Sensitive Thermometer Research Articles

Ligand Effects on the Emission Characteristics of Molecular Eu(II) Luminescence Thermometers.

Discrete molecular organometallic europium(II) complexes are promising functional materials due to their ability to behave as highly sensitive band-shift luminescence thermometers. Furthering our understanding of the design principles salient to the emission behavior of such systems is important for developing them in this emerging application. To this end, a series of pseudo-C4v-symmetric organometallic europium(II) complexes bearing systematically varying ligand sets were synthesized and characterized to probe the influence of subtle structural modification on their optical properties. Opto-structural correlation analyses via variable-temperature single-crystal X-ray diffraction and photoluminescence spectroscopy reveal a remarkable variability in properties among structurally similar complexes and a convoluted dependence of the emission characteristics on the stereoelectronic properties of the ligands. A few factors of particular influence are nevertheless identified, including the distance between the europium(II) ion and the basal plane of the square-pyramidal coordination polyhedron, the presence of pendant electron density that might further interact with the excited-state 5d orbitals, and, qualitatively, the metal-ligand flexibility of the construct. These results help to elucidate principles that govern the luminescence properties of organometallic europium(II) complexes with an eye to enabling the rational design of high-performance luminescence thermometers of this genre.

Highly Sensitive Solid Ratiometric Luminescent Thermometer Based on N,C-Chelating Four-Coordinate Organoboron Compounds.

Realizing ratiometric thermometers using single-component organic solid-state luminophores is attractive but challenging. Here, we synthesized a series of N,C-chelated tetra-coordinated organoboron compounds and characterized their structures. Among them, sample BN2Br can be used as a luminescent thermometer and exhibits a high temperature sensitivity (3.67% K-1), a wide response range of 120-280 K, and good reversibility, which is mainly due to the temperature-dependent intermolecular stacking effect in the solid state. The proposed ratiometric thermometry protocol may provide new insights for developing photonic thermometers.

Fluorescence temperature dependent behaviors of Eu3+/Mn4+ co-doping cubic and hexagonal ZnO-TiO2 compounds: Application in high sensitive optical thermometers

ZnTiO3:Eu3+,Mn4+ phosphors with hexagonal and cubic structure are synthesized by solvothermal method. The structure of ZnTiO3 depends on precursors and the annealing temperature. Inverse spinel Zn2TiO4 phase reveals the highest thermostability compared with cubic ZnTiO3 and hexagonal ZnTiO3 phases. The different phases of ZnTiO3 crystals exhibit different photoluminescence properties. The forbidden transition of 4A2g→2T2g for Mn4+ is observed in Zn2TiO4 and hexagonal ZnTiO3 (h-ZnTiO3) due to the decreased symmetry. The zero photon line (ZPL) assigned to 2Eg→4A2g transition of Mn4+ is absent in all type ZnTiO3 phases. A sharp emission peak at 714 nm assigned to ν6 (Stokes emission) mode of Mn4+ in h-ZnTiO3 is present when the temperature was below 270 K, and increases sharply in intensity with the temperature decreasing. The similar PL spectra of cubic ZnTiO3 and Zn2TiO4 co-doped with Eu3+ and Mn4+ show a wide emission band composed of Stokes and anti-Stokes modes. The calculated nephelauxetic parameter increases from 0.84 to 1.03 and 1.18 for Mn4+ in h-ZnTiO3, cubic ZnTiO3 and Zn2TiO4, respectively, indicating the covalency decreasing, which causes the red shift of ZPL in h-ZnTiO3. The Mn4+ emissions show stronger temperature dependence than that of Eu3+, especially for that in h-ZnTiO3 matrix. Based on the fluorescence intensity ratio between IEu3+ and IMn4+, the highest relative temperature sensitivity of 2.46 %K−1 is observed in cubic ZnTiO3 (c-ZnTiO3) and Zn2TiO4. Under the excitation at 550 nm, the highest relative sensitivity of 2.9 %K−1 is achieved in c- and h-ZnTiO3 mixed phases.

Multimodal Temperature Readout Boosts the Performance of CuInS2/ZnS Quantum Dot Nanothermometers.

Fluorescent nanothermometers are positioned to revolutionize research into cell functions and provide strategies for early diagnostics. Fluorescent nanostructures hold particular promise to fulfill this potential if nontoxic, stable varieties allowing for precise temperature measurement with high thermal sensitivities can be fabricated. In this work, we investigate the performance of micelle-encapsulated CuInS2/ZnS core/shell colloidal quantum dots (QDs) as fluorescent nanothermometers. We demonstrate four temperature readout modes, which are based on variations in the photoluminescence intensity, energy, and lifetime and on a specific ratio of excitation efficiencies. We further leverage this multimodal readout to construct a fifth, multiparametric thermometer calibration based on the multiple linear regression (MLR) model. We show that the MLR approach boosts the thermometer sensitivity by up to 7-fold while reducing the readout error by about a factor of 3. As a result, our QDs offer the highest sensitivities among semiconducting QDs emitting in the first biological window. The obtained results indicate that CuInS2/ZnS QDs are excellent candidates for intracellular in vivo thermometry and provide guidelines for further optimization of their performance.

Supernormal Temperature Sensing Performance Realized through the Blue Emitting Level of Er3+ along with Detection Ability in Deep Tissues.

Fluorescence intensity ratio (FIR)-type optical thermometers based on thermally coupled energy levels (TCLs) of rare earth ions are suitable candidates for noncontact temperature detection in living organisms, microelectronics apparatus, and so forth. Therefore, the improvement of the thermometric sensitivity of TCL-based thermometers has become a research hotspot in recent years. Herein, ultrahigh sensitivity and outstanding resolution for temperature sensing have been realized in YNbO4: Yb3+/Er3+. Unusually, the thermally coupled three-level system of Er3+: 4F7/2/2H11/2/4S3/2 is first employed for optical thermometry based on FIR technology. A supernormal thermometric sensitivity of 2.67% K-1 is obtained from the thermally coupled 4F7/2 and 4S3/2 states due to the large energy gap between them, significantly surpassing that of most temperature sensors in the same category. Furthermore, the existence of the intermediate level 2H11/2 can effectively prevent the decoupling effect between 4F7/2 and 4S3/2. Additionally, the temperature sensing behavior realized by the Stark sublevels of the Er3+: 4I13/2 → 4I15/2 transition, with a penetration depth of 8 mm, shows the potential of temperature measurement in deep biological tissues, benefiting from its excitation and emission wavelengths located in the biological window. All of the data reveal that YNbO4: Yb3+/Er3+ is an ultrasensitive optical thermometer and exhibits the capacity of temperature detection in deep tissues.

Research on optical performance of Ln2O2S:Er3+/Yb3+ (Ln = La/Gd/Y) phosphors based on different phonon energies.

It is crucial to explore the intrinsic mechanisms that influence thermometric sensitivity. This study investigates the optical performance of materials with the same crystal structure but different phonon energies. Ln2O2S:Er3+/Yb3+ (Ln = La/Gd/Y) phosphors with similar morphology and particle sizes were prepared to systematically study the influence of different phonon energy matrices on optical properties. The intrinsic mechanism was elucidated through the matching degree between the energy gap and phonon energy, Judd-Ofelt (J-O) theory, and quantum dielectric theory. It was ultimately concluded that the combination of high phonon energy with a large Ω2 and a small Ω6 is beneficial for enhancing the sensitivity of temperature sensing materials.

Harnessing coherence generation for precision single- and two-qubit quantum thermometry

Quantum probes, such as single- and two-qubit probes, can accurately measure the temperature of a bosonic bath. The current investigation assesses the precision of the temperature estimate by using quantum Fisher information and the accompanying quantum signal-to-noise ratio. Employing an ancilla as a mediator between the probe and the bath improves thermometric sensitivity by transmitting temperature information into the probe qubit's coherences. In addition, we analyze two interacting qubits that were initially entangled or separated as quantum probes for various environmental configurations. Our findings show that increased precision is gained when the probe approaches its steady state, which is determined by the coupling between the two qubits. Furthermore, we can obtain high-efficiency temperature estimation for any low temperature by changing the interaction between the two qubits. Published by the American Physical Society 2024

Modeling of a Single-Band-Ratiometric Sensor Based on Lattice Positive Thermal Expansion in Eu3+-Activated Halide Perovskite Cs2NaEuCl6.

Recently, single-band ratiometric (SBR) thermometry has emerged as an innovative approach to traditional fluorescence thermometry, overcoming uncertainties associated with emission spectrum overlap or scattering while maintaining high spatial resolution and remote monitoring. This paper presents a novel Cs2NaEuCl6 perovskite prepared through a slow-cooling solution method. Additionally, it proposes a temperature sensor model that relies on the thermal quenching of charge-transfer state absorption. Mechanical studies highlight the role of lattice positive thermal expansion in affecting Eu3+ emission. Conversely, a significant emission enhancement is observed upon excitation corresponding to both the ground state and excited state absorption. The distinct luminescent behavior of this Eu3+-activated halide perovskite model makes it suitable for developing a highly sensitive SBR-type sensor with a relative sensitivity (Sr) exceeding 1.5% K-1 and temperature resolution (𝛿T) below 1 K at room temperature. Furthermore, it demonstrates the thermal stability during multiple heating-cooling cycles. Finally, the practical applicability of the proposed SBR model is demonstrated by employing a self-manufactured film sensor that enables precise real-time temperature detection for electronic components. The work is regarded as a significant stride toward the development of cutting-edge and exquisitely sensitive thermometers based on lanthanide-based halide double perovskites.

Highly sensitive optical thermometer based on Li+-doped erbium ytterbium silicate films

This work provides a new material, Li+-doped erbium ytterbium silicate, with reliable and high temperature sensing sensitivity for optical thermometers. The Li+-doped erbium ytterbium silicate films were prepared by RF magnetron sputtering. The film shows strong green visible emission, which is related to the radiation transitions from thermally coupled energy levels 2H11/2, 4S3/2 to 4I15/2. Lithium doping reduces the field symmetry around erbium and improves the radiation transition efficiency, and Yb doping improves the pump light absorption. Lithium or ytterbium is advantageous to enhance up-conversion luminescence and temperature sensing sensitivity of erbium ions. Therefore, the temperature dependence of green up-conversion luminescence in the range of 80–460 K of the Li+-doped erbium ytterbium silicate films have been found to be a promising optical thermometer material with a high relative sensitivity of 16.9 % K−1, which is higher than the optimum value of other Er3+ materials. In addition, we have provided a preliminary temperature measurement scheme based on the Li+-doped erbium ytterbium silicate film.

Boosted sensitive optical thermometers utilizing synergistic effects of thermal enhancement and quenching in Er/Yb/Nd triply-doped Bi4Ti3O12 nanosheets

Rare earth-doped nanomaterials can achieve diverse upconversion luminescence by changing doping ions, presenting them as promising candidates for rapid temperature measurement. However, most upconversion luminescent phosphors have a thermal quenching effect, which greatly weakens the luminous intensity of the material and impairs thermometry performances. Here, we studied the synthesis of Bi4Ti3O12 nanosheets tridoped with Er3+, Yb3+, and Nd3+ ions using molten salt method. Notably, this luminescent material demonstrates both thermal quenching and thermal enhancement effects. The unusual phenomenon results in a high sensitivity of the optical temperature sensor based on the inter-ion energy level between Er3+ and Nd3+. At 523 K, this sensitivity reaches 5.94×10−2 K−1, surpassing that of sensors relying on the thermal coupling of only Er3+ ions by nearly ninefold. Our findings suggest a promising strategy to augment the temperature sensing sensitivity of luminescent materials, paving the way for potential applications in precise temperature monitoring.

High sensitive ratiometric optical thermometer based on different multi-photon processes of upconversion luminescence in scheelite Ca1-xMgxWO4:Er3+/Yb3+ phosphors

The relative fluorescence intensity from different multi-photon processes is affected by the excitation light source fluctuation, which reduces the anti-interference and sensitivity of thermometers based on fluorescence intensity ratio (FIR) in upconversion (UC) luminescence. Ca1-xMgxWO4: Yb3+, Er3+ phosphors with scheelite structure were synthesized to investigate their anti-interference and higher temperature sensitivity. With x increasing from 0 to 1, the Bragg angle shifted toward higher angle, indicating that the larger disorders were introduced into the phosphors. The emissions assigned to Er3+ were enhanced with Mg2+ concentration increasing, attributed to oxygen vacancies according to the results of electron paramagnetic resonance. The photon numbers of upconversion luminescence assigned to 2H11/2 → 4I15/2, 4S3/2 → 4I15/2 and 4F9/2 → 4I15/2 transitions of Er3+ were three- and two-photon processes, respectively. The ratio between the cube of 4S3/2 and the square of 2H11/2 emissions revealed higher temperature sensing performance and anti-interference on the excitation source power than the that between 4S3/2 and 2H11/2. The maximum relative sensitivity was 0.66 % K−1 at 300 K based on the common optical ratiometric thermometry. The maximum relative sensitivity based on the emissions assigned to different multi-photon processes was 7.2 % K−1 at 573 K. The dopants of Mg2+ composited of oxygen vacancies in CaWO4 crystals improved the luminous intensity and temperature sensing performance. This suggested the potential application of optical ratiometric thermometers based on different multi-photons of UC luminescence in temperature sensing field.

“Pseudo-TCELs” of Tm3+ induced ultra-highly sensitive fluorescence thermometers with adjacent emission peaks

Up to now, fluorescence thermometers based on fluorescence intensity ratio (FIR) technology is difficult to meet high sensitivity and short recording wavelength range simultaneously. In this work, Tm3+/Yb3+ co-doped oxyfluoride glass ceramics (GCs) were synthesized via melting-quenching method and subsequent thermal treatment. Well-crystallized Tm3+/Yb3+ co-doped fluoride nanocrystals (NCs) have formed in the oxide glass matrix. UCL properties of Tm3+/Yb3+ co-doped oxyfluoride GCs under excitation of 976 nm laser at room temperature (RT) were measured and studied, in which an unusual emission at 724 nm originated from 1D2→3F2,3 transition was recorded for the first time. Besides, temperature measurements capable of Tm3+/Yb3+ co-doped oxyfluoride GCs was studied and ultra-high sensitivity and short recording wavelength range were achieved simultaneously based on “pseudo-TCELs” of Tm3+. The maximum Sr and Sa were obtained based on the “pseudo-TCELs” of Tm3+, 3F2,3→3H6 (I680 nm+700 nm)/1D2→3F2,3 (I724 nm), as values of 4.17% K−1 at 288 K and 13.95% K−1 at 498 K, which broke the limitation of ΔE on thermosensitivity and were significantly higher than existing luminescent thermometers. Moreover, the value of Sr based on the “pseudo-TCELs” of Tm3+ maintained larger than 1.12%K−1 in high temperature range of 350–500 K without obvious descending, superior to most previous reports. The “pseudo-TCELs” of Tm3+ provides a new strategy for obtaining high sensitivity based on adjacent emission peaks and short recording wavelength range simultaneously, contributing to significantly improve the quality and efficiency of temperature detection.

Experimental setup for thermal measurements at the nanoscale using a SThM probe with niobium nitride thermometer.

Scanning Thermal Microscopy (SThM) has become an important measurement technique for characterizing the thermal properties of materials at the nanometer scale. This technique requires a SThM probe that combines an Atomic Force Microscopy (AFM) probe and a very sensitive resistive thermometer; the thermometer being located at the apex of the probe tip allows for the mapping of temperature or thermal properties of nanostructured materials with very high spatial resolution. The high interest of the SThM technique in the field of thermal nanoscience currently suffers from a low temperature sensitivity despite its high spatial resolution. To address this challenge, we developed a high vacuum-based AFM system hosting a highly sensitive niobium nitride (NbN) SThM probe to demonstrate its unique performance. As a proof of concept, we utilized this custom-built system to carry out thermal measurements using the 3ω method. By measuring the V3ω voltage on the NbN resistive thermometer under vacuum conditions, we were able to determine the SThM probe's thermal conductance and thermal time constant. The performance of the probe is demonstrated by performing thermal measurements in-contact with a sapphire sample.

A highly sensitive multiple-mode optical thermometer designed in Eu 2+/3+ and Li + co-doped polymorphism compound LaSc 3(BO 3) 4

A highly sensitive multiple-mode optical thermometer designed in Eu ^2+/3+ and Li ⁺ co-doped polymorphism compound LaSc ₃(BO ₃) ₄

Dy3+,Mn4+ co-doped phosphors for synergistic luminescent dual-mode thermometer and high-resolution imaging

Fluorescent temperature measurement has become a research hotspot due to its characteristics of non-contact, miniaturization, and fast response. However, it remains a key challenge to realize excellent sensitivity and high resolution. Herein, a series of La2MgTiO6:Dy3+,Mn4+ phosphors are developed and the related energy transfer between Dy3+→Mn4+ is discovered. The coupling distance between Mn4+ and adjacent ligands is greatly affected by temperature. However, the energy differences between the emission energy levels and lower energy levels of Dy3+ hinder the multi-phonon relaxation process, which moderates the thermal quenching rate of Dy3+. Therefore, highly sensitive FIR thermometers are built according to the significant discrimination temperature dependence of Dy3+ and Mn4+. The maximum Sa and Sr reach 0.022 K−1(@563 K) and 2.622 %K−1(@544 K). In contrast, a thermometer based on the emission lifetime of Mn4+ is fabricated, which is extremely sensitive to temperature. Interestingly, Dy3+ can effectively promote the quenching of Mn4+, and then improve the sensitivity. The maximum Sr enhances from 1.621 %K−1(@503 K) to 2.305 %K−1 (@480 K). The high sensitivity and resolution of the dual-mode fluorescence thermometry have exceeded most of the current optical thermal measurement materials. Besides, the thermochromic properties presented by the designed phosphors can be combined with PDMS films to qualitatively evaluate the ambient temperature.

Obtaining versatile Cr3+-activated phosphors with improved far-red emissions via host composition modulation

Cr3+-activated spinel-type phosphors have great potential in different application scenes due to their unique sharp and far-red (FR) emission. However, the multi-functionalization of these phosphors is still limited by their unsatisfied comprehensive properties. Herein, a simple composition engineering was used to explore versatile phosphors, using Ga3+ to substitute Al3+ to improve the optical performances of spinel LiAl5–xGaxO8:Cr3+. The substitution of Ga3+ evidently affects the crystal field environment of Cr3+ and further accounts for the luminescence optimization. Using the optimized phosphor, two sensitive thermometers based on fluorescence intensity ratio (FIR) technique were explored on account of the different temperature dependencies of 4T2→4A2 and 2E→4A2 emission and of R2 and R1 emission. The maximum relative sensitivity Sr are 1.29%/K at 323 K and 1.94%/K at 298 K, respectively, which are superior to that of the Ga3+-unsubstituted one. Besides, the Ga3+→Al3+ substitutions endow the resultant phosphors with larger atomic number (Zeff) and theoretical density, which is more conducive to improving X-ray-stimulated emission for X-ray detection. Finally, the potential applications of the developed phosphor are also reflected in plant growth and night vision surveillance, as it is shown to be capable of matching with the absorption of phytochrome PFR and visualizing objects in the dark. This contribution not only proves that the developed LiAl5–xGaxO8:Cr3+ FR phosphors are promising versatile platforms, but also provides an essential guidance for designing more novel multi-functional materials.

Tunable and highly sensitive fluorescent thermometers from La2CaZrO6:Cr3+ with a time-resolved technology.

Non-contact optical temperature measurement can effectively avoid the disadvantages of traditional contact thermometry and thus, become a hot research topic. Herein, a fluorescence intensity ratio (FIR) thermometry using a time-resolved technique based on La2CaZrO6:Cr3+ (LCZO) is proposed, with a maximum relative sensitivity (Sr - FIR) of 2.56% K-1 at 473 K and a minimum temperature resolution of 0.099 K. Moreover, the relative sensitivity and temperature resolution can be effectively controlled by adjusting the width of the time gate based on the time-resolved technique. Our work provides, to our knowledge, new viewpoints into the development of novel optical thermometers with adjustable relative sensitivity and temperature resolution on an as-needed basis.

Upconversion Luminescence Properties and Temperature Sensing Characteristics of Tm3+, Yb3+-codoped SrAl2Si2O8 Phosphors with High Thermometric Sensitivities

In this paper, a SrAl2Si2O8:Tm3+,Yb3+ upconversion (UC) phosphor was prepared with a high-temperature solid-phase method, and proved that the strontium feldspar structure was an excellent UC matrix. The Tm3+ were shown to have a maximum relative thermometric sensitivity (Sr) of 1.67% K−1 at 298 K and a maximum absolute thermometric sensitivity (Sa) of 1.34% K−1 at 573 K. The non-thermally coupled energy level corresponded to the maximum relative thermometry sensitivity (Sr) of 2.4% K−1 at 298 K and a maximum absolute sensitivity (Sa) of 13% K−1 at 423 K. The use of the fluorescence intensity ratio of the nonthermally coupled energy levels of Tm3+ for temperature measurements improved the temperature measurement sensitivity of the same material. These results indicated that the phosphor has good temperature sensing performance with a wide sensing range and good stability and has potential thermometry applications in the first biological window.

Sensitive Thermochromic Behavior of InSeI, a Highly Anisotropic and Tubular 1D van der Waals Crystal.

Thermochromism, the change in color of a material with temperature, is the fundamental basis of optical thermometry. A longstanding challenge in realizing sensitive optical thermometers for widespread use is identifying materials with pronounced thermometric optical performance in the visible range. Herein, it is demonstrated that single crystals of indium selenium iodide (InSeI), a 1D van der Waals (vdW) solid consisting of weakly bound helical chains, exhibit considerable visible range thermochromism. A strong temperature-dependent optical band edge absorption shift ranging from 450 to 530 nm (2.8 to 2.3 eV) over a 380 K temperature range with an experimental (dEg/dT)max value extracted to be 1.26 × 10-3 eV K-1 is shown. This value lies appreciably above most dense conventional semiconductors in the visible range and is comparable to soft lattice solids. The authors further seek to understand the origin of this unusually sensitive thermochromic behavior and find that it arises from strong electron-phonon interactions and anharmonic phonons that significantly broaden band edges and lower the Eg with increasing temperature. The identification of structural signatures resulting in sensitive thermochromism in 1D vdW crystals opens avenues in discovering low-dimensional solids with strong temperature-dependent optical responses across broad spectral windows, dimensionalities, and size regimes.

Constructing [2.2]Paracyclophane‐Based Ultrasensitive Optical Fluorescent‐Phosphorescent Thermometer with Cucurbit[8]uril Supramolecular Assembly

AbstractThe pursuit of developing novel approaches to fully organic and efficient phosphorescent materials is in high demand. The optical activity of such functional, organic phosphorescent/fluorescent materials may exhibit great temperature dependence, allowing their application as advanced, highly sensitive molecular thermometers. In this study, a rational strategy involving host–guest complexation and polymerization of [2.2]paracyclophane (PCP) based molecules with cucurbit[8]uril (CB8) to suppress the molecular motion and promote temperature‐dependent phosphorescence is presented. The rigid cavity of CB8 provides an ideal microenvironment to host PCP molecules 1 and 2, significantly enhancing the photophysical performance after complexation. Co‐polymerizing phosphors 1 and 2 with acrylamide is an efficient method for improving phosphorescence. Incorporating CB8 into the resulting P‐1 and P‐2 polymers enhances phosphorescence performance. Importantly, the obtained materials exhibit a big structure‐dependent spectral shift and change of phosphorescence lifetimes with temperature, allowing novel, phosphorescence‐based, and purely organic optical thermometers to be developed. The practical applications of PCP‐based luminescent materials in temperature sensing via a multi‐parameter approach are showcased, i.e., using fluorescence spectral shift and changes in bandwidth, as well as phosphorescence lifetimes, exhibiting thermal sensitivity of ≈17.7 cm−1 °C−1, 47.8 cm−1 °C, and 5.2% °C−1, respectively.