled temperature-pressure sensing. The proposed bimodal sensor exhibits a high sensitivity of 281.46 µV K -1 for temperature sensing and 2.181 kPa -1 for pressure sensing. In the bimodal sensing mode, the sensor exhibits negligible mutual interference, providing a measurement error of ± 7% and ± 8% for temperature and pressure, respectively, within a 120 kPa pressure range and a 40 K temperature variation. Additionally, simultaneous spatial mapping of temperature and pressure with a bimodal sensor array enables contact shape identification with enhanced accuracy beyond the limit imposed by the number of sensing units. The proposed integrated bimodal sensing strategy does not require complex crosstalk decoupling algorithms, which represents a significant advancement in flexible sensors for applications that necessitate simultaneous sensing of temperature and pressure., (© 2023 Wiley‐VCH GmbH.)

Objective: The objective of this study is to assess the impact of overnight environmental conditions on erectile penile temperature within a controlled setting, with the aim of investigating the feasibility of using temperature measurements for nocturnal erection detection in erectile dysfunction diagnostics., Subjects/patients and Methods: We conducted a proof-of-concept study involving 10 healthy male participants aged 20 to 25. The study was carried out at the Department of Urology, St. Antonius Ziekenhuis, the Netherlands. Penile temperature thermistor measurements were taken during visually aroused erections of participants in naked state and in simulated overnight condition (underwear and blankets). Main outcome variables were peak and baseline temperature during erectile periods. To minimize the impact of differences in erectile strength and duration between consecutive measurements, we applied randomization to the order of the environmental conditions., Results: We observed a significant increase in penile temperature during erection in both the naked ( p  < 0.01) and simulated overnight condition ( p  < 0.01). The mean temperature increase was 1.70 and 0.67 ° C, respectively. While penile temperature returned to baseline immediately after naked erections, the 'Staying Hot effect' was noted in the simulated overnight condition measurements, where the temperature remained elevated at peak temperature for the entire 30-min period following the erection., Conclusions: The findings from this study indicate that the penile temperature not only significantly increases during naked sexual arousal but is also detectable under simulated overnight conditions. This underscores the potential of using temperature measurements for nocturnal erection detection, representing a crucial initial step in developing a modernized, non-invasive sensor system for ambulatory erectile dysfunction diagnostics. Further research, including an overnight study, is needed to gain insights into the feasibility of utilizing penile temperature measurements for nocturnal erection detection and to assess the impact of the 'Staying Hot effect' on subsequent erection detection., Competing Interests: There are no conflicts of interest associated with this study. This study was funded by the St. Antonius Ziekenhuis and University of Twente as part of an academic dissertation study. None of these organizations may gain or lose financially through this publication. The funding source had no further involvement in the study. No financial benefits or support was received from the distributors of the components of the penile temperature measurement system. There is no (desired) patent holding or stock ownership that could cause conflict of interest., (© 2024 The Authors. BJUI Compass published by John Wiley & Sons Ltd on behalf of BJU International Company.)

This research presents the design and implementation of a chipless Radio Frequency Identification (RFID) multi-sensor tag on a flexible laminate. Along with the tag's primary function of data encoding for object identification purposes, the tag also incorporates moisture and temperature sensing functionalities within a compact size measuring a mere 15 × 16 mm 2 . The tag structure comprises of a total 29 resonators, with each resonator corresponding to one bit in the microwave response. The initial design utilized the bendable Rogers RT/duroid®5880 within a frequency band of 5.48-28.87 GHz. To conduct a comprehensive comparative analysis, the tag design is optimized for two distinct substrates including Kapton®HN and PET. The optimization process involves exploring the utilization of both silver nanoparticle-based ink and Aluminum as radiators. The sensing feature was incorporated by deploying a thin film of Kapton®HN over the longest slot of the tag which acts as a moisture sensor. Temperature sensing feature was achieved by combining Stanyl® polyamide, a temperature dependent polymer, with Rogers RT/duroid®5880 which served as a fused substrate. The tag showcases a high code density of 12.08 bits/cm 2 enabling it to efficiently label 2 29 unique items. Its unique features include flexibility, miniaturized design, printability, cost-effectiveness and multi sensing property., Competing Interests: The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (© 2024 The Authors.)

In this work, a plasmonic sensor based on metal-insulator-metal (MIM) waveguide for temperature sensing application is numerically investigated via finite element method (FEM). The resonant cavity filled with PDMS polymer is side-coupled to the MIM bus waveguide. The sensitivity of the proposed device is ~ - 0.44 nm/°C which can be further enhanced to - 0.63 nm/°C by embedding a period array of metallic nanoblocks in the center of the cavity. We comprehend the existence of numerous highly attractive and sensitive plasmonic sensor designs, yet a notable gap exists in the exploration of light coupling mechanisms to these nanoscale waveguides. Consequently, we introduced an attractive approach: orthogonal mode couplers designed for plasmonic chips, which leverage MIM waveguide-based sensors. The optimized transmission of the hybrid system including silicon couplers and MIM waveguide is in the range of - 1.73 dB to - 2.93 dB for a broad wavelength range of 1450-1650 nm. The skillful integration of these couplers not only distinguishes our plasmonic sensor but also positions it as a highly promising solution for an extensive array of sensing applications., (© 2024. The Author(s).)

Highly sensitive and flexible composite sensors with pressure and temperature sensing abilities are of great importance in human motion monitoring, robotic skins, and automobile seats when checking the boarding status. Several studies have been conducted to improve the temperature-pressure sensitivity; however, they require a complex fabrication process for micro-nanostructures, which are material-dependent. Therefore, there is a need to develop the structural designs to improve the sensing abilities. Herein, we demonstrate a flexible composite with an enhanced pressure and temperature sensing performance. Its structural design consists of a multilayered composite construction with an elastic modulus gradient. Controlled stress concentration and distribution induced by a micropatterned structure between the layers improves its pressure and temperature sensing performance. The proposed composite sensor can monitor a wide range of pressure and temperature stimuli and also has potential applications as an automotive seat sensor for simultaneous human temperature detection and occupant weight sensing.

Nickel manganite nanocrystalline fibers were obtained by electrospinning and subsequent calcination at 400 °C. As-spun fibers were characterized by TG/DTA, Scanning Electron Microscopy and FT-IR spectroscopy analysis. X-ray diffraction and FT-IR spectroscopy analysis confirmed the formation of nickel manganite with a cubic spinel structure, while N2 physisorption at 77 K enabled determination of the BET specific surface area as 25.3 m2/g and (BJH) mesopore volume as 21.5 m2/g. The material constant (B) of the nanocrystalline nickel manganite fibers applied by drop-casting on test interdigitated electrodes on alumina substrate, dried at room temperature, was determined as 4379 K in the 20–50 °C temperature range and a temperature sensitivity of −4.95%/K at room temperature (25 °C). The change of impedance with relative humidity was monitored at 25 and 50 °C for a relative humidity (RH) change of 40 to 90% in the 42 Hzπ1 MHz frequency range. At 100 Hz and 25 °C, the sensitivity of 327.36 ± 80.12 kΩ/%RH was determined, showing that nickel manganite obtained by electrospinning has potential as a multifunctional material for combined humidity and temperature sensing.

In recent years, upconversion (UC) luminescence has attracted considerable attention because of its potential application in temperature measurement. In this work, LaNbO4:Er3+/Yb3+ phosphors are synthesized using a solid-state method. The x-ray diffraction patterns show that the phosphors obtained exhibit a single monoclinic structure, and doping does not change the crystal structure. Intense green and red emissions are observed upon 980-nm excitation. The emission intensity varies with the doping concentration, and the best doping concentrations are 1 mol.% and 10 mol.% for Er3+ and Yb3+ ions, respectively. The possible luminescence mechanism is investigated based on the UC emission dependence on pump power. The temperature-sensing ability is also investigated based on the fluorescence intensity ratio between two thermally coupled levels 2H11/2 and 4S3/2. The maximum sensitivity achieved is 0.81% K−1 at around 430 K, suggesting that the phosphor is a potential candidate for temperature sensing applications. [ABSTRACT FROM AUTHOR]

We proposed a new strategy for utilizing rare‐earth–free‐activated self‐referencing optical material with dual activators for temperature sensing, which was synthesized by conventional high‐temperature solid‐state method and was scarcely reported. Originating from the different thermal responses of Mn4+ and Bi3+ ions, a Mn4+/Bi3+‐based dual‐emitting fluorescence intensity ratio (FIR) as dual‐modal temperature signal for temperature sensing has been corroborated as a promising temperature sensing method. Due to the outstanding thermal resistance of activator Mn4+ (anti‐Stokes) benefiting from the unique 3dn electronic configurations and strong field strength of host, together with the energy transfer from Bi3+ to Mn4+ ions and excellent thermal quenching of Bi3+, this temperature‐sensitive phosphor displayed both an extensive detection temperature region ranging from 303 to 563 K and excellent absolute and relative sensitivity of 0.0147 K−1 and 1.21% K−1 respectively, both of which are higher than some foregoing reported optical materials. Furthermore, two well‐separated emission peaks at blue and red regions enabled an excellent signal discriminability and accurate temperature detection under the single‐wavelength excitation of 340 nm. In addition, freedom from rare‐earth ions contributed its possibility to be mass‐produced for meeting the needs of economic rationality, nontoxic and convenient synthesis. It is anticipated that this preliminary study would arouse peoples' attention on exploring more novel dual activator‐based optical thermometric materials in absence of rare‐earth ions. [ABSTRACT FROM AUTHOR]

In this paper, we introduce the need for real-time temperature monitoring in battery packs used in automotive applications so to have an accurate estimation of battery life and performances. Advanced energy storage management systems should sense operating and ambient temperature of battery packs in order to implement proper strategies to improve the efficiency of charge and discharge processes and to extend battery life. The proposed evaluation technique is based on an innovative and dynamic circuital model, which allows to accurately represent the functioning of a battery pack (in charge and discharge) in the various operating conditions. Each circuital parameter of the model has a well-defined function which highlights its dependence on temperature, state of charge, state of health and number of cells. The model characterization has been made through tests on different battery sets. A climatic chamber has been used to simulate different operating conditions of ambient temperature. The analysis of the parameters evolution in time has led to the identification of an ideal ambient temperature range for the type of batteries under examination in order to improve their performances over time in terms of energy efficiency and extension of useful life. [ABSTRACT FROM AUTHOR]

In this paper, a dual-mode (DM) micromechanical elliptical ring resonator for use in temperature sensing is reported. The proposed resonator is made of single crystal silicon and works based on beat frequency (fb). In the designed sensor, temperature coefficient of beat frequency (TCfb) will be increased significantly by minimizing the fb and provides better temperature sensitivity. This proposed device was designed and simulated by COMSOL Multyphysics software. By engineering the device geometry, we introduce two adjacent resonant frequencies which produce very small fb in the range of 2 kHz. The device shows TCf1 of about 44 ppm/ºC and TCf2 of 5 ppm/ºC. Combination of small fb and large ΔTCf, present temperature coefficient of beat frequency (TCfb) about 112000 ppm/ºC which has approximately 75× improvement in TCfb compared to previous demonstrated DM resonators. [ABSTRACT FROM AUTHOR]

For achieving well-performing optical thermometry, a new type of dual-mode optical thermometer is explored based on the valley-to-peak ratio (VPR) and fluorescence lifetime of Eu3+ emissions in the ZrO2:Eu3+ nanocrystals with sizes down to 10 nm. In the VPR strategy, the intensity ratio between the valley (600 nm) generated by the emission band overlap and the 606 nm peak (5D0→7F2), which is highly temperature sensitive, is employed, giving the maximum relative sensing sensitivity (Sr) of 1.8% K−1 at 293 K and good anti-interference performance. Meanwhile, the 606 nm emission exhibits a temperature-dependent decay lifetime with the highest Sr of 0.33% K−1 at 573 K, which is due to the promoted nonradiative relaxation with temperature. These results provide useful information for constructing high-performance dual-mode optical thermometers, which may further stimulate the development of photosensitive nanomaterials for frontier applications. [ABSTRACT FROM AUTHOR]

Featured Application: Multi-task learning; multi-parameter luminesce sensing. The classical approach to non-linear regression in physics is to take a mathematical model describing the functional dependence of the dependent variable from a set of independent variables, and then using non-linear fitting algorithms, extract the parameters used in the modeling. Particularly challenging are real systems, characterized by several additional influencing factors related to specific components, like electronics or optical parts. In such cases, to make the model reproduce the data, empirically determined terms are built in the models to compensate for the difficulty of modeling things that are, by construction, difficult to model. A new approach to solve this issue is to use neural networks, particularly feed-forward architectures with a sufficient number of hidden layers and an appropriate number of output neurons, each responsible for predicting the desired variables. Unfortunately, feed-forward neural networks (FFNNs) usually perform less efficiently when applied to multi-dimensional regression problems, that is when they are required to predict simultaneously multiple variables that depend from the input dataset in fundamentally different ways. To address this problem, we propose multi-task learning (MTL) architectures. These are characterized by multiple branches of task-specific layers, which have as input the output of a common set of layers. To demonstrate the power of this approach for multi-dimensional regression, the method is applied to luminescence sensing. Here, the MTL architecture allows predicting multiple parameters, the oxygen concentration and temperature, from a single set of measurements. [ABSTRACT FROM AUTHOR]

Rayleigh backscattering-based distributed fiber optic sensing technology is well known and widely used for large-scale structural health monitoring. Inspired by the Rayleigh backscattering-based sensing methodology on an optical fiber, in this paper, we present a sensing concept based on the random inhomogeneities on a coaxial cable. As an analogy of Rayleigh backscattering along an optical fiber length, “backscattering” also exists from a commercial coaxial cable due to its inherent defects along a cable length which induce a local variation (i.e., impedance mismatch). This is because of the irregular microscopic structures of the inner/outer conductors, and the inhomogeneous density or permittivity of the inner dielectrics after the cables are manufactured. The accumulated backscattered signals along the coaxial cable can be obtained using frequency-domain reflectometry. By analyzing the shift in the local backscattered signal, the local environmental perturbations (e.g., local strain or temperature) can be determined, so that truly distributed sensing capability using a coaxial cable can be achieved. To verify the proposed concept, an intact and commercial coaxial cable was demonstrated for distributed temperature sensing. Compared with the existing coaxial cable-based distributed sensing technologies, the proposed sensing concept does not need extra modifications to the coaxial cable and offers a truly distributed sensing capability. [ABSTRACT FROM AUTHOR]

• Simultaneous measurement of RH and temperature based on FBG and MMI. • The balloon-like sensing structure is with up-tapered MZI inner embedded. • The diameter of balloon-like structure is 3.0 cm. • The balloon-like sensing structure can easily be used in practical application. Fiber Bragg grating (FBG) cascaded with balloon-like sensing structure with up-tapered Mach-Zehnder interferometer (MZI) inner embedded is proposed and experimentally investigated for relative humidity (RH) and temperature measurement. The up-tapered MZI is formed by splicing a section of no-core fiber (NCF) between two sections of single mode fiber (SMF) to inspire cladding mode. The diameter of the balloon-like sensing structure adopted in this letter is 3.0 cm after optimization. RH measurement is carried out at room temperature, and the sensitivity is 6.1 pm/%RH in the range of 9.73–80.37 %RH. Meanwhile, the temperature sensitivity is 11 pm/°C in the range of 15.9–26.2 °C. Compared with transmission sensing structure, the balloon-like sensing structure makes it easier to contact with measurement environment in practical application. In addition, the proposed sensor is simple manufacture technology and low cost. [ABSTRACT FROM AUTHOR]

NaLa(MoO 4) 2 : Tb3+, Eu3+ phosphors were prepared via the hydrothermal method using sodium citrate as chelating agent, and different morphologies of the samples were obtained through the change of the Na 3 Cit molar ratio to rare earth ions. The NaLa(MoO 4) 2 : Tb3+, Eu3+ phosphors' structure, morphology, and temperature sensing performance were investigated using XRD (X-ray diffraction) and FE-SEM (Field Emission Scanning Electron Microscope) as well as temperature-dependent emission spectra. The XRD demonstrated that all the materials are body-centered tetragonal phase. The FE-SEM results show that a dosage of sodium citrate could control the NaLa(MoO 4) 2 : Tb3+, Eu3+ phosphors' morphology. On the basis of the temperature-dependent emission spectra, the FIR (Fluorescence Intensity Ratio) of Eu3+ and Tb3+ in all the samples changed with the temperature and could represent the temperature. Furthermore, the phosphors' sensitivity increased with the value of Cit3−/Re3+. Simultaneously, observed from the CIE (Commission International del'Eclairage) chromaticity coordinates, the range of the samples' luminescence color variation expanded with the Cit3−/Re3+ increases. [ABSTRACT FROM AUTHOR]

Eu2+/Eu3+ co-doped Sr 3 P 4 O 13 phosphors were prepared by high temperature solid stated method in air atmosphere and studied in detail their luminescent properties in order to investigate the possible applications in temperature sensors. The broadband emission of Eu2+ ions and the linear emission band of Eu3+ ions can be observed in the photoluminescence (PL) spectra of Sr 3 P 4 O 13 : Eu2+/Eu3+ phosphors due to the self-reduction effect. X-ray photoelectron spectroscopy (XPS), PL spectra, and time-resolved fluorescence lifetime confirm the formation of double emission centers of Eu2+ and Eu3+ ions in Sr 3 P 4 O 13 because of the self-reduction by charge compensation. In the Eu2+/Eu3+ co-activated Sr 3 P 4 O 13 thermometric phosphor, the blue emission of Eu2+ ions and red emission of Eu3+ ions, can be used as fluorescence intensity ratio (FIR) signals. In addition, the mechanism is discussed in detail based on the experimental data, and the strong temperature dependence is explained from the point of view of thermal quenching. Additionally, benefited from their diverse thermal quenching behavior, the FIR of Eu3+ to Eu2+ is fitted very well, and S a reached a maximum 0.008 K−1 at 573 K, while S r reached a maximum of 1.06% K−1 at 353K. As a consequence, this work indicates that Sr 3 P 4 O 13 : Eu2+/Eu3+ phosphors could be widely applied in optical temperature sensors. The Eu2+/Eu3+ co-doped Sr 3 P 4 O 13 thermometric phosphors is synthesized by solid-state reaction. the blue emission of Eu2+ ions and red emission of Eu3+ ions, can be used as fluorescence intensity ratio (FIR) signals. The dual-emissions has different thermal dependencies due to the competition between thermal-activated energy transfer and thermal quenching, thus enabling their intensity ratio to be highly sensitive to the temperature variation, which makes this phosphor a good candidate as ratiometric and colormetric temperature sensor. Image 1 • The emission of Eu2+ and Eu3+ ions can be observed Sr 3 P 4 O 13 : Eu2+/Eu3+ phosphors due to the self-reduction influence. • The blue emission of Eu2+ and red emission of Eu3+ ions can be used as fluorescence intensity ratio signals. • S a reached a maximum 0.008 K−1 at 573 K, while S r reached a maximum of 1.06% K−1 at 353K. [ABSTRACT FROM AUTHOR]

• Optical thermometry platform of Ti-Eu in flexible films and 3D micro-rod arrays. • Dual-mode thermometer shows outstanding reversibility and sensitivity. • Temperature/time-domains can serve as "key" to unlock the "locked" ciphertext. • Extended application for multi-dimensional high-level secure anti-counterfeiting. A novel thermometer, qualified with miniaturization, real-time monitoring, non-invasion, remote-control, and high spatio-temporal resolution, is urgently required for temperaturedetecting of sub-micrometric objects and in specific harsh conditions. Herein, we report an adaptable dual-mode optical thermometry platform LiTaO 3 :Ti4+, Eu3+@PDMS. A proof-of-concept implementation based on fluorescence thermometer (FT) demonstrates outstanding temperature sensing performance with excellent reversibility. The maximum S a and S r are as high as 0.671 and 5.425% K−1, respectively, with minimal temperature resolution of 0.14 K. Whilst, the maximum S a and S r based on lifetime thermometer (LT) are determined to be 0.122 and 3.637% K−1, respectively, with superior temperature resolution of 0.027–0.058 K. Finally, flexible phosphor films and 3D micro-rod arrays with handily encrypted information are fabricated for the unclonable multi-modal/multi-dimensional anti-counterfeiting application by exploiting light, temperature and time-domains as the "key" to decrypt the "locked" ciphertext, which indicates the promising prospect in temperature sensing and anti-counterfeiting. This work not only paves a way for developing novel spatial/temporal dual-mode real-time thermometer based on synergetic luminescence of lanthanide (Ln) and transition-metal (TM) ions with high temperature sensitivity and resolution, but also opens a new "window" for extending the thermometer as a flexible device in advanced multi-mode multi-dimensional high-level secure anti-counterfeiting. [ABSTRACT FROM AUTHOR]

Research on near-infrared (NIR) emission of Tm3+ and Yb3+ co-doped upconversion (UC) materials has accepted many interests owing to delightful features for frontier applications. In this work, we focus on the preparation of pure NIR emission and the improvement of absolute sensitivity (S A) on temperature in Tm3+ and Yb3+ co-doped novel double perovskite Gd 2 ZnTiO 6 (GZT) phosphors. Upon 980 nm excitation, these phosphors perform dramatical NIR emissions, and the integral intensity percentage of NIR emission versus total visible emissions reaches up to 99.88%. A high S A value with 1.7351 K−1 at 473 K for the I 801 /I 650 is obtained via introducing excellent NIR emission. Besides, the S A value of non-thermally coupled levels is higher than that of thermally coupled levels. These results suggest that this kind of UC material may be a candidate for NIR imaging and temperature detection applications. Image 1 High sensitivity based on non-thermally coupled levels is received via utilizing intense NIR emission in Tm3+ and Yb3+ co-doped double perovskite GZT phosphors. • Upconversion properties of Tm3+ and Yb3+ co-doped novel double perovskite Gd 2 ZnTiO 6 phosphors are investigated in detail. • Intense and nearly pure NIR emission with high integral intensity percentage that achieves 99.88% is obtained. • High S A with 1.7351 K−1 at 473 K for N-TCLs is received via utilizing intense near-infrared emission. [ABSTRACT FROM AUTHOR]

Modified organogels are bicontinuous colloidal systems which form a three‐dimensional network embedding well‐solvated organic dyes sensitive to minor changes in its microenvironment. It was demonstrated that these natural wax/oils based organogels can be applied for minimally invasive temperature sensing in life‐science objects. The desired temperature sensitivity of better than 100 mK, centered around the physiologically relevant temperature of 36 °C, is warranted by using the process of triplet‐triplet annihilation photon energy upconversion (TTA‐UC) as a sensing mechanism. This all‐optical sensing technique, based on ratiometric‐type signal registration, ensures significant independence of the data obtained on excitation intensity instabilities, local molecular concentration fluctuations and field‐of‐view variations. The TTA‐UC system is effectively protected for more than 1000 s against oxygen‐induced damage, allowing stable performance of this temperature‐sensing system even in ambient environments without lost of sensitivity and applying the same calibration curve. [ABSTRACT FROM AUTHOR]

In the present context, detailed spectroscopic analysis of Cr3+ doped ZnGa 2 O 4 has been reported. Hydrothermal method was adopted for the formation of nanoparticles. XRD patterns revealed the cubic phase with good crystallinity. The PL emission spectra showed a broadband NIR emission with a sharp peak from the 4T 2 and 2E states of Cr3+. Strong crystal field strength was estimated from the spectroscopic data for the Cr3+ ion in ZnGa 2 O 4 host. The material also showed long afterglow property. With increase of temperature, the FWHMs of the emission band were found to be increased and the average lifetimes were decreased because of the increasing population of the 4T 2 state. Further, the system was utilized for optical temperature sensing using lifetime based technique and maximum sensitivity was obtained as 0.018 K-1. UV, as well as blue and orange light was found to be suitable to be used as excitation sources for temperature sensing measurement. The possibility of the present nanophosphor to emit a long persistent signal in first biological window and the significant temperature dependent photoluminescence property allows it to be considered as a promising material in bioimaging application as well as for temperature sensing in biotechnological applications. • Urea assisted hydrothermal method was used to prepare the samples. • Cr3+ experience a strong crystal field in ZnGa 2 O 4 host. • With increase of temperature the FWHM of emission band increases but the PL peak intensity and lifetime decreases. • Lifetime based optical thermometry was done by exciting the sample at UV as well as blue and orange light. • The present nanophosphor is found to be a promising material for bioimaging and optical thermometry application. [ABSTRACT FROM AUTHOR]

We demonstrate a novel fiber Bragg grating (FBG) temperature sensor based on lead sulfide (PbS)-doped silica optical fiber, prepared by atomic layer deposition (ALD) doping technique. The FBGs are fabricated using the phase mask method, without hydrogen loading. The temperature sensitivity of the FBG-PbS is found to be $\sim$ 19 pm/ $^\circ$ C within 20–150 $^\circ$ C, showing great linearity and repeatability. It is increased by approximately 60% compared to the temperature sensitivity of FBG in standard single mode fiber (SMF). Furthermore, the temperature characteristics of PbS-doped silica optical fiber are investigated. The thermal expansion coefficient and thermal-optic coefficient of PbS-doped silica fiber are 6.3 $\times\; 10^{-7}$ and 1.23 $\times\; 10^{-5}$ / $^\circ$ C, respectively. Moreover, the thermal-optic coefficient value of the PbS-doped silica optical fiber is nearly one order of magnitude higher than that of SMF. Therefore, the FBG based on PbS-doped silica optical fiber appears to be very attractive for the temperature sensing fields. [ABSTRACT FROM AUTHOR]

In this paper, we present the results for thermal gradient measurements using constant period UV written long-period gratings (LPGs) in photosensitive and SMF-28 fibers. We have studied theoretically and experimentally the effect of thermal gradients on the spectrum of LPGs. It has been shown theoretically and confirmed experimentally that thermal gradients lead to changes of the depth of the grating spectrum while changes of the mean temperature cause shifts of the resonance wavelength. Thus, thermal gradients and average temperature can be independently measured using a single LPG. Sensitivities to temperature difference and to average temperature for LPGs in air have been found to be higher than in water. [ABSTRACT FROM AUTHOR]

How to improve the sensitivity of the temperature‐sensing luminescent materials is one of the most important objects currently. In this work, to obtain high sensitivity and learn the corresponding mechanism, the rare earth (RE) ions doped Y4.67Si3O13 (YS) phosphors were developed by solid‐state reaction. The phase purity, structure, morphology and luminescence characteristics were evaluated by XRD, TEM, emission spectra, etc. The change of the optical bandgaps between the host and RE‐doped phosphors was found, agreeing with the calculation results based on density‐functional theory. The temperature‐dependence of the upconversion (UC) luminescence revealed that a linear relationship exists between the fluorescence intensity ratio of Ho3+ and temperature. The theoretical resolution was evaluated. High absolute (0.083 K−1) and relative (3.53% K−1 at 293 K) sensitivities have been gained in the YS:1%Ho3+, 10%Yb3+. The effect of the Yb3+ doping concentration and pump power on the sensitivities was discussed. The pump‐power–dependence of the UC luminescence indicated the main mechanism for high sensitivities in the YS:1%Ho3+, 10%Yb3+. Moreover, the decay‐lifetime based temperature sensing was also evaluated. The above results imply that the present phosphors could be promising candidates for temperature sensors, and the proposed strategies are instructive in exploring other new temperature sensing luminescent materials. [ABSTRACT FROM AUTHOR]

A series of Ce3+ and Dy3+ doped LiY 9 (SiO 4) 6 O 2 phosphors was prepared by conventional high temperature solid state reaction method. The dominant emission of Dy3+ originates from the 4F 9/2 → 6H 13/2 (yellow emission) electric dipole transition while that of Ce3+ locates in the blue region. The concentration quenching for Dy3+ emission was investigated by luminescence spectra and decay curves, the main mechanism responsible for the energy transfer between Dy3+ ions was determined by the Inokuti-Hirayama model. Energy transfer from Ce3+ to Dy3+ as well as the temperature sensing property was studied in detail. Thanks to the different thermal responses between Ce3+ and Dy3+ in the host, the highest sensing sensitivity was calculated to be 0.43% K−1. The results demonstrate that LiY 9 (SiO 4) 6 O 2 : Ce3+, Dy3+ may be a potential candidate for a luminescent ratiometric thermometer. [ABSTRACT FROM AUTHOR]

In this study, we report the synthesis and some new crystal structures of tetrakis lanthanide β-diketonate complexes throughout the lanthanide series for homonuclear (Pr3+, Nd3+, Sm3+, Eu3+, Tb3+, Dy3+, Er3+ and Yb3+) as well as for heteronuclear (Eu3+-Tb3+ and Tb3+-Sm3+) complexes. The well-known 1,1,1-trifluoro-2,4-pentadione (Htfac) ligand has been used in the synthesis. Here, we show that when employing the same synthesis conditions, we can obtain complexes with different coordination environments of the lanthanide ions. This is strongly linked to the ionic radius of the lanthanide ion. The luminescence properties of the visible emitting complexes (Ln3+ = Eu3+, Tb3+, Sm3+ and Dy3+) were investigated in solution as well as solid state. The near-infrared emitting complexes (Ln3+ = Pr3+, Nd3+, Er3+ and Yb3+) were recorded in the solid state. The heteronuclear complexes ([Eu 1-x Tb x (tfac) 8 ]2-Na 2 + (x: 0.59 (1) and 0.47 (2), Tb 1-y Sm y (tfac) 8 ]2-Na 2 + (y: 0.1 (3) and 0.2 (4)) and homonuclear complex [Dy(tfac) 4)]−Na+ (DyL 4) exhibited temperature-dependent luminescence properties in the physiological range, with complex DyL 4 showing the highest relative sensitivity S r = 3.45% K−1 (280 K). Complex 2 also showed a high S r = 2.70% K−1 (353 K), which makes them promising for application as physiological luminescence thermometers. To the best of our knowledge until now no lanthanide β-diketonate complexes have been reported for use as good luminescence thermometers operating in the physiological range. Tetrakis β-diketonate lanthanide complexes shows temperature-dependent luminescence in physiological temperature range. Image 1 [ABSTRACT FROM AUTHOR]

Temperature detection based on the fluorescence intensity ratio (FIR) has been considered to be a promising technique for non-contact temperature measurement. Unfortunately, the FIR-based temperature sensor materials generally show low temperature sensitivity because of the narrow energy gap between the thermally coupled energy levels. In this work, lanthanide-doped Ba 3 Y 4 O 9 (BYO) upconversion luminescent materials were synthesized in order to explore their potential application in optical thermometer. The crystal structure of the present samples was investigated by XRD and further refined by the Rietveld method, which indicate that the dopant ions successfully enter the host lattice by occupying Y3+ sites. Excited by 980 nm, BYO:Ho3+/Yb3+ and BYO:Tm3+/Yb3+ present high-purity green and blue output colors, respectively. Based on the analysis of emission intensity ratio and pump-power dependence, the upconversion emission mechanisms are systematically investigated. Subsequently, the temperature sensing performances of BYO:Ho3+/Yb3+ and BYO:Tm3+/Yb3+ based on FIR technique are evaluated in the temperature range of 298–573 K under 980 nm excitation. Owing to the different temperature-dependent behaviors of different emission bands and larger energy gaps, the present materials display high sensitivity, good repeatability and excellent stability. The maximum absolute sensitivity of BYO:Ho3+/Yb3+ and BYO:Tm3+/Yb3+ reach as high as 79.62 × 10−4 K−1 and 193.51 × 10−4 K−1, respectively. Among them, the highest sensitivity of BYO:Tm3+/Yb3+ is far higher than those of other optical temperature sensors using the thermally coupled levels based on FIR technique. The results indicate that the present materials are promising for application as optical thermometer in non-contact temperature detection, and using FIR of 5F 1 /5G 6 and 5F 2,3 /3K 8 multiplets (Ho3+), and 3F 2,3 /1G 4 (Tm3+) are feasible methods for accurate temperature detection. [ABSTRACT FROM AUTHOR]

In this paper, an optical thermometry strategy based on dual emission centers involving rare earth ions and self-activated host luminescence has been proposed, which can be used to design self-referencing optical thermometer with high temperature sensitivity and signal discriminability. Herein, we prepared non-rare-earth self-activated and rare-earth activated LiCa 3 MgV 3 O 12 (LCMV) phosphors by a conventional high-temperature solid-state reaction method. Their structure, luminescence as well as temperature sensing property have been systematically investigated. In this sample, the emissions of Eu3+ ions and [VO 4 ]3− group have been simultaneously monitored under 335 nm UV light excitation. The FIR of Eu3+ to [VO 4 ]3- shows great temperature sensing property in temperature range from 303 K–523 K,owing to the energy transfer and thermal quenching behavior. The measured maximum absolute and relative temperature sensitivity of this phosphor are 0.011 K−1 and 1.689%K−1, which is remarkably higher than most of luminescent materials reported previously. Meanwhile, the emission peaks of [VO 4 ]3- (475 nm) and Eu3+ (610 nm) provide a good signal discriminability for temperature detection. What's more, the emitting color in the temperature-dependent CIE diagram can highly be influenced by the external temperature and the color coordinate is verified from (0.257, 0.332) to (0.503, 0.342), which can be fitted well with the linear equation. All results indicate that the obtained phosphors not only can be promising materials for optical temperature sensors, but can be used as a color-temperature indicator. [ABSTRACT FROM AUTHOR]

The strategies of introducing interior defects and reducing mean particle size have been applied to improve negative thermal quenching effect (TQE) in Yb 3 + sensitized fluoride upconversion (UC) nanocrystals (NCs) recently. Herein, an active-core/active-shell structure with high total Yb 3 + doping content is used to enhance the absorption intensity of Er 3 + ions. Moreover, the Er 3 + activators are doped into the shell to enable the energy migration process from activators to surface defects. In this scenario, with the rise of temperature, the suppression degree of this energy migration process is enlarged followed by an improved negative TQE. Specifically, with rising the temperature from 293 K to 413 K, the integral upconversion emission intensity of 40Yb: NaGdF 4 @60Yb/2Er: NaGdF 4 NCs increases by ∼ 8.24 times, while that of NaGdF 4 @20Yb/2Er: NaGdF 4 NCs with a similar mean particle size only enhances ∼ 3.44 times. • Yb: NaGdF 4 @Yb/Er: NaGdF 4 NCs with an active-core/active-shell structure is prepared. • This architecture enables the energy migration process from activators to surface defects. • This architecture with high Yb3＋ content enhances the absorption intensity of Er3＋ ions. • This architecture enhances negative thermal quenching effect evidently. [ABSTRACT FROM AUTHOR]

Tellurite glasses of TeO 2 BaF 2 −REF 3 (RE = La, Gd, and Y) co-doped with Er3+/Yb3+ were prepared and investigated comparatively for optical fiber temperature sensors. For this purpose, their thermal and optical properties were examined in detail. The J-O theory was adopted to estimate the transition properties based on absorption spectra. The dominant green emissions were observed in both of the downshifting and upconversion luminescence. The optical temperature sensing abilities based on the FIR of Er3+ green emissions were studied under both of the UV (380 nm) and NIR (980 nm) excitations. Results show that these three tellurite glasses, especially for the TBG glass, should be very qualified for the design of optical fiber temperature sensors under different excitation modes. [ABSTRACT FROM AUTHOR]

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A dual parameter optical fiber sensor for temperature and pressure discrimination has been proposed and experimentally realized. A tapered fiber Bragg grating (tapered-FBG) and an extrinsic Fabry–Perot interferometer with a ball shape (ball-EFPI) are the two main sensing structures. The taper is fabricated by elongating it during an arc-discharge provided by the fusion splicer. Then, the femtosecond laser is used to inscribe a first-order Bragg grating in the taper region, adopting the point-by-point direct-writing technique. The ball-EFPI is fabricated using the chemical etching and arc-discharge enlargement method. The test temperature range is 40 °–400°, and the test pressure range is 0–2 MPa on the basis of ambient pressure. Experimental results show that the tapered-FBG has good temperature response while the ball-EFPI is sensitive to pressure. By analyzing the sensitivity matrix, the temperature and pressure discrimination can be achieved using the proposed hybrid sensor. [ABSTRACT FROM AUTHOR]

Highlights • Different strategies for temperature sensing were introduced in the present phosphors. • High sensor sensitivity has been obtained in the present phosphors. • The developed phosphors could have potential application in optical temperature sensors. Abstract In order to develop new upconversion (UC) phosphors for optical temperature sensors, a series of Yb3+-Tm3+-Tb3+/Eu3+ doped Ca 2 Gd 8 (SiO 4) 6 O 2 (CGS) samples were designed by solid-state reaction method. The phase purity was examined by XRD patterns, which revealed that the obtained samples are all single-phase in spite of the rare earth (RE) ions doping. Upon 980 nm excitation, the emission peaks of all the doped luminescent ions (Tm3+, Tb3+ and Eu3+) have been observed, and the energy transfer processes among the RE ions in the UC luminescence were discussed with the help of the energy level diagram and decay curves. The competitive absorption between Tm3+ and Tb3+/Eu3+ from Yb3+ was proposed to interpret the sharp decrease of Tm3+ emission intensity. The temperature sensing behavior was evaluated by measuring the temperature-dependent UC luminescence of the typical CGS:10%Yb3+,0.2%Tm3+,10%Tb3+,1.25%Eu3+ phosphor. It has been found that the fluorescence intensity ratio (FIR) technique by employing I Tb /I Eu and I Tb /I Tm can generate high absolute sensitivity, but the relative sensitivity still needs further improvement compared with some other phosphors doped with Er3+/Ho3+/Tm3+. [ABSTRACT FROM AUTHOR]

Energy transfer (ET) and cross-relaxation (CR) processes play significant roles in regulating emitting colors and intensity of upconversion (UC) materials. Calculating the coefficients in ET and CR processes can provide visual descriptions for evaluating the UC luminescence properties. Here, we find that those ET and CR processes are responsible for the color-tunable properties in Gd 2 Ce 2 O 7 : Yb3+, Er3+ phosphors. By solving the rate equation, mathematical expressions are established to calculate the ET and CR coefficients based on the experimental UC spectra and lifetimes. The results are benefit to evaluate the efficiencies of ET and CR processes in quantization in different Yb3+ ion concentrations doped samples. The coefficients of ET process arise from 1.05 to 7.93 × 1017 cm3s−1 while those of CR process increase from 2.69 to 72.01 × 1017 cm3s−1 with increasing the Yb3+ ion concentration, which suggest that the CR and ET processes are efficient in Gd 2 Ce 2 O 7 host. Furthermore, potential temperature sensing properties are also evaluated according to the fluorescence intensity ratio of 2H 11/2 and 4S 3/2 levels and the maximal sensitivity (S) is achieved about 0.00337 K−1 at 503 K. This work provides an insight into the evaluation of those UC processes and reveals the capacity in color-tunable and temperature sensing aspects. [ABSTRACT FROM AUTHOR]