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Recently high doping of lanthanide ions (till 100 %) is realized unprecedentedly in nanostructured upconversion (UC) phosphors. However, oddly enough, this significant breakthrough did not result in a corresponding UC enhancement at ambient temperature, which hinders the otherwise very interesting applications of these materials in various fields. In this work, taking the Er3+‐rich UC nanosystem as an example, we confirm unambiguously that the phonon‐assisted cross relaxation (CR) is the culprit. More importantly, combining the theoretical modeling and experiments, the precise roles of different CR channels on UC energy loss are quantitatively revealed. As a result, lowering the temperature can exponentially enhance the relevant UC luminescence by more than two orders of magnitude. Our comprehension will play an important role in promoting the UC performance and further application of high doping rare earth materials. As a proof of concept, an Er3+‐rich core/multi‐shell nanophosphor is exploited which demonstrates the great potential of our finding in the field of ultra‐sensitive temperature sensing. [ABSTRACT FROM AUTHOR]

Transparent glass ceramic with Ba 2 NaNb 5 O 15 as the main crystal phase was prepared, and the appropriate heat treatment condition was selected as 710 °C/150 min through various characterizations. The luminous intensity and thermal stability were enhanced significantly when the glass ceramic was used as the luminous matrix. After introducing Ti4+ ions as charge compensators, the luminescence performance and thermal stability were further improved, and the reasons for this were analyzed. At 458 K, the luminous intensity of 0.5%Eu3+ doped glass ceramic containing 0.5%Ti4+ can maintain about 65% of room temperature with a chromaticity shift of 5.16 × 10−2. The relative and absolute sensitivities of 0.7%Er3+ doped glass ceramic were 4.04 × 10−3 K−1 and 1.31% K−1. Introducing Ti4+ ions would weaken the population redistribution ability of 2H 11/2 and 4S 3/2 levels and reduce the temperature sensitivity. However, the sample containing Ti4+ shows good thermal stability, its green emission at 458 K has a small chromaticity shift of 6.45 × 10−3. The research shows that the glass ceramic can be used as a good luminescent host material, and Eu3+/Er3+ doped glass ceramic can be used in the fields of LEDs or temperature sensing. [ABSTRACT FROM AUTHOR]

We have fabricated CsPb(Cl/Br) 3 quantum dots (QDs) and Tb3+ co-doping glass and comparatively investigated four-mode temperature sensing of fluorescence intensity ratio (FIR), full width at half maximum (FWHM), lifetime and chromatic coordinate. Temperature dependent photoluminescence (PL) spectra are measured. The Tb3+ ions and CsPb(Cl/Br) 3 QDs have independent luminescence and FIR of Tb3+ to QDs has obvious decrease with temperature, which is used for FIR temperature sensing. The PL and PL decay of QDs are used for FWHM and lifetime temperature sensing. The change of FIR with temperature leads to the change of luminous color and chromatic coordinate with temperature. A new chromatic temperature sensing method is established, which utilizes linear relation of chromatic coordinate and temperature. Temperature dependence for FIR, FWHM, lifetime and chromatic coordinate has been fitted. Absolute sensitivity, relative sensitivity, temperature accuracy and repeatability have been evaluated. Among the four sensing modes, the FIR and chromatic coordinate modes have large sensitivity and small accuracy. The FIR mode is better than chromatic coordinate mode in absolute sensitivity and relative sensitivity, whereas the chromatic coordinate mode is better in its good linear relation. The four sensing modes have excellent repeatability due to the stability of QDs-Tb3+ co-doping glass. [ABSTRACT FROM AUTHOR]

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Pr-doped metal oxide polycrystalline transparent ceramics are highly desirable for photothermal window systems served in extreme environments; however, obtaining efficient photoluminescence (PL) together with high transparency in these ceramics is still posing serious challenges, which undoubtedly limits their applications. Here, Pr-doped Y2Zr2O7 (YZO) transparent ceramics, as an illustrative example, are prepared by a solid-state reaction and vacuum sintering method. Owing to the elimination of defect clusters [PrY4+−O2−−PrY4+] and [PrY4+−e′] without the introduction of impurities and additional defects, the fabricated YZO:Pr ceramics exhibit high transparency (74%) and efficient PL (39-fold enhanced) after air annealing plus vacuum re-annealing treatment. Moreover, upon 295/450 nm excitation, the emission bands (blue, green, red, and dark red) from YZO:Pr ceramics present different temperature-dependent properties due to the thermal-quenching channel generated by the intervalence charge transfer (IVCT) state between Pr3+ and Zr4+ ions. Furthermore, a self-calibrated temperature feedback window with the same fluorescence intensity ratio (FIR) model (I613/I503, where I represents the intensity) under different excitation light sources (295 and 450 nm) is designed. The developed photothermal window operated in a wide temperature range (303–663 K) shows relatively high sensitivities (absolute sensitivity (Sa) and relative sensitivity (Sr) reach 0.008 K−1 at 663 K and 0.47% K−1 at 363 K, respectively), high repeatability (> 98%), and low temperature uncertainty (δT < 3.2 K). This work presents a paradigm for achieving enhanced PL along with elevated transparency of lanthanide (Ln)-doped ceramics through vacuum re-annealing treatment engineering and demonstrates their promising potential for photothermal window systems.

In this work, we demonstrate the usability of a fully-2D-material based device consisting of MoS2/WSe2 heterojunction encapsulated by hBN and contacted by graphene as temperature sensor for linear temperature measurement at cryogenic temperatures. More precisely, temperatures in the range of 10 K up to 300 K were applied to the device while recording the I-V characteristics. In contrast to the classical expectation, the main current flows through the device when it is reversely biased. We ascribe this to a combination of drift-diffusion and band-to-band tunneling, while for very low temperatures (T $ < $ 100 K), variable-range hopping or trap-assisted tunneling seems dominant. In case of forward bias, the Schottky contact on the WSe2-anode hinders the charge transport in the voltage range of interest. Additionally, we obtained the activation energy of the saturation current in reverse direction in an Arrhenius diagram. Depending on the bias level, it varies between 100 meV and 300 meV, which may be related to the energy barrier caused by interface traps, generation centers between both semiconducting 2D materials, and the band-to-band tunneling. Furthermore, we investigated the temperature-sensor performance by applying a constant current to the device and measuring the voltage drop at different temperatures. In the range of 40 K up to 300 K, the sensitivity of the sensor is $\sim 2$ mV/K, which is comparable to Si devices, while the linearity is still lower $(R^{2}~\sim ~0.94$ ). On the other hand, the demonstrated device consists only of 2D materials and is, thus, substrate independent, very thin, and can potentially be fabricated on a fully flexible substrate in a low-cost process.

A sensitive temperature sensor was demonstrated using boron-doped polarization-maintaining photonic crystal fiber (PM-PCF) as a Sagnac interferometer (SI). This boron-doped PM-PCF combines both the geometric birefringence introduced by the PCF structure design and the stress birefringence introduced by the boron-doped stress-applying parts. However, we found that the stress birefringence dominates the total birefringence of the sensor by numerical analysis. In the experiments, the fabricated sensor exhibited the highest temperature sensitivity of −1.83 nm/°C within the wide temperature range of 28~76 °C. The temperature sensitivity was mainly derived from the stress birefringence of boron-doped PM-PCF SI. These findings provide some support for the designation of high-precision temperature sensors.

Simultaneous photothermal ablation of multiple tumors is limited by unpredictable photo‐induced apoptosis, caused by individual intratumoral differences. Here, a multi‐channel lanthanide nanocomposite was used to achieve tailored synergistic treatment of multiple subcutaneous orthotopic tumors under non‐uniform whole‐body infrared irradiation prescription. The nanocomposite reduces intratumoral glutathione by simultaneously activating the fluorescence and photothermal channels. The fluorescence provides individual information on different tumors, allowing customized prescriptions to be made. This enables optimal induction of hyperthermia and dosage of chemo drugs, to ensure treatment efficacy, while avoiding overtherapy. With an accessional therapeutic laser system, customized synergistic treatment of subcutaneous orthotopic cancer cases with multiple tumors is possible with both high efficacy and minimized side effects. [ABSTRACT FROM AUTHOR]

Metal-organic frameworks are of great interest to scientists from various fields. This group also includes organic–inorganic hybrids with a perovskite structure. Recently their structural, phonon, and luminescent properties have been paid much attention. However, a new way of characterization of these materials has become luminescence thermometry. Herein, we report the structure, luminescence, and temperature detection ability of formate organic–inorganic perovskite [C(NH2)3]M(HCOO)3 (Mg2+, Mn2+, Zn2+) doped with Cr3+ ions. Crystal field strength (Dq/B) and Racah parameters were determined based on diffuse reflectance spectra. It was shown that Cr3+ ions are positioned in the intermediate crystal field or close to it with a Dq/B range of 2.29–2.41. The co-existence of the spin-forbidden and spin-allowed transitions of Cr3+ ions enable the proposal of an approach for remote readout of the temperature. The relative sensitivity (Sr) can be easily modified by sample composition and Cr3+ ions concentration. The luminescent thermometer based on the 2E/4T2g transitions has the relative sensitivity Sr of 2.08%K−1 at 90 K for [C(NH2)3]Mg(HCOO)3: 1% Cr3+ and decrease to 1.20%K−1 at 100 K and 1.08%K−1 at 90 K for Mn2+ and Zn2+ analogs, respectively. [ABSTRACT FROM AUTHOR]

A novel fluorescent probe (C460@Tb-MOFs) was designed and synthesized by encapsulating the fluorescent dye 7-diethylamino-4-methyl coumarin (C460) into a terbium-based metal–organic framework using a simple ultrasonic impregnation method. It is impressive that this dye-modified metal–organic framework can specifically detect styrene and temperature upon luminescence quenching. The sensing platform of this material exhibits great selectivity, fast response, and good cyclability toward styrene detection. It is worth mentioning that the sensing process undergoes a distinct color change from blue to colorless, providing conditions for the accurate visual detection of styrene liquid and gas. The significant fluorescence quenching mechanism of styrene toward C460@Tb-MOFs is explored in detail. Moreover, the dye-modified metal–organic framework can also achieve temperature sensing from 298 to 498 K with high relative sensitivity at 498 K. The preparation of functionalized MOF composites with fluorescent dyes provides an effective strategy for the construction of sensors for multifunctional applications. [ABSTRACT FROM AUTHOR]

[Display omitted] • Emission tailorable UCNPs are constructed for dynamic anti-counterfeiting and temperature sensing. • The thermal, excitation wavelength and power triple-mode responsive multicolor emission is achieved in a single matrix • The emission of NaYbF4 shelled UCNPs always shows temperature-dependent increases regardless of the conditions. Lanthanide (Ln3+) luminescent materials play a crucial role in information security and data storage owing to their excellent and unique optical properties. The advances in dynamic colorful luminescent anti-counterfeiting nanomaterials enable the generation of a high-level information encryption. In this work, a superior thermal, optical wavelength and excitation power triple-mode stimuli-responsive emission color modulation is demonstrated in a lanthanide-doped nanostructured luminescent material. The plentiful emission colors are manipulated by modulating the composition of a fluoride core–shell nanostructure with different Ln3+ at different doping concentrations. The nanomaterials display remarkable excitation wavelength/power-dependent color change, along with temperature-dependent color variation in the range from 298 K to 437 K, with a good relative sensitivity S r of 1.1387% K−1 at 398 K. The universal optical modulation, combined with the excellent optical and structural stability of the luminescent nanoparticles, renders many advantages for the anti-counterfeiting application. This work explores a universal strategy for the manipulation of triple-mode stimuli-responsive dynamic luminescence and demonstrates its good potential for anti-counterfeiting application. [ABSTRACT FROM AUTHOR]

Rare earth ions doped upconversion materials have an extensive range of utilizations because of their exceptional luminescence properties. Here, scheelite type Yb3+, Er3+ co-doped KBi(MoO 4) 2 nanomaterials were produced by means of a conventional co-precipitation method at room temperature with a typical crystallite size of 13 nm. 980 nm excitation aided in the investigation of the concentration and power-dependent upconversion emission. The optimum upconversion emission is obtained with Er and Yb concentrations of 0.035 and 0.125 mol%, respectively in KBi(MoO 4) 2 nanomaterials. The intensity ratio of upconversion emission bands based on 529 and 551 nm is investigated in the temperature range of 200–550 K and the theoretical function is used for fitting the exploratory information. The absolute sensitivity is found to be of maximum value of 0.0123 K-1, indicating that this double molybdate can be utilized as a potential probe for luminescence-based temperature sensing. [ABSTRACT FROM AUTHOR]

In this research, a thermally activated upconversion luminescence (UCL) probe with ratiometric temperature sensing under 1064 nm and 808 nm excitation was designed. Especially, Nd3+, Tm3+ and Ce3+ were doped in rare earth nanoparticles (RENPs) as UCL modulators. By optimizing the elements and ratios, the excitation wavelength is successfully modulated to 1064 nm excitation with UCL intensity enhanced. Additionally, the prepared RENPs have a significant temperature response at 1064 nm excitation and can be used for thermochromic coatings. The intensity ratio of three-photon UCL (1064 nm excitation) to two-photon UCL (808 nm excitation) as an exponential function of temperature can be used as a ratiometric temperature detector. Therefore, this designed thermochromic coatings may enable new applications in optoelectronic device and industrial sensor. [ABSTRACT FROM AUTHOR]

A multifunctional double‐perovskite‐type Ca2LnSbO6 (Ln = La, Y, Gd, and Lu) phosphors with Eu3+ and Mn4+ co‐doped were successfully synthesized and designed to simultaneously apply to temperature sensing and plant growth LED. With temperature varying from 303 to 523 K, the integrated intensity of Mn4+ ions (2Eg → 4A2g) markedly decline swifter comparing to Eu3+ ions (5D0 → 7F2) due to the thermal quenching effect. It implies that Mn4+ is susceptive to the temperature in this work. Eu3+ exhibits high heat resistance, which can be selected as a calibration parameter for the fluorescence intensity ratio temperature sensor. The maximum relative sensitivity (Sr) values of Ca2LnSbO6:1%Eu3+, 0.5%Mn4+ (Ln = La, Y, and Gd) phosphor are estimated as 2.19% K−1 at 443 K, 1.68% K−1 at 503 K, and 1.80% K−1 at 483 K, respectively. They are superior to many recent emerging phosphors. Moreover, upon 365 nm excitation, Ca2LnSbO6:1%Eu, 0.5%Mn (Ln = La, Y, Gd, and Lu) phosphors display a wide red emission peaking at 696, 680, 677, and 684 nm, respectively. They come from the overlapped of 2Eg–4A2g of Mn4+ and 5D0–7F4 transition of Eu3+. Their full widths at half maximum are 34, 35, 35, and 29 nm, respectively. They are all perfectly overlapping the absorption curves of chlorophyll a and chlorophyll b, and their fabricated red phosphor‐converted light‐emitting diode device ulteriorly corroborated the promising applications for plant growth. Markedly, the systematic analysis of their crystal chemistry and site preferentially occupancy is first reported and discussed by the bond valence theory. [ABSTRACT FROM AUTHOR]

In this work, a method for controllable regulation of crystal form was proposed for the first time and the effects of different crystal forms on the up‐conversion luminescence properties of Ho3+, Yb3+ co‐doped K3Sc0.5Lu0.5F6 (KSLF) phosphors was explored. KSLF:Ho3+, Yb3+ phosphors were synthesized by the high temperature solid‐state reaction method, and X‐ray diffraction (XRD) results illustrate that the compounds can obtain monoclinic phase and cubic phase at different synthesis temperatures. In addition, according to the power‐dependent up‐conversion luminescence (UCL) intensity, the UCL mechanism and the electronic transition process are discussed. Simultaneously, the temperature sensing behavior of the best samples with different crystal forms at different temperatures was studied by fluorescence intensity ratio technique. All the results show that KSLF:Ho3+, Yb3+ phosphors show great application potential in the field of temperature sensing, and the preparation of KSLF:Ho3+, Yb3+ in different crystal forms can provide a reference value for crystal design and growth. [ABSTRACT FROM AUTHOR]

As one of the most critical parameters to evaluate the quality and performance of mobile phones, real-time temperature monitoring of mobile phones' integrated chips is vital in the electronics industry. Although several different strategies for the measurement of chips' surface temperature have been proposed in recent years, distributed temperature monitoring with high spatial resolution is still a hot issue with an urgent need to be solved. In this work, a fluorescent film material with photothermal properties containing thermosensitive upconversion nanoparticles (UCNPs) and polydimethylsiloxane (PDMS) is fabricated for the monitoring of the chips' surface temperature. The presented fluorescent films have thicknesses ranging from 23 to 90 μm and are both flexible and elastic. Using the fluorescence intensity ratio (FIR) technique, the temperature-sensing properties of these fluorescent films are investigated. The maximum sensitivity of the fluorescent film was measured to be 1.43% K−1 at 299 K. By testing the temperature at different positions of the optical film, distributed temperature monitoring with a high spatial resolution down to 10 μm on the chip surface was successfully achieved. It is worth mentioning that the film maintained stable performance even under pull stretching up to 100%. The correctness of the method is verified by taking infrared images of the chip surface with an infrared camera. These results demonstrate that the as-prepared optical film is a promising anti-deformation material for monitoring temperature with high spatial resolution on-chip surfaces. [ABSTRACT FROM AUTHOR]

Researches on fluorescence intensity ratio (FIR) based temperature sensors have become more and more popular in recent years. Herein, we co-doped Pb2+ and Sm3+ into the host material Ba 2 MgY 2 (BO 3) 4 (BMYB) to prepare a new series of phosphors. The Pb2+ activated phosphor BMYB:0.03 Pb2+ presents a wide blue emission band centered at 416 nm under 278 nm laser excitation with internal quantum efficiency of 46%. In the presence of both Pb2+ and Sm3+, energy transfer will occur between them, resulting in tunable color emission. Besides, the phosphor has an absolute sensitivity of 0.96% K−1 at 575 K, which makes it an excellent candidate for temperature sensing. These findings suggest that prepared phosphor is a potential candidate for color tunable phosphor and temperature sensing material. [ABSTRACT FROM AUTHOR]

Increasing demand for fire safety has aroused the enthusiasm of researchers for exploring early-stage fire-warning materials. Herein, an early-stage fire-warning cotton fabric (denoted as CF-CP-FR) was designed with a two-layered structure: conducting polymer layer and flame-retardant layer, through in-situ chemical oxidation polymerization of polypyrrole (PPy) and dip coating of the compound of montmorillonite and ammonium polyphosphate (MMT@APP), respectively. Based on the thermoelectric effect of the PPy, CF-CP-FR was endowed with accurate temperature sensing capability below 100 °C. When encountering fire, CF-CP-FR showed excellent fire-warning response as fast as 1.0 s and displayed repeatable fire-warning capability under the protection of the MMT@APP. Via the mechanism of thermo-induced resistance change, the coated cotton fabric could also trigger the fire warning circuit at ca. 2.0 s. Meanwhile, the flame retardancy and thermal stability of CF-CP-FR were significantly enhanced, owing to the synergetic effect of MMT and APP. This work is promising in fabricating multifunctional clothing with efficient fire safety and smart fire-warning capability. [ABSTRACT FROM AUTHOR]

Lanthanide‐doped halide perovskite has emerged as a promising phosphor for multimode luminescence. Here, a chloride‐based perovskite single crystal is reported, namely Cs2NaInCl6:Yb3+,Er3+, that is grown in a hydrothermal reactor. The as‐grown crystals feature two distinct luminescence behaviors under UV and 980 nm laser excitation, respectively. Under UV lamp excitation, the crystal shows a multicolor emission of sharp bands at 448, 550, and 660 nm, covering a wide color gamut in CIE diagram. In stark contrast, the crystal under 980 nm excitation exhibits a pure green upconversion with a green‐to‐red ratio up to 211. The universal green dominance is further demonstrated in many chlorides, including Cs2AgInCl6, Cs2NaBiCl6, and Cs2AgBiCl6. The strong green upconversion is used for optical thermometry, which demonstrates an unprecedented sensitivity up to 9.3% K−1 at the low temperature end. The work introduces a kind of new hosts for single‐band upconversion luminescence, opening up many possibilities in areas such as low‐threshold laser and pure‐green color converter. [ABSTRACT FROM AUTHOR]

A zincate material, BaLa 2 ZnO 5 was successfully synthesized by a high-temperature solid-state method as a host for Bi3+. All the peaks in the X-ray diffraction patterns of the obtained material could be attributed to single phase BaLa 2 ZnO 5. The BaLa 2 ZnO 5 host exhibited strong band-to-band absorption in the range of 200–290 nm. After the doping of Bi3+, the absorption band due to band-to-band transition decreased, and three new absorption bands appeared. Upon monitoring the luminescence of Bi3+ at 407 nm, three excitation peaks were observed for BaLa 2 ZnO 5 : Bi3+, which could be attributed to A, C and metal-to-metal charge-transfer states by analyzing its excitation and absorption spectra. When codoped with Bi3+ and Sm3+, BaLa 2 ZnO 5 : Bi3+/Sm3+ exhibited strong energy transfer process from Bi3+ to Sm3+. Variable-temperature emission spectra revealed that the luminescence intensity of Bi3+ decreases rapidly with the increase in temperature, while that of Sm3+ ions decreases slowly. The relative sensitivity (S R) values of the BaLa 2 ZnO 5 : Bi3+ and BaLa 2 ZnO 5 : Bi3+/Sm3+ phosphors to temperature (1.77 and 1.12% K−1, respectively) were high and extremely stable in the range of 293–423 K. Therefore, the Bi3+-doped BaLa 2 ZnO 5 phosphor has great application potential for biological temperature sensing. [ABSTRACT FROM AUTHOR]

A simple temperature sensor based on ZnO composite graphene is demonstrated. With the temperature changes, the electron mobility of ZnO composite graphene changes accordingly, which leads to an effective change in the refractive index of ZnO composite graphene. Experimental results show that micro‐nano fiber coated with spherical ZnO composite graphene exhibits a higher sensitivity of 0.018 dB/°C in the temperature range of 25–60°C. Overall, the results verify the effectiveness of the proposed temperature sensor in accurate temperature measurement and offer a new, unique, and convenient direction for temperature sensing. [ABSTRACT FROM AUTHOR]

For biological embryo incubation, it is very important to monitor temperature accurately, so a new Mach–Zder interference (MZI) fiber temperature sensor is based on a microfiber coupler (MFC). It consists of a 3 dB fiber coupler and MFC forming an MZI structure. Since the MFC has strong evanescent field properties, higher sensitivity can be generated when fully acting with the external temperature environment. The experimental results show that the optical fiber sensor has good temperature response properties in the temperature range of 24–38°C, and the temperature sensitivity increases rapidly as the MFC waist diameter decreases. The maximum wavelength sensitivity of approximately 191.93 pm/°C and R2 = 0.98739, with the advantages of high sensitivity, simple manufacturing, and low cost can be applied in the field of bioincubation temperature monitoring. [ABSTRACT FROM AUTHOR]

Optical ring resonators (RRs) are a novel sensing device that has recently been developed for several sensing applications. In this review, RR structures based on three widely explored platforms, namely silicon-on-insulator (SOI), polymers, and plasmonics, are reviewed. The adaptability of these platforms allows for compatibility with different fabrication processes and integration with other photonic components, providing flexibility in designing and implementing various photonic devices and systems. Optical RRs are typically small, making them suitable for integration into compact photonic circuits. Their compactness allows for high device density and integration with other optical components, enabling complex and multifunctional photonic systems. RR devices realized on the plasmonic platform are highly attractive, as they offer extremely high sensitivity and a small footprint. However, the biggest challenge to overcome is the high fabrication demand related to such nanoscale devices, which limits their commercialization. [ABSTRACT FROM AUTHOR]

As one of the promising human—machine interfaces, wearable sensors play an important role in modern society, which advances the development of wearable fields, especially in the promising applications of electronic skin (e-skin), robotics, prosthetics, and healthcare. In the last decades, wearable sensors tend to be capable of attractive capabilities such as miniaturization, multifunction, and smart integration, and wearable properties such as lightweight, flexibility, stretchability, and conformability for wider applications. In this work, we developed a stretchable multifunctional sensor based on porous silver nanowire/silicone rubber conductive film (P-AgNW/SR). Its unique structural configuration, i.e., an assembly of the P-AgNW/SR with good conductivity, stability, and resistance response, and the insulated silicone rubber layer, provided the feasibility for realizing multiple sensing capabilities. Specifically, porous microstructures of the P-AgNW/SR made the device to be used for pressure sensing, exhibiting outstanding dynamic and static resistive responsive behaviors and having a maximum sensitivity of 9.062 %·N−1 in a continuous compressive force range of ∼ 16 N. With the merit of the good piezoresistive property of AgNW/SR networks embedded into the surface of micropores of the P-AgNW/SR, the device was verified to be a temperature sensor for detecting temperature changes in the human body and environment. The temperature sensor had good sensitivity of 0.844 %·°C−1, high linearity of 0.999 in the range of 25–125 °C, and remarkable dynamic stability. Besides, the developed sensor was demonstrated to be a single electrode-triboelectric sensor for active sensing, owing to the unique assembly of the conductive P-AgNW/SR electrode and the silicone rubber friction layer. Based on the coupling effect of the triboelectrification and electrostatic induction, the generated electrical signals could be used to sense the human motions, according to the quantitative correlation between the human motions and the features in amplitude and waveform of the output signals. Thus, the developed stretchable sensor successfully achieved the integration of two types of passive sensing capabilities, i.e., pressure and temperature sensing, and one type of active sensing capability, i.e., triboelectric sensing, demonstrating the feasibility of monitoring multiple variables of the human body and environment. [ABSTRACT FROM AUTHOR]

In this paper, a temperature sensing scheme with a miniature MZI structure based on the principle of inter-mode interference is proposed. The sensing structure mainly comprises single mode–coreless–multimode–coreless–single mode fibers (SCMCSs), which have been welded together, with different core diameters. The light beam has been expanded after passing through the coreless optical fiber and is then coupled into a multimode optical fiber. Due to the light passing through the cladding and core mode of the multimode optical fiber with different optical paths, a Mach–Zehnder interferometer is formed. Moreover, due to the thermo-optic and thermal expansion effects of optical fibers, the inter-mode interference spectrum of a multimode fiber shifts when the external temperature changes. Through theoretical analysis, it is found that the change in the length of the sensing fiber during temperature detection has less of an effect on the sensitivity of the sensing structure. During the experiment, temperature changes between 20 and 100 °C are measured at sensing fiber lengths of 1.5 cm, 2.0 cm, 2.5 cm, 3.0 cm, 3.5 cm, and 4.0 cm, respectively, and the corresponding sensitivities are 65.98 pm/°C, 72.70 pm/°C, 67.75 pm/°C, 66.63 pm/°C, 74.80 pm/°C, and 72.07 pm/°C, respectively. All the corresponding correlation coefficients are above 0.9965. The experimental results indicate that in the case of a significant change in the length of the sensing fiber, the sensitivity of the sensing structure changes slightly, which is consistent with the theory that the temperature sensitivity is minimally affected by a change in the length of the sensing fiber. Therefore, the effect of the length on sensitivity in a cascade-based fiber structure is well solved. The sensing scheme has an extensive detection range, small size, good linearity, simple structure, low cost, and high sensitivity. It has a good development prospect in some detection-related application fields.

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.

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(Mg1/3Nb2/3)O3-PbTiO3 (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 efficient upconversion (UC) particles based on fluorescence intensity ratio (FIR) technique are developed for application in novel temperature sensors. Herein, Yb3+/Er3+‐codoped Gd2(WO4)3 particles are prepared by coprecipitation method and subsequent calcination. The phase structure and surface morphology of the particles are systematically analyzed. The UC emission spectrum of Gd2(WO4)3:Yb3+/Er3+ particles are mainly composed of two strong emission bands centered at 530 and 551 nm, respectively. Moreover, the optimum doping concentration of Yb3+ and Er3+ is fixed at 10% and 2%, respectively. UC emission mechanism based on two‐photon process is investigated by studying the pump power excitation dependence and fluorescence decay behavior of Gd2(WO4)3:10%Yb3+/2%Er3+ particles. The excellent temperature sensing capability of Gd2(WO4)3:10%Yb3+/2%Er3+ particles is implemented from thermally coupled levels (TCLs) of Er3+. Notably, the maximum absolute sensitivity (Sa) and relative sensitivity (Sr) based on TCLs by 2H11/2/4S3/2 levels are 1.39 %K−1 (at 518 K) and 1.18 %K−1 (at 293 K), respectively. As a result, Gd2(WO4)3:10%Yb3+/2%Er3+ particles have a great potential for application in noncontact temperature sensors. [ABSTRACT FROM AUTHOR]

The efficient upconversion (UC) particles based on fluorescence intensity ratio (FIR) technique are developed for application in novel temperature sensors. Herein, Yb3+/Er3+‐codoped Gd2(WO4)3 particles are prepared by coprecipitation method and subsequent calcination. The phase structure and surface morphology of the particles are systematically analyzed. The UC emission spectrum of Gd2(WO4)3:Yb3+/Er3+ particles are mainly composed of two strong emission bands centered at 530 and 551 nm, respectively. Moreover, the optimum doping concentration of Yb3+ and Er3+ is fixed at 10% and 2%, respectively. UC emission mechanism based on two‐photon process is investigated by studying the pump power excitation dependence and fluorescence decay behavior of Gd2(WO4)3:10%Yb3+/2%Er3+ particles. The excellent temperature sensing capability of Gd2(WO4)3:10%Yb3+/2%Er3+ particles is implemented from thermally coupled levels (TCLs) of Er3+. Notably, the maximum absolute sensitivity (Sa) and relative sensitivity (Sr) based on TCLs by 2H11/2/4S3/2 levels are 1.39 %K−1 (at 518 K) and 1.18 %K−1 (at 293 K), respectively. As a result, Gd2(WO4)3:10%Yb3+/2%Er3+ particles have a great potential for application in noncontact temperature sensors. [ABSTRACT FROM AUTHOR]

An investigation of fluoroindate glass and fiber co-doped with Yb3+/Er3+ ions as a potential temperature sensor was assessed using the fluorescence intensity ratio (FIR) technique. Analysis of thermally coupled levels (TCLs—2H11/2 and 4S3/2), non-thermally coupled levels (non-TCLs—4F7/2 and 4F9/2), and their combination were examined. Additionally, the luminescent stability of the samples under constant NIR excitation using different density power at three different temperatures was carried out. The obtained values of absolute sensitivity (0.003 K−1—glass, 0.0019 K−1—glass fiber 2H11/2 → 4S3/2 transition) and relative sensitivity (2.05% K−1—glass, 1.64% K−1—glass fiber 4F7/2 → 4F9/2 transition), as well as high repeatability of the signal, indicate that this material could be used in temperature sensing applications. [ABSTRACT FROM AUTHOR]

The neutral nitrogen‐vacancy (NV0) defects in diamond are photostable color centers, suitable for a wide range of applications in science and engineering. However, the photophysical properties of the centers have not yet been fully characterized. This work measured the stimulated emission cross sections of NV0 in a single‐crystal diamond by two‐photon excitation of its matrix at 344 nm. From the measured photoluminescence spectrum and the fluorescence lifetime of 20 ± 1 ns, we determined a peak stimulated emission cross section of 1.43 ± 0.07 × 10−17 cm2 at 650 nm for the NV0 centers. In addition, we have also examined the thermal shifts of the zero‐phonon line of NV0 centers in nanoscale diamonds (~100 nm in diameter) over the temperature range of 30–120°C. A temperature measurement sensitivity of 0.2 K·Hz−1/2 was achieved, which is about two‐fold better than that of NV−, despite that the fluorescence intensity of NV0 is about six‐fold lower than that of NV− in the same nanoparticles. The result is attributed to the smaller electron–phonon coupling strength of the neutral center, compared with its negatively charged counterpart. [ABSTRACT FROM AUTHOR]

Bismuth-halide-based inorganic-organic hybrid materials (Bi-IOHMs) are desirable in luminescence-related applications due to their advantages such as low toxicity and chemical stability. Herein, two Bi-IOHMs of [Bpy][BiCl4(Phen)] (1, Bpy = N-butylpyridinium, Phen = 1,10-phenanthroline) and [PP14][BiCl4(Phen)]·0.25H2O (2, PP14 = N-butyl-N-methylpiperidinium), containing different ionic liquid cations and same anionic units, have been synthesized and characterized. Single-crystal X-ray diffraction reveals that compounds 1 and 2 crystallize in the monoclinic space group of P21/c and P21, respectively. They both possess zero-dimensional ionic structures and exhibit phosphorescence at room temperature upon excitation of UV light (375 nm for 1, 390 nm for 2), with microsecond lifetime (24.13 μs for 1 and 95.37 μs for 2). Hirshfeld surface analysis has been utilized to visually exhibit the different packing motifs and intermolecular interactions in 1 and 2. The variation in ionic liquids makes compound 2 have a more rigid supramolecular structure than 1, resulting in a significant enhancement in photoluminescence quantum yield (PLQY), that is, 0.68% for 1 and 33.24% for 2. In addition, the ratio of the emission intensities for compounds 1 and 2 shows a correlation with temperature. This work provides new insight into luminescence enhancement and temperature sensing applications involving Bi-IOHMs. [ABSTRACT FROM AUTHOR]

Multiparameter sensors that can individually monitor mechanical and thermal signals from multiple stimuli have attracted immense attention. Due to interferences caused by signal crosstalk, it is a challenge for multiparameter sensors to simultaneously differentiate mechanic and thermal stimuli within a broad working range. Herein, a liquid‐metal‐based stretchable dual‐parameter sensor that can simultaneously detect deformation (0–4.5 mm) and temperature (0–60 °C) is fabricated. The sensor adopts a multilayer structure in which a capacitive deformation‐sensing unit is stacked on top of a resistive temperature‐sensing unit. The deformation unit possesses excellent linear responses (R2 = 0.999) and ultralow detection limit (0.04 mm, ≈0.02%). Attributed to these merits, the deformation unit can be used to monitor physiological actions (e.g., finger bending, swallowing, and speaking). The temperature unit exhibits strong stability under multiple stimuli. With the cooperation of the two units, the dual‐parameter sensor can accurately differentiate deformation and temperature stimuli with an average error of 0.04 mm and 0.82 °C. Because of these remarkable performances, the sensor can achieve real‐time acquisition of the deformation and temperature change during finger movements. The dual‐parameter sensing abilities of the sensor indicate its promising potential in human motion monitoring and wearable devices. [ABSTRACT FROM AUTHOR]

In this study, the temperature sensing behaviors of emissions of Stark sublevels in Er3+/Yb3+ codoped lead lanthanum zirconate titanate (PLZT) transparent ceramic were examined. Based on the temperature-dependent upconversion fluorescence spectra excited by 980 nm, the emission intensities of the Stark sublevels 2H11/2(1, 2), 4S3/2(1, 2), and 4F9/2(1, 2, 3) were obtained upon increasing the temperature from 160 to 320 K. All the transitions present strong temperature dependence under the competitive effects of thermal excitation and nonradiative relaxation. The optical temperature sensing properties of 2H11/2/4S3/2(1), 2H11/2/4S3/2(2), 2H11/2/4F9/2(1), 2H11/2/4F9/2(2), and 2H11/2/4F9/2(3) were investigated using the fluorescence intensity ratio (FIR) technique. The largest absolute sensitivity Sa of 142.4 × 10–4 K−1 was obtained based on the FIRs of 2H11/2/4F9/2(1) at 320 K, which is approximately 26 times larger than that of traditionally used thermal coupled levels 2H11/2/4S3/2 in the considered sample. In contrast, the maximum relative sensitivity Sr was 2.21% K−1 at 203 K. A comparison of these results with those of other Er3+/Yb3+ codoped materials reveals that Er3+/Yb3+: PLZT ceramics are a promising thermometer material at low temperatures. Applying FIRs based on the photoluminescence of Stark sublevels is a practical approach to achieving greater thermometric efficiency. [ABSTRACT FROM AUTHOR]

As alternatives to electronic devices, optically active structures from responsive nanomaterials offer great opportunity for building up smart functional sensors. This work reports on the construction and application of photonic microcapsules (PMCs) for colorimetric temperature microsensors, enabling miniaturization for injectable local micro‐area sensing and integration for large‐area sensing. Monodispersed PMCs are produced by in situ photopolymerization of hydrogel shells of cholesteric liquid crystal (CLC)‐in‐water‐in‐oil double emulsion droplets prepared using microfluidic devices, with controllable physical structures and chemical compositions. Constructed PMCs exhibit thermal responsive structural color according to the selective Bragg reflection of CLC's periodical helical structures within the microdroplet's spherical confinement. CLC mixtures with phase transition temperature of 56.0 and 37.8 °C have been prepared and employed to construct PMCs exhibiting obviously visible and quantifiable optical response in 52–56 and 33–38 °C, respectively. The PMCs have been successfully applied for monitoring the living cell extracellular temperature via co‐incubation with cell suspension, and for sensing human forehead temperature via a flexible device from assembled PMCs. These PMCs can be flexibly applied in either micro‐environment or large‐area surface, enabling wide applications for a precision temperature monitoring of biological activities (e.g., cells or organs), optoelectronic devices working conditions (e.g., temperature indicators under extreme conditions), etc. [ABSTRACT FROM AUTHOR]

Lanthanide metal–organic frameworks (Ln‐MOFs) are promising for luminescence detection of volatile organic compound (VOC) vapors, but usually suffer from the silent or quenched Ln3+ emission. Herein, we report a new dual‐emissive Eu‐MOF composed of the coordinatively unsaturated Eu9 clusters that afford abundant open metal sites to form a confined "binding pocket" to facilitate the preconcentration and recognition of VOCs. Single‐crystal structural analyses reveal that specific analytes can replace the OH oscillators in the first coordination sphere of Eu3+ and form a unique hydrogen‐bonding second‐sphere adduct tying adjacent Eu9 clusters together to minimize their nonradiative vibrational decay. With the promoted Eu3+ luminescence, the MOF realizes real‐time in situ visual sensing of THF vapor (<1 s) and shows a quantitative ratiometric response to the vapor pressure with a limit of detection down to 17.33 Pa. Also, it represents a top‐performing ratiometric luminescent thermometer. [ABSTRACT FROM AUTHOR]

Here, Bi3+, Er3+ co‐activated gadolinium phosphors with multimode emission properties are prepared, which can emits blue, green, and orange light under the excitation of ultraviolet, 980 and 1550 nm, respectively. Moreover, BaGd2O4:Bi3+, Er3+ can show multicolor luminescence under different excitation conditions, such as pump light source, ambient temperature, working current, and other factors. Based on the dynamic luminescence characteristics, the dynamic anti‐counterfeiting experiments are designed based on the phosphor. At the same time, the material also shows multimode temperature sensing characteristics. Under the excitation of 980 nm laser, three strong up‐conversion signals Er3+ ions are generated at 528 nm (2H11/2), 555 nm (4S3/2), and 668 nm (4F9/2), which have different temperature dependences. Based on the fluorescence intensity ratio between thermal‐coupled energy levels (2H11/2/4S3/2) and nonthermal‐coupled energy levels (2H11/2/4F9/2) of Er3+ ions, respectively, the dual‐mode temperature thermometer was constructed with high‐temperature sensitivity. In addition, the fluorescence lifetime of Bi3+ ions also has a strong temperature dependence, which can be used as another temperature detection signal, greatly improving the stability of thermometers under harsh conditions. Therefore, the material has a bright prospect in the field of anti‐counterfeiting and temperature sensing. [ABSTRACT FROM AUTHOR]

Pure hexagonal ZnS matrix phosphors with different mole ratio (Ho3+/Yb3+=1:3, 1:6,1:9, 1:12, 1:15, 1:19) were successfully synthesized by using high temperature solid method. The phase structure of the phosphors was analyzed by X-ray diffraction. The shape and size of the phosphors were revealed by scanning electron microscope, and the presence of Zn, S, Ho and Yb elements in the phosphors was revealed by energy dispersive X-ray spectroscopy. Under the excitation of 980 nm laser, Ho3+/Yb3+ co-doped ZnS phosphors emit bright green light visible to naked eyes, showing excellent green up-conversion characteristics. In addition, the temperature sensing characteristics of ZnS: Ho3+/Yb3+ phosphor were studied in the temperature range of 303~623 K, and the maximum absolute sensitivity was calculated to be 1.26% K-1. The change of luminescence color with temperature was reflected in the color coordinate. The results of this work indicate that rare earth doped ZnS matrix materials have great potential in the application of temperature sensing. [ABSTRACT FROM AUTHOR]

A novel design for a plasmonic sensor, consisting of a metal–insulator–metal waveguide with a coupled circle-semi-ring resonator is proposed and investigated in this paper. We carried out the theoretical analysis for the wave-guiding characteristics by utilizing the two-dimensional (2D) finite-difference time-domain method. The effects of the electromagnetic wave transmission, field profile distribution, temperature and refractive index (RI) sensing characteristics on the structural parameters were studied in detail. The simulation results indicate that proposed sensor possesses a RI sensitivity up to 990 nm/refractive index unit and a temperature sensitivity of − 0.42 nm/°C with optimized geometric parameters. The compact waveguide structure may be widely utilized in areas of sensing and integrated circuits. [ABSTRACT FROM AUTHOR]

Based on the transfer-matrix method, we theoretically explore the transmission and reflection properties of light waves in a one-dimensional defective photonic crystal composed of superconductor (HgBa2Ca2Cu3O8+δ) and semiconductor (GaAs) layers. The whole system is centrosymmetric and can generate a defect transmission peak in the photonic band gap. We study the effect of the temperature on the defect mode. Results obtained show that the defect mode shifts to the lower frequency regions as the value of the environmental temperature increases, and the resonance of the defect mode can be strengthened further as the number of periods increases. In addition, our findings reveal that the central wavelength of the defect mode increases with the increase in the environmental temperature and it presents a nearly linear relationship between the central wavelength of the defect mode and the temperature in cryogenic environments. Therefore, we can use the temperature response of the defect mode to detect the temperature. It is hoped that this study has potential applications for the development of cryogenic sensors with high sensitivity. [ABSTRACT FROM AUTHOR]

• A bent fiber-optic interferometer for measurement of temperature and refractive index is proposed. • Calibration of the sensor's performance by manipulating the birefringence is explained. • A theoretical model considering the elastic optical properties of bent fiber is presented. • Experimental findings validate proposed theoretical sensing characteristics. • Repeatability and reproducibility of the sensor have been verified. A macehead-shaped bent polarization-maintaining fiber-based interferometric sensing structure called MBPIS is described and experimentally demonstrated for precise temperature and refractive index measurement. The sensor's working principle is explained by simulating the spatial distribution of the field intensity in straight and bending PANDA fibers. A maximum extinction ratio (∼21 dBm) for the interference dip wavelength (1527.825 nm) in the sensor's output spectrum was optimized by manipulating the birefringence of propagating fiber modes by adjusting PMF's bending diameter from 17 to 11 mm. The phase difference changes between these fiber modes due to temperature and RI-induced birefringence cause a shift in the interference spectrum. The sensor's highest RI sensitivity has been seen at −259.32 nm/RIU for a wide range of analytes from 1.3333 to 1.3579. In contrast, the highest temperature sensitivities evaluated for the temperature range of 0 ∼ 100 ℃ are −220 pm/℃ and −0.139 dBm/℃, respectively. [ABSTRACT FROM AUTHOR]

We propose and demonstrate a novel ammonia gas and temperature sensor based on a femtosecond laser inscribed small-period long-period fiber grating (SP-LPG) coated with a nano-assembled polyelectrolyte thin film composed of poly(diallyldimethylammonium chloride) (PDDA)/poly(acrylic acid) (PAA). The PDDA/PAA film is deposited onto the SP-LPG via layer-by-layer electrostatic self-assembly. The SP-LPG is inscribed in a single mode fiber with a period of 30 μm and the total length is only 3 mm. The designed period is much smaller than that of the conventional long period fiber grating (LPFG) of several hundred microns, so we can not only see high-order cladding modes in the transmission spectrum, but also a series of Bragg resonance peaks in the reflection spectrum. The concentration of ammonia gas is detected by the wavelength shift of the transmission resonance dip. The ambient temperature is monitored by the wavelength shift of the Bragg resonance peak. Because the Bragg resonance peak is insensitive to refractive index, we can measure ammonia gas and temperature simultaneously. The experimental results show that the detection limit of the sensor is less than 0.1 ppm. The sensor is sensitive only to ammonia when exposed to different gases. The temperature sensitivity of the sensor is about 8.7 pm/℃ from 30℃ to 70℃. Compared with traditional LPFG, SP-LPG has a more compact structure and the special ability to monitor temperature in real time, which makes the device more advantageous in practical applications. • The proposed SP-LPG was first ever applied to gas sensing. • The SP-LPG was fabricated efficiently and economically by femtosecond laser writing. • Simultaneous detection of ammonia gas and temperature was achieved. • The SP-LPG was easier for integration and miniaturization. [ABSTRACT FROM AUTHOR]

With the development of new energy vehicles, the safety concern of power batteries has become urgent, making the exploitation of new temperature sensors for the batteries important. In this paper, persistent luminescence nanoparticles (PLNPs) of Bi 1.91 Ga 4 O 9 : 0.04 Er3 +, 0.05 Eu3+ with up- and down-conversion luminescence were prepared by a simple and low-cost co-precipitation method. Single rare earth element doping of Er3+ achieves up-conversion luminescence at 526 nm/550 nm under 980 nm excitation. After co-doping with rare earth element Eu3+, it can realize the down-conversion luminescence at 590 nm/614 nm under 254 nm excitation. They showed obvious temperature dependence at 293–503 K and 423–573 K, respectively. The corresponding maximum relative sensitivities are 0.98 % K−1 and 0.55 % K−1. Interestingly, all temperature ranges cover the spontaneous ignition point of the power battery at 473 K. Thus, the PLNPs-based sensor was successfully validated for monitoring overheating and spontaneous combustion of power battery with the dual-channel temperature measurement modes. The two kinds of temperatures were verified with each other for the improved sensitivity and accuracy, so they were used to accurately measure the temperature of the power battery in real time for early warning and the improved safety. Thus, we provided a new application scenarios of PLNPs in the field of temperature sensing for monitoring the temperature of battery. • Er-Eu co-doped Bi2Ga4O9 persistent luminescence nanoparticles with up- and down-conversion luminescence was prepared. • The material for dual-mode temperature measurement. • Accurately measuring the temperature of the power battery for the improved safety. [ABSTRACT FROM AUTHOR]