Sensitive Thermometer Research Articles

Optical thermometry and multi-mode anti-counterfeiting based on Bi3+/Ln3+ and Ln3+ doped Ca2ScSbO6 phosphors

A series of novel Bi3+/Ln3+-activated Ca2ScSbO6 (CSSO) phosphors were synthesized by solid-state method and their luminescent behaviors were investigated in detail. Under the 302 nm excitation, the CSSO:Bi3+ shows remarkable near-ultraviolet photoluminescence with a peak emission at 365 nm. Eu3+-activated CSSO phosphor possesses high efficiency and no obvious reduction of emission intensity even after replacing Sc with Eu completely, which indicates a low-concentration quenching effect. In addition, its emission intensity at 423 K (I423K) still maintains 88 % compared with that of at room temperature (I298K), indicating good thermostability. In contrast, the CSSO:Bi3+ phosphor exhibits a significant reduction in emission intensity, maintaining only 49 % of its luminescence at 423 K (I423K/I298K). By codoping Bi3+ and Ln3+ (Ln = Eu, Tb, Dy, Sm), the energy transfer was observed from the Bi3+ to Ln3+ ions, endowing the CSSO:Bi3+, Ln3+ phosphors with tunable multicolor emissions. Leveraging the differing thermostabilities of the emission spectra for Bi3+ and Ln3+ ions, we designed and assessed a range of sensitive optical thermometers. Among these, the CSSO:Bi3+, Eu3+ phosphors exhibited the best performance, boasting maximum absolute and relative sensitivities of 9.96 % K−1 and 2.002 % K−1, respectively. Additionally, we displayed the multi-mode anti-counterfeiting function of synthesized phosphors, and a multi-color switching system was designed with the advantages of direct visualization and easy identification of encrypted information. These results indicate that Bi3+ and Ln3+ coactivated CSSO phosphor has the potential application for non-contact temperature measurement and anti-counterfeiting.

Heat Resistant Organic Dyes for High Temperature Luminescent Temperature Sensing

AbstractCompliant and large‐area high‐temperature gradient sensing is essential for scientific and industrial applications but remains a big challenge. Although organic luminophores have intrinsic advantages of flexibility and solution processability, they generally suffer from significant emission quenching at high temperatures due to thermally facilitated nonradiative decay. Herein, a heat‐resistant blue emitter of C3 based on triarylphosphine oxide has been developed, due to the thermal population of the higher emissive state from its lowest excited state. Based on this, hybridization of C3 with a faster thermally‐deactivated yellow dye of T4AC which exhibits a large Stokes shift enables blocking of energy transfer and independent thermal response of the two respective emitters. Thus, sensitive ratiometric film thermometers for high‐temperature sensing can be constructed. The relative sensitivity (Sr) reaches 1.27%°C−1 at 128 °C and the temperature resolution is < 0.77 °C in a wide sensing range of 20–240°C. Moreover, naked‐eye thermal mapping and multiple anti‐counterfeiting of these ratiometric films have also been demonstrated.

The development of a dual-mode optical temperature sensor based on fluorescence intensity ratio and lifetime

The utilization of optical parameters is crucial for achieving accurate temperature detection, which in turn facilitates the development of new phosphors used for non-contact optical thermometers. In this study, a series of phosphors of KSrGdTeO6 (KSGT) co-doping Mn4+ and Sm3+ luminescent centers, were synthesized through high temperature solid-state reactions. Notably, the temperature-dependent emission spectra and attenuation curves of KSGT:Mn4+/Sm3+ were measured across a wide temperature range of 298–573 K. In the absence of energy transfer between Mn4+ and Sm3+, Mn4+ and Sm3+ activators can emit their characterized emissions by 405 nm excitation. With increasing temperature, the fluorescence intensity of Mn4+ ions decreases at a faster rate compared to that of Sm3+ ions as the temperature increases. Consequently, by utilizing the fluorescence intensity ratio (FIR) between the two activators Mn4+ and Sm3+, the optimal temperature sensing relative sensitivity (Sr) and absolute sensitivities of (Sa) of KSGT:Mn4+/Sm3+ were found to be 2.591 % K−1 at 298 K and 0.0246 K−1 at 573 K. Moreover, the luminescent lifetime of Mn4+ emission decreases rapidly with increasing temperature, which makes it also possible to be a lifetime-based thermometry with Sa and Sa of 2.3233 %K−1 at 448 K and 0.1444 K−1 at 398 K. The dual-mode sensing properties of KSGT:Mn4+/Sm3+ make it a highly sensitive temperature thermometer, which provides design ideas for future researchers in this field.

A ratiometric luminescence thermometer based on lanthanide encapsulated complexes.

Lanthanide-containing complexes have been widely developed as ratiometric luminescence thermometers, which are non-invasive, contactless and accurate. The synthesis of these Ln complexes generally requires high temperatures, multiple steps and other harsh conditions. Moreover, bimetallic lanthanide complexes, which have been reported to be better thermometers, are even more challenging to synthesize. This complexity can be simplified by preparing a host-guest complex of lanthanides. In this work, Tb or both Tb and Eu are encapsulated in an MOF host, making them emissive. The ratio of Tb/Eu was also easily tuned by simply changing their ratio in the solution, resulting in a tunable emission. Accordingly, we were able to synthesise both the emissive Tb complex and Tb/Eu complexes at different ratios using a single host. The complexes were found to be suitable as ratiometric luminescent thermometers in the temperature range of 160-380 K, with reasonably good sensitivity and uncertainty. The thermometer's sensitivity and uncertainty were significantly improved using bimetallic Tb and Eu host-guest complexes. Calculations using the host and Eu emission ratio were found to provide better thermometer parameters than the commonly reported Tb and Eu emission ratio. Thus, using a single host, we were able to synthesise different lanthanide complexes that can sense temperature, and we improved the thermometer parameters by incorporating multiple lanthanides in a single host. This research will enable the scientific community to reexamine the applicability of unexplored host-guest lanthanide complexes.

Anomalous thermal activation of green upconversion luminescence in Yb/Er/ZnGdO self-assembled microflowers for high-sensitivity temperature detection.

Non-contact optical temperature detection has shown a great promise in biological systems and microfluidics because of its outstanding spatial resolution, superior accuracy, and non-invasive nature. However, the thermal quenching of photoluminescence significantly hinders the practical applications of optical temperature probes. Herein, we report thermally enhanced green upconversion luminescence in Yb/Er/ZnGdO microflowers by a defect-assisted thermal distribution mechanism. A 1.6-fold enhancement in green emission was demonstrated as the temperature increased from 298 K to 558 K. Experimental results and dynamic analysis demonstrated that this behavior of thermally activating green upconversion luminescence originates from the emission loss compensation, which is attributed to thermally-induced energy transfer from defect levels to the green emitting level. In addition, the Yb/Er/ZnGdO microflowers can act as self-referenced radiometric optical thermometers. The ultrahigh absolute sensitivity of 1.61% K-1 and an excellent relative sensitivity of 15.5% K-1 based on the 4F9/2/2H11/2(2) level pair were synchronously achieved at room temperature. These findings provide a novel strategy for surmounting the thermal quenching luminescence, thereby greatly promoting the application of non-contact sensitive radiometric thermometers.

A highly sensitive ratiometric optical thermometer based on a Sr2MgWO6 double perovskite doped with Dy3+ exploiting thermally coupled and uncoupled levels.

The increasing demand for highly sensitive optical thermometers operating within a wide temperature range necessitates the development of new phosphors. In this work, the potential temperature sensing performance of a novel yellow-emitting phosphor, Sr2MgWO6 double perovskite, doped with varying concentrations of Dy3+ was investigated for the first time. Increasing the concentration of Dy3+ from 0% to 7% shifted the color of luminescence from blue to yellowish-orange within the CIE1931 color space. The energy transfer efficiency from (WO6)6- to Dy3+ also increased significantly to 98.4%. Moreover, the sample doped with 3% Dy3+ showed the highest emission intensity, with a concentration beyond this threshold inducing concentration quenching. This phenomenon was primarily governed by dipole-dipole interactions. The highest quantum yield was found to be 30.7% for the sample doped with 3% Dy3+. Upon 266 nm wavelength excitation, the temperature sensing ability of the samples doped with 3%, 5%, and 7% Dy3+ was examined based on the fluorescence intensity ratio between the thermally coupled and uncoupled levels. It showed that the relative thermal sensitivity of Sr can be tuned by changing the Dy3+ concentration. Sr-max = 3.24% K-1 was obtained for the sample doped with 3% Dy3+ at 193 K within the 80-273 K operating range for thermally uncoupled levels. For thermally coupled levels, the Sr-max value reached 1.35% K-1 at 333 K for the sample doped with 7% Dy3+ in the range of 293-593 K. These results demonstrate the enormous potential of the studied materials for thermal sensing applications.

Monitoring decomposition of Eu3+ doped LaPO4 nanocrystals in glass using Eu3+ as an optical probe for applications in temperature sensing

The methods to directly introduce crystals of known chemistry, size, and optical properties into a glass matrix are useful to circumvent some limitations related to the control of the growth of crystalline phases in glass-ceramics. The emission spectrum of LaPO4:Eu3+ is characteristic for highly symmetrical coordination of Eu3+ and very distinct from the emission spectrum of Eu3+ in amorphous host, which allows for its application as an optical probe. Here, Eu3+ - doped LaPO4 crystals were prepared using solid state reaction and added into various phosphate glass melt before quenching. From the changes in the micro-luminescence spectra, the decomposition occurs along with the diffusion of the Eu3+ ions into the glass confirming that the measurement of the micro-luminescence allows one to precisely track the crystal's decomposition inside the composite. It is demonstrated, for the first time to our knowledge, that the thermometric sensitivity of the Eu3+ ions can be enhanced by adding the LaPO4:Eu3+ crystals into phosphate fluoride glasses due to special separation of the crystallites during the composite preparation and also to the reduction of the self-absorption of the 5D1→7F1 emission. The composite material is promising for applications in temperature sensing.

Manipulation phonon energy for improved thermometric sensitivity of only-core nanoparticles

Luminescent nano thermometry using upconversion nanoparticles (UCNPs) has gained attention in recent years due to its potential advantages over conventional methods. One major challenge in practical applications of nanothermometers is achieving high sensitivity. While efforts have been made to improve the sensitivity of individual core nanoparticles, there are few reports on incorporating phonon energy and local crystal field distortions to improve the sensitivity of only-core upconversion nanoparticles. In this study, we propose a new approach to improve the sensitivity of only-core UCNPs thermometers through phonon tuning and self-photogenic heating. We use the ratio of the intensity of two bands (centered at 520 nm and 540 nm) based on dopant Er3+ as a referenced signal for optical sensing of temperature. We use a host material NaYF4 doped with K+ to produce local crystal field changes at the interface, modifying the phonon energy mode. As the temperature increases, the vibrational mode cannot propagate smoothly along the crystal axis throughout the crystal, disrupting the direction of lattice heat conduction and producing a significant local thermal effect on the nanoscale. This leads to a significant increase in sensitivity, and we achieve an enhanced thermal sensitivity more than twice that of conventional core-only nanoparticles.

Influence of plasmonic and thermo-optical effects of silver nanoparticles on near-infrared optical thermometry in Nd3+-doped TeO2–ZnO glasses

Optical thermometers based on the luminescence of trivalent rare earth-doped materials are often explored due to their high sensitivity and performance in the visible and infrared spectral regions. Among them, Nd3+ ions are widely used because they operate efficiently in the main biological windows, although an increase in their sensitivity at low temperatures is still desired. This work aims to investigate the influence of the addition of silver nanoparticles (Ag-NPs) on the temperature-dependent luminescence of Nd3+ doped TeO2–ZnO glasses over wide temperature ranges (295–480 K). The study shows that the plasmonic effects induced by Ag-NPs lead to an absolute sensitivity increase of up to ∼28.6% in Nd3+-based thermometers operating through a set of three thermally coupled energy levels. In addition, thermometry studies using high-power excitation beams reveal that the thermo-optical properties of Ag-NPs favor optical thermometer sensitivity enhancement due to local heating effects and compensates for the losses caused by luminescence quenching at high concentration of Nd3+ ions. Moreover, an experiment analyzing the speckle patterns generated by Nd3+ doped TeO2–ZnO glasses, conducted for the first time to the best of our knowledge, confirms the influence of the thermo-optical effects of Ag-NPs in optimizing the sensitivity of optical thermometers.

Synergistic red dominancy over green upconversion studies in PbZrTiO3: Er3+/Yb3+ phosphor synthesized via two different modified technique and flexible thin-film thermometer demonstration on C1: PbZrTiO3 @PDMS substrates

Owing to its efficient wide range sensing using a noncontact mechanism with a decimal accuracy level, quick, non-invasive temperature sensors utilizing upconversion (UC) phosphor were examined. These sensors are perfect for cutting-edge applications such as measuring the intracellular temperature and identifying microelectronic issues. It may be possible to modify the performance of phosphor temperature sensors through nanoscale engineering. Despite were potential, it has been discovered that modern nanothermometers are ineffective in maintaining stability over a wide temperature range. Motivated by previous studies on efficient UC based solar cell demonstrations of Er3+/Yb3+: PbZrTiO3 (lead zirconate titanate) phosphors, the UC properties of Er3+/Yb3+: PbZrTiO3 for a wide range of temperature sensing and practical thermometer applications have been investigated. The UC emission properties of the Er3+/Yb3+: PbZrTiO3 phosphors synthesized via different routes, with the same dopant concentration, were compared. We have also investigated the formation of two different crystal symmetry, and an approach for the fine-tuning of the emission from the green to the red region upon changing the synthesis technique. The strategy of choosing an optimized synthesis route, based upon structural investigations, could be a way forward where dopant modification in phosphors is ruled out. Based on the UC optimization, the green and red dominant phosphors under 980 nm excitation with different pulse widths and power densities or at different temperatures were studied; the possible mechanisms were discussed in detail. The sensitivity of Er3+/Yb3+: PbZrTiO3 was independent of the pumping laser characteristics since it was essentially consistent when utilising both continuous wave and laser pulse width modulation or varying power densities. To assess the temperature of the microelectronic components, a flexible thin-film thermometer was made of Er3+/Yb3+: PbZrTiO3 on a polyDiMethylSiloxane substrate. This thermometer shows great repeatability and can measure the temperature of an electronic circuit board correctly. The findings suggested that the current non-contact UC temperature sensor might potentially replace conventional thermometers because of its steady green emission over a wide temperature range (313–673 K) and thermometric sensitivity.

Achieving Highly Efficient Warm-White Light Emission in All-Inorganic Copper-Silver Halides via Structural Regulation.

Single-component metal halides with white light emission are highly attractive for solid-state lighting applications, but it is still challenging to develop all-inorganic lead-free metal halides with high white-light emission efficiency. Herein, by rationally introducing silver (Ag) into zero-dimensional (0D) Cs3 Cu2 Br5 as new structural building unit, a one-dimensional (1D) bimetallic halide Cs6 Cu3 AgBr10 is designed that emits strong warm-white light with an impressive photoluminescence quantum yield (PLQY) of 94.5% and excellent stability. This structural transformation lowers the conduction band minimum while maintaining the localized nature of the valence band maximum, which is crucial in expanding the excitation spectrum and obtaining efficient self-trapped excitons (STEs) emission simultaneously. Detailed spectroscopy studies reveal that the white-light originates from triplet STEs emission, which can be remarkably improved by weakening the strong electron-phonon coupling and thus suppressing phonon-induced non-radiative processes. Moreover, the interesting temperature-dependent emission behavior, together with self-absorption-free property, make Cs6 Cu3 AgBr10 as sensitive luminescent thermometer and high-performance X-ray scintillator, respectively. These findings demonstrate a general approach to achieving effective single-component white-light emitters based on lead-free, all-inorganic metal halides, thereby opening up a new avenue to explore their versatile applications such as lighting, temperature detection and X-ray imaging.

A ratiometric optical thermometer with dual-color emission based on Eu2+-doped CsCu2I3 microcrystals

With the increasing demand for non-contact fluorescence intensity ratio-based optical thermometry, novel phosphor materials with high-efficiency, dual-emitting centers, and differentiable temperature sensitivity are highly desired. In this work, rare earth Eu2+ ions were incorporated into CsCu2I3 microcrystals by solid-state reaction. Under a single UV excitation, the as-synthesized samples exhibit two emissions: 452 nm blue emission from the 5d→4f transition of Eu2+ and 582 nm yellow emission from self-trapped exciton emission of CsCu2I3. The photoluminescence quantum yield reaches to 50%. The dual-band emission of Eu2+-doped CsCu2I3 shows different temperature responses in the range of 260–360 K. Based on fluorescence intensity ratio technology, the maximum absolute sensitivity and relative sensitivity are 0.091 K–1 (at 360 K) and 2.60%/K (at 260 K), respectively. These results suggest that Eu2+-doped CsCu2I3 could be a good candidate for highly sensitive optical thermometer.

Improved optical thermometric sensitivity of Eu3+‐doped calcium niobate phosphor via nonstoichiometric control

AbstractEu3+‐doped calcium niobate CaNbxO6 phosphors were successfully prepared by a solid‐state reaction, and the crystal structure, morphology, energy transfer process, and temperature‐dependent behaviors were systematically investigated. The CaNbxO6 host matrix presents the self‐activated characteristic emission at 470 nm due to the charge transfer transition of Nb5+–O2+, and the corresponding photoluminescence intensity reaches the maximum intensity when the nonstoichiometric ratio of Ca2+/Nb5+ ions is 1:1.9. Moreover, the energy transfer process from the host (470 nm) to Eu3+ (612 nm) ions in the CaNb1.9O6:Eu3+ phosphor is demonstrated, and the corresponding energy transfer efficiency is significantly enhanced compared with that of stoichiometric sample. Furthermore, it is observed that nonstoichiometric ratio of Nb5+ ions deteriorates the thermal quenching of the matrix while guaranteeing the thermal stability of the activators, resulting in the relative sensitivity (Sr) of CaNb1.9O6:Eu3+ being greatly improved from 2.235% to 3.673% K−1. Herein, these results provide an effective strategy for manipulating the sensitivity of optical thermometers of phosphors based on the induced modulation of the temperature‐response performance via nonstoichiometric control.

Design strategies for three highly sensitive multimodal optical thermometers based on diverse luminescence thermal-response in BaLu2Si3O10:Ln3+, Yb3+ phosphors (Ln3+=Er3+, Ho3+, Nd3+)

Optical thermometer has gradually become a hotspot due to its contactless measurement, high spatial resolution and rapid response, while most of them currently used single-mode measurement without reference and calibration. Herein, three multimodal optical thermometers were designed in BaLu2Si3O10: Er3+/Ho3+/Nd3+, Yb3+ phosphors. Interestingly, both Er3+ and Ho3+ doped phosphors demonstrated thermochromic phenomenon, promising to be candidates for intelligent high-temperature alarms. Benefiting from diverse thermo-response of green and red emissions of above two phosphors, two visible two-mode optical thermometers were established by four fluorescence intensity ratio (FIR) modes. Besides, a near-infrared (NIR) multimodal optical thermometer was also proposed by three FIR modes in Nd3+-Yb3+ co-doped phosphor with continuous luminescence thermal enhancement. Because of efficient phonon-assistance energy transfer process, the 4F7/2 → 4I9/2 transition demonstrated super thermal enhancement over 2600 times. The method by integrating several independent optical addressed temperature readout modes provides diversified avenue toward the design of highly sensitive optical thermometers.

The near-infrared emission of Er3+-doped yttrium oxy-fluoride ceramic powders: Temperature reading using uncoupled and thermally coupled energy levels

The performance of Er3+-doped yttrium oxy-fluoride (YOF) powders for optical temperature sensing is examined in this paper. YOF: Er3+ ceramic powders with near-infrared fluorescent emissions were synthesized via the combustion method. After heat treatment at 800 °C, the crystalline material shows strong near-infrared (NIR) fluorescence when excited with CW laser at 808 nm. The Er3+ emission bands found in the NIR region, centered at 970 and 1526 nm, correspond to excited levels 4I11/2 and 4I13/2, which relax to the ground state 4I15/2. YOF: Er3+ fluorescent powders are used to explore the optical thermometer sensitivity in the NIR region at 980–1650 nm in the temperature range from 298 to 523 K. Under the assumption of a quasi-equilibrium Boltzmann population distribution, the temperature sensing properties of thermally linked Stark sublevels derived from (4I11/2 and 4I13/2)→ 4I15/2 transitions have been thoroughly investigated using the FIR variation readout between these thermally connected Stark sublevels. The thermal sensing performance has also been investigated based on the FIR approach between non-thermally coupled levels (NTCL). The FIR readout of 4I11/2 → 4I15/2 and 4I13/2 → 4I15/2 NTCL transitions were used to calculate the relative sensitivity in the NIR spectral range. The performance comparison of the TCL and NTCL FIR techniques reveals the possibility of this ceramic powder being employed as a ratiometric thermal sensor for remote temperature readings.

Cr3+-Doped NIR Phosphor with Well-Defined Stokes/Anti-Stokes Phonon Sidebands for a Ratiometric Thermometer and Thermally Stable NIR LEDs

Near-infrared (NIR) luminescent materials have attracted enormous attention for the cutting-edge applications in optical thermometer and NIR LEDs. Herein, we report a highly efficient Cr3+-doped NIR phosphor, BaAl4Sb2O12:0.024Cr3+ (BASO:Cr3+), with 91% internal quantum efficiency. Strikingly, BASO:Cr3+ possesses rare and typical Stokes/anti-Stokes phonon sidebands. The Stokes phonon sideband decreases with increasing temperature, while the anti-Stokes one increases considerably. Consequently, this inverse change has gifted the BASO:Cr3+ with excellent thermal stability, which maintains 118% of the room temperature emission intensity at 423 K. In addition, the well-defined Stokes/anti-Stokes phonon sidebands are applied to a ratiometric thermometer with a maximum relative sensitivity factor of 3.12% K–1 at 150 K. Finally, a well-performing NIR LED is made with BASO:Cr3+, which can be used for nondestructive testing, information encryption, and night vision. Our findings not only shed light on the emission behavior of Cr3+ but also point out an avenue for thermally stable NIR phosphors and a sensitive optical thermometer.

Tailoring Dye Emissions within Metal–Organic Frameworks for Tunable Luminescence and Ratiometric Temperature Sensing

Metal-organic frameworks (MOFs) have emerged as powerful platforms for tuning the luminescence characteristics of guests due to their various structures and functions. Tunable and stimuli-responsive luminescence of guests within MOFs can be achieved through a judicious choice of guests and hosts. Herein, we demonstrate a dramatic change in the luminescence of dye excimers encapsulated in MOFs. A polar dye presented largely red-shifted excimer emissions in MOFs with higher polarities, while a nonpolar dye showed very different excimer emissions. Interestingly, the excimer emissions tailored by the MOFs showed strong thermal quenching. Cz-Ant@ZIF-8, containing two luminescent dyes (carbazole (Cz) and anthracene (Ant)), was prepared, and it presented ratiometric temperature sensing properties (1.55% K-1) in the temperature range of 278-353 K. This work sheds light on the luminescence tuning of dyes confined in MOFs and the design of sensitive ratiometric thermometers.

Crystal formation in Eu3+ - Doped oxyfluorophosphate glass-ceramics for luminescence thermometry

Eu3+ doped-Oxyfluorophosphate glasses with a general composition 75 NaPO3 - (25-x) CaO – x CaF2 (with x ranging from 0 to 25 mol%) were prepared and their spectroscopic changes induced by the addition of fluorine and when applying a thermal treatment in order to grow crystals in the glasses were investigated. The addition of CaF2 at the expense of CaO reduces Ω2 and Ω4 parameters indicating that the Eu3+ ions are located in less covalent and well separated sites in oxyfluorophosphate glasses. An increase in the CaF2 content at the expense of CaO also leads to an increase in the absolute thermometric sensitivity from (4.2 × 10−4) K−1 to (17.6 × 10−4) K−1 at 523 K while decreasing the relative thermometric sensitivity from 3.0% to 1.4%.The heat treatment leads to the precipitation of crystals, the composition of crystal phase depends on the glass composition. For the glasses with x = 0 and 10, the thermal treatment increases Ω6 while reducing Ω4, as a result of an enhanced stiffness and reduced covalency of dopant's environment due to the precipitation of various crystals. As Ω2 remains unchanged, the Eu3+ are suspected to remain mainly in the amorphous part of the glass-ceramics in agreement with the lack of sharp peaks in the emission spectrum. For the glasses with x = 20 and 25, Ω2 increases indicating a change in the site symmetry of Eu3+ resulting from the dopant entering the CaF2 crystalline phase. Due to the changes in the Eu3+ sites in the heat treated glasses, the heat treatment of the glass increases the absolute thermal sensitivity, but reduces the relative thermal sensitivity. The oxyfluorophosphate glass-ceramic with x = 25 exhibits high absolute thermometric sensitivity compared to oxyfluorophosphate glass, but also comparatively low relative sensitivity of 0.5% K−1.

Blue-light pumped NIR emission of LaOF:Pr3+ nanorods for highly sensitive nanothermometry

Remote thermal sensing is a much-needed technology in today's world; therefore, developing highly sensitive optical thermometer probes has become a necessity. In this study, the luminescence thermometers based on Pr3+ emissions in the red and near-infrared (NIR) regions were used. LaOF:Pr3+ nanorods were synthesized via a microwave-assisted hydrothermal route. The prepared nanorods exhibited excellent photoluminescence (PL) emission in the red and NIR regions under blue laser excitation. Their PL emissions were found to be influenced by temperature, which was exploited to study the thermal sensing ability of the nanorods. Fluorescence intensity ratios (FIRs) of the red and NIR emissions were evaluated for both the thermally coupled levels and the non-thermally coupled levels. The maximum absolute and relative thermal sensitivities were 5% K−1 at 573 K and 0.8% K−1 at 303 K, respectively. The temperature resolution of 0.17 K was achieved for the FIR calculated from the NIR emissions. The nanorods passed the repeatability test, and the FIR maintained a similar pattern for repeated heating and cooling cycles. The results suggest that the prepared nanorods are promising materials for nanothermometry applications.

Stacking Lanthanide-MOF Thin Films to Yield Highly Sensitive Optical Thermometers.

Easy-to-integrate, remote read-out thermometers with fast response are of huge interest in numerous application fields. In the context of optical read-out devices, sensors based on the emission of lanthanides (Eu(III), Tb(III)) are particularly promising. Here, by using a layer-by-layer (LbL) approach in the liquid-phase epitaxy process, a series of continuous, low-thickness lanthanide-MIL-103 SURMOFs were fabricated to yield highly sensitive thermometers with optical readout. These Ln-SURMOFs exhibit remarkable temperature-sensing photoluminescence behavior, which can be read out using the naked eye. High transmittance is realized as well by precisely controlling the film thickness and the quality of these Ln-SURMOF thermometers. Moreover, we demonstrate that the thermal sensitivity can be improved in the temperature regime above 120 K, by controlling the energy transfer between Tb(III) and Eu(III). This performance is achieved by employing a sophisticated supramolecular architecture, namely MOF-on-MOF heteroepitaxy.