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Single mode lasers, particularly red-green-blue (RGB) colors, have attracted wide attention due to their potential applications in the photonic field. Here, we realize the RGB single mode lasing in a hybrid two-dimension and three-dimension (2D–3D) hybrid microcavity (μ-cavity) with a low threshold. The hybrid 2D–3D μ-cavity consists of a polymer fiber and a microsphere. Typical RGB polymer film consisting gain materials are cladded on a fiber. To achieve single mode lasing, the polymer fiber therein serves as an excellent gain cavity to provide multiple lasing modes while the microsphere acts as a loss channel to suppress most of the lasing modes. Mode switching can be realized by adjusting the pump position. It can be attributed to the change of coupled efficiency between gain μ-cavity and loss μ-cavity. Our work will provide a platform for the rational design of nanophotonic devices and on-chip communication.

This study proposes a novel twisted and coiled polymer fiber (TCPF) actuator fabricated from a polymer-coated optical fiber. The TCPF actuator is a soft actuator that is driven by heating; the TCPF actuator in combination with a cooling system has been widely studied for applications in robotics. Sensing is a major issue in such units; in particular, temperature sensing is important for the safe usage of the TCPF. To achieve this, the electrical properties of the heating wire are typically utilized. However, this method is affected by the input voltage noise because the circuit used for actuation is the same as that used for sensing. To separate these circuits, this study developed a temperature-sensing method for the TCPF based on an optical fiber. For propagating only the heat of the polymer to the optical fiber, we embedded the optical fiber in the TCPF. This study experimentally demonstrated that the TCPF actuator fabricated using the polymer-coated optical fiber can be driven by heating. Furthermore, using the developed sensing method, we achieved temperature and force control under isometric conditions.

A simply fabricated, highly sensitive, and inexpensive optical fiber temperature sensor is reported with a Fabry–Perot (FP) microcavity of controlled length. The microcavity with controllable length is fabricated by single-mode fiber (SMF) and polydimethylsiloxane (PDMS) for temperature sensing. After the PDMS is cured, the SMF is connected to the supercontinuum light source (SCLS) and the optical spectrometer analyzer (OSA) for online observation of the reflection spectrum. The micro-displacement platform is used to pull the SMF to form an air cavity. After the air cavity is stabilized, ultraviolet (UV) activated glue is used for packaging outside the PDMS. The FP microcavity is formed by the end face of the SMF and the face of PDMS. The length of the FP microcavity can be controlled online by the micro-displacement platform to a minimum of 15 µm. The free spectral range (FSR) may reach 74.8 nm and the interference fringe contrast (IFC) is up to 19.8 dB to allow sensitive measurements across a wide temperature range. The experiments demonstrate a high temperature sensitivity of 5.388 nm/°C from 33 to 93 °C with high repeatability and linearity (R2=0.9937). Stability experiments showed that the maximum changes in wavelength and intensity are only 45 pm and 0.035 dB, respectively. It is anticipated that the easily constructed, compact, and inexpensive fiber-optic temperature sensor will be employed in practical applications.

YGdO3:Er3+ nanoparticles were successfully synthesized by pulsed laser ablation in liquid method. The structural and morphological properties of the product are investigated by X-Ray diffraction and transmission electron microscopy. The upconversion photoluminescence properties were investigated in detail. Obvious stark splitting phenomena were observed in the green and red emission bands. The decay behaviors of three emission bands were studied. Based on thermal coupled energy level related upconversion fluorescence intensity ratio, the temperature sensing properties of product were studied. Linear function has beenused to reveal the relationship between fluorescence intensity ratio and temperature. Using stark sublevels related emission bands, sensitivity of the temperature sensor was successfully enhanced. These results suggest the YGdO3:Er3+ nanoparticles prepared via pulsed laser ablation in liquid are promising luminescent materials for optical thermometry.

Er3+/Yb3+ co-doped InNbO4 phosphors were synthesized using solid state reaction method. Crystal structure was characterized using X-ray diffraction (XRD), which confirm all obtained phosphors had a monoclinic-wolframite structure and no impurity phase was introduced upon doping. Upon 980 nm excitation, upconversion (UC) emission from Er3+ ions was observed in green and red range. UC emission was obviously enhanced after co-doping Yb3+ ions and reached the maximum for 10 mol% Yb3+ ions. The relation between emission intensity and pump power was performed, revealing that the UC emission result from two-photon processes. Optical temperature sensing property was investigated by exploiting fluorescence intensity ratio (FIR) between 2H11/2 and 4S3/2 levels of Er3+ ions. Its maximum value of absolute sensitivity obtained was 0.0091 K-1, suggesting InNbO4:Er3+/Yb3+ phosphors show potential application in optical thermometry.

The urgent requirement of monitoring air pollution worldwide evokes intensive research interest in developing chemiresistive gas sensing techniques. To overcome the limits in sensitivity and selectivity of room temperature (RT) chemiresistive sensing materials, a new strategy using single-atom catalysts (SACs) via surface coordination is proposed. As a proof-of-concept, single Pd atoms on TiO2 (Pd1-TiO2) possess high efficiency in generating adsorbed O2- as well as high activity and selectivity in catalyzing CO oxidation at RT. As a result, Pd1-TiO2 shows record high sensitivity among the reported RT sensing materials, which is even comparable to those of the best materials working at high temperature. It also provides an approximately 1 order of magnitude lower limit of detection than the best CO sensing materials. Moreover, Pd1-TiO2 presents high selectivity toward 12 kinds of interference gases. This work not only paves a way to design high-performance RT gas sensing materials but also extends the application of SACs.

Contactless optical thermometry is successfully applied for accurate local temperature sensing in many scientific and technological areas. The majority of optical thermometers utilize a ratiometric...

A probe-shaped sensor for simultaneous temperature and pressure measurement was reported in this article. The effective length of the sensor was ∼2mm, consisting of a fiber Bragg grating (FBG) and a Fabry-Perot interferometer (FPI) with a nano silica diaphragm. The response sensitivities of the sensor for pressure and temperature were measured as −0.98 nm/MPa and 11.10 pm/°C, respectively. This sensor had an extremely low cross-sensitivity between pressure and temperature, which provided a significant potential in dual-parameter sensing.

Precise, sensitive, and reversible thermochromic luminescent sensing can be achieved by PEAMnBrxI3−x (x = 0/1/2/3). Their luminescence ratios of green to red exhibited a reversible linear response to the temperature increment process (from 40 °C to 120 °C), bright luminescence under high temperature, and reversible heating–cooling circulation performance. Based on the thermochromic luminescence properties, the PEAMnBr2I–polymer film was used for precise and real-time temperature sensing. A deep understanding of their thermochromic luminescence mechanism can facilitate the design of thermochromic materials with high performance and their wider applications.

Temperature is one of the physical parameters that affects the emission luminescence properties of upconversion (UC) materials. Temperature-dependent emission color tuning and good temperature sensitivity in multifunctional β-NaYF4:Yb/Er@β-NaYF4:Yb/Tm microcrystals were achieved under 980 nm excitation. Based on the different emission bands (blue, green and red bands) and spectral sensitivities of the core–shell structured microcrystals to temperature, intense white-light emission was obtained at room temperature and a real-time naked-eye recognizable emission color change from white to the purplish-pink region was realized with the temperature increasing from 300 to 500 K. Furthermore, optical temperature sensing properties of the sample with good sensitivity (from 0.0034 to 0.0044 K−1) were investigated by using a fluorescence intensity ratio between 521 nm (2H11/2 → 4I15/2 transition) and 540 nm (4S3/2 → 4I15/2 transition) in the temperature range from 300 to 500 K. The results indicate that the sample has high sensitivity in a relatively wide range of temperature intervals, especially in the low temperature region. We believe that the multifunctional core–shell structured microcrystals exhibit promising applications in white-light emitting diodes, the anti-counterfeiting field, and temperature sensing.

In this paper, we demonstrate that nitride-based R/G/B micro-LEDs allow temperature sensing through a forward voltage response on both temperature and display devices. In temperature sensing, micro...

Realizing multicolored luminescence in two-dimensional (2D) nanomaterials would afford potential for a range of next-generation nanoscale optoelectronic devices. Moreover, combining fine structured spectral line emission and detection may further enrich the studies and applications of functional nanomaterials. Herein, a lanthanide doping strategy has been utilized for the synthesis of 2D ZnSe:Er

We present the first report on reflectometric optical fiber sensing based on mechanically induced cascaded long-period grating (LPG) structure. This method utilizes in-house designed mechanical casings and a bare fiber. When a fiber is sandwiched between the casings and pressed by tightening screws, an LPG is induced due to a photo-elastic effect. By exploiting Fresnel refection at a fiber end, a cascaded LPG structure can be implemented using a single LPG, enabling reflectometric configuration. When this sensor is subjected to external physical processes, the attenuation bands change clearly, and their shift can be used for non-destructive evaluations. We show experimentally that this sensor can measure loads of up to 10 N without producing any permanent change in the fiber properties, indicating its pressure sensing capability. We also show that this sensor can potentially measure strain and temperature. In our experiments, the strain and temperature sensitivities are 9.4 nm/% and 0.045 nm/°C, respectively.

Flexible coatings with dual capabilities for remote real-time temperature sensing and photothermal conversion have a huge potential in the field of advanced thermal actuated optoelectronic applicat...

A series of garnet-structured Li6Ca(La0.99-xYbxEr0.01)2Nb2O12 (0≤x≤0.05) phosphors were originally synthesized and examined for upconversion (UC) luminescence and optical temperature sensing under 978 nm laser excitation. It was identified that the optimal content of Yb3+ sensitizer is x=0.04 for Er3+ emission and the non-thermally coupled 2H11/2/4F9/2 energy levels of Er3+ possess a superior capability of optical thermometry, whose maximum absolute sensitivity (~15.20 × 10−3 K−1 at 523 K) is generally ~1.7-6.1 times the values reported to date for most of other UC systems.

In this paper, BaY2O4:Yb3+/Er3+, a high efficient red upconversion (UC) material, is first utilized as an optical thermometer in the biological window, accomplished through the fluorescence intensity ratio (FIR) of thermally coupled Stark sublevels of 4F9/2 (FIR(654/663)). The maximum absolute sensitivity of FIR(654/663)) is 0.19% K-1 at 298 K, which is much higher than most previous reports about FIR-based temperature sensors located in the biological windows. More importantly, the groove of FIR(654/663) for thermometry is nicely located in the physiological temperature range, indicating its potential thermometry application value in biomedicine. Furthermore, a simply ex vivo experiment is implemented to evaluate the penetration depth of the red emission in biological tissues, revealing that a detection depth of 6 mm can be achieved without any effect on the FIR values of I654 to I663. Beyond that, the temperature sensing behaviors of the thermally coupled levels 2H11/2 and 4S3/2 (FIR(523/550)) are also investigated in detail. In the studied temperature range, the absolute sensitivity of FIR(523/550) monotonously increases with the rising temperature and reaches its maximum value 0.31% K-1 at 573 K. All the results imply that BaY2O4:Yb3+/Er3+ is a promising candidate for deep-tissue optical thermometry with high sensitivity.

A temperature sensor with high sensitivity based on the birefringence induced Vernier effect in a symmetrical metal-cladding waveguide (SMCW) structure is theoretically proposed. Due to the guiding...

In this paper, upcovnerison luminescence in Er3+/Yb3+ co-doped NaYF4 nanophosphors was regulated by changing the Er3+ concentration. With increasing the Er3+ concentration, the green and red emissions increased first and then decreased, but the intensity ratio of red to green emission decreased monotonically. To clarify the role of Er3+ doping, the factors including crystal structure, morphology and size of particle, photon absorption, energy transfer, multi-phonon relaxation, population of emissive levels and emission probability of radiative transitions were considered and analyzed. More importantly, we proposed a simple method for discussing radiation transitions based on luminescence temperature sensing.

Lanthanide ion doped upconversion nanomaterials have attracted great interest because of their extensive application, especially in color display and temperature sensing. However, control synthesis...

A twin-core sensor with high birefringence employing a photonic crystal fiber (PCF) is presented for simulated temperature measurements based on surface plasmon resonance (SPR). The internal wall of the central hole of the PCF is plated with gold and coated with graphene oxide (Au-GO) to develop an SPR sensing channel. The results of a numerical analysis with COMSOL Multiphysics show that the birefringence of this sensing structure can reach 0.0052. In addition, an average sensitivity of -12.695 nm/ °C can be achieved in the range of 0 °C~80 °C. Compared with uncoated GO sensors and existing sensing units, this sensor shows improved stability, sensitivity and birefringence.

Er3+ doped potassium sodium niobate (KNN: Er) ultrafine powders have been prepared by pulsed laser ablation in water. X-ray diffraction (XRD) pattern of the sample demonstrated that the as-synthesized powders were crystalized in orthorhombic phase. Scanning electron microscopy (SEM) and transmittance electron microscopy (TEM) images exhibited that the morphology of ultrafine powders are cube-like. Under the excitation of 980 nm laser, the sample exhibits green emission, which is originated from the transition of thermal coupled energy levels (2H11/2, 4S3/2) to ground state level 4I15/2. Temperature dependent up-conversion emission intensity associated with thermal quenching of total green emission band and the fluorescence intensity ratio (FIR) between two sub-emission bands related to population of thermal coupled energy levels are investigated for temperature sensing in the temperature range of 300 K to 480 K. The temperature sensing performances related to different technique were discussed. A maximum relative sensitivity reaches 1.01% K-1 at 464 K for emission intensity thermometry and that is 0.84% K-1 at 374 K for FIR thermometry technique. All these results show that KNN: Er ultrafine phosphors prepared via pulsed laser ablation in water have prospect for non-contact temperature sensing.

Thermally activated delayed fluorescence (TADF) is a highly temperature-dependent process and can be used in optical thermometry. TADF-based optical thermometers reported so far show fairly high-temperature sensitivity but have poor brightness and significant oxygen cross-talk. A new class of TADF emitters, Zn(II) Schiff base complexes, possess excellent brightness and high temperature sensitivity of the decay time at ambient temperature (4.1%/K change of TADF lifetime at 25 °C), enabling a resolution better than 0.03 °C. Oxygen cross-sensitivity is eliminated by covering the sensing layer (luminophore in polystyrene) with an off-stoichiometry thiol–ene polymer as an oxygen-consuming layer, and a poly(vinylidene chloride-co-acrylonitrile) layer as an oxygen barrier. The material is stable after more than 2 months of storage at ambient air, which enables long-term temperature monitoring.

In this paper, we propose the use of a dual wavelength scheme for active distributed temperature sensing based on Co2+-doped fibers. A Brillouin Optical Frequency-Domain Analysis (BOFDA) set-up, operating at 850 nm, is used to detect the temperature changes along Co2+-doped optical fibers with various absorption coefficients, while optical heating is performed through a 1550-nm optical pump. A simple model describing optical heating along the Co2+-doped fiber is introduced and experimentally validated. As a proof of concept, we demonstrate that the sensor is capable to distinguish a 1-m portion of fiber immersed into water, from a section of equal length surrounded by air.

This paper presents reports on the preparation of a multifunctional coating system, CrNx, with temperature sensing capability. A systematic study of the thermo-resistive effect of chromium nitride (CrNx) thin films with a negative temperature coefficient of resistance (TCR) has been carried out. The CrNx nanostructures were grown by reactive magnetron sputtering under distinct Ar+N2 conditions. To confer a zigzag columnar morphology to the CrNx we explored the oblique angle deposition technique. The structural properties have been studied through X-ray diffraction and Scanning Electron Microscopy. The thermo-resistive response was evaluated by measuring the electrical resistivity as a function of temperature by the twopoint method. The results observed for the CrNx films produced with N2 flux between 4 and 8 sccm present an stable and negative TCR. Values of -9.1710-4 , -5.3110-3 , and -1.47610-2 were observed for the films grown with 4, 6, and 8 sccm, respectively. The grain-boundary was used to theoretically describe our results. The results open new technological possibilities for the application of CrNx coatings for esistive temperature detector (RTD) systems., The authors thank the Portuguese Foundation for Science and Technology (FCT) for the strategic funding UID/FIS/04650/2020. A. Ferreira thanks the FCT for the contract under the Stimulus of Scientific Employment (CTTI-31/18 - CF (2) junior researcher contract) . M. A. Correa thanks the CNPq and CAPES. The authors acknowledge funding by the Basque Government Industry and Education Departments under the ELKARTEK and PIBA (PIBA-2018-06) programs, respectively, and to European Regional Development Fund under the Operational Program Cdompetitiveness and InternationalizationdResearch and Development (R&D) and Innovation to SMEs - R&D Individuals Projects, grant agreement no 038397.

Current transport mechanisms (CTMs) and temperature sensing qualifications of Al/(ZnS-PVA)/p-Si structures are identified with the help of temperature-dependent forward bias current-voltage measurements. To determine the current transport mechanism, the electrical parameters of the structure such as saturation current (I-o), zero - bias barrier height (Phi(B0)), ideality factor (n) are determined from these characteristics measured in the temperature range of 60-320 K. The temperature dependencies of the calculated Phi(Bo) and n values indicate the existence of double Gaussian distribution (DGD) of barrier height (BH) at M/S interface. Using the modified Richardson plots, Phi(B0) and A* values have been found in the high temperature region (HT) (160-320 K) as 0.95 eV, 31.64 A.cm(-2)K(-2), respectively and in the low temperature region (60-140 K) as 0.3871 eV, 20.996 A.cm(-2)K(-2), respectively. The A* value in the HT region is very close to its theoretical value and hence the CTMs can be explained by the DGD of BH. Sensitivity (S) values are calculated for each voltage at forward biases from the temperature-dependent variation of the logarithm of the

Antiresonant hollow core fibers (ARHCFs) have gained some attention due to their notoriously attractive characteristics on managing optical properties. In this work, an inline optical fiber sensor based on a hollow square core fiber (HSCF) is proposed. The sensor presents double antiresonance (AR), namely an internal AR and an external AR. The sensor was designed in a transmission configuration, where the sensing head was spliced between two single mode fibers (SMFs). A simulation was carried out to predict the behaviors of both resonances, and revealed a good agreement with the experimental observations and the theoretical model. The HSCF sensor presented curvature sensitivities of −0.22 nm/m−1 and −0.90 nm/m−1, in a curvature range of 0 m−1 to 1.87 m−1, and temperature sensitivities of 21.7 pm/°C and 16.6 pm/°C, in a temperature range of 50 °C to 500 °C, regarding the external resonance and internal resonance, respectively. The proposed sensor is promising for the implementation of several applications where simultaneous measurement of curvature and temperature are required.

Quantitative detection of cancer cells using portable devices is promising for the development of simple, fast, and point-of-care cancer diagnostic techniques. However, how to further amplify the detection signal to improve the sensitivity and accuracy of detecting cancer cells by portable devices remains a challenge. To solve the problem, we, for the first time, synthesized folic-acid-conjugated Au nanoframes (FA-Au NFs) with amplification of pressure and temperature signals for highly sensitive and accurate detection of cancer cells by portable pressure meters and thermometers. The resulting Au NFs exhibit excellent near-infrared (NIR) photothermal performance and catalase activity, which can promote the decomposition of NH4HCO3 and H2O2 to generate corresponding gases (CO2, NH3, and O2), thereby synergistically amplifying pressure signals in a closed reaction vessel. At the same time, Au NFs with excellent peroxidase-like activity can catalyze the oxidation of 3,3',5,5'-tetramethylbenzidine (TMB) to produce TMB oxide (oxTMB) with a strong photothermal effect, thereby cooperating with Au NFs to amplify the photothermal signal. In the presence of cancer cells with overexpressing folate receptors (FRs), the molecular recognition signals between FA and FR can be converted into amplified pressure and temperature signals, which can be easily read by portable pressure meters and thermometers, respectively. The detection limits for cancer cells using pressure meters and thermometers are 6 and 5 cells/mL, respectively, which are better than other reported methods. Moreover, such Au NFs can improve tumor hypoxia by catalyzing the decomposition of H2O2 to produce O2 and perform photothermal therapy of cancer. Together, our work provides new insight into the application of Au NFs to develop a dual-signal sensing platform with amplification of pressure and temperature signals for portable and ultrasensitive detection of cancer cells as well as personalized cancer therapy.

We propose a novel, highly sensitive, and stable fiber-optic temperature sensing method that utilizes the temperature dependence of the gain of an amplified-spontaneous-emission feedback circuit. It is experimentally demonstrated that the method achieves a long-term temperature resolution of 0.0147 °C.