Highly Sensitive Dual-Phase Nanoglass-Ceramics Self-Calibrated Optical Thermometer

A Study on Miniaturized In-Situ Self-Calibrated Thermometers Based on Ga and Ga-Zn Fixed Points

In order to ensure the reliability and accuracy of long-term temperature measurement where the thermometers are discommodious or even impossible to access for conventional periodical calibration, a study on miniaturized in-situ self-calibrated (MISSC) thermometers based on Ga and Ga-Zn fixed points was conducted using temperature scale transfer technology. One MISSC thermometer consists of three parts: the first is the fixed-points hardware, including a container with two cells separately filled with Ga and Ga-Zn; the second is the temperature sensing hardware, made of a Type T thermocouple; the third is the mini-power heating hardware, made of a film resistance. The measurement and calibration (M&C) system comprises a temperature measurement and data processing subsystem and a mini-power heating control subsystem. Then, an in-situ self-calibration can be carried out by mini-power heating from a room temperature of about 20 °C, and then by comparison between the measured phase transition plateau results and the standard fixed-points, i.e., Ga fixed point (about 29.76 °C) and Ga-Zn fixed point (about 25.20 °C). A series of experiments were performed, and the results show that: (1) both the proposed hardware design and the self-calibration method are feasible, and (2) the Φ16 mm × 25 mm MISSC thermometer is found to be the most miniaturized one that can realize reliable self-calibration in this study.

Eu3+ doped CaWO4 nanophosphor for high sensitivity optical thermometry

Eu3+ doped calcium tungstate phosphors were obtained by using sodium citrate as chelating agent in hydrothermal process. The structure and morphology of the samples were indicated by XRD and the FE-SEM. The samples prepared by us are scheelite structure. In addition, the particle size of sample decreases with sodium citrate dosage increasing, and finally reaches the nanoscale. The average particle size is 90 nm. The temperature measurement properties of phosphors were tested. It can be seen from test results that the thermal quenching behavior of Eu3+ and WO42- luminescence has obvious difference. Hence, the FIR of Eu3+ and WO42- can be used to express temperature. The maximum relative sensitivity increases with the decrease of particle size and the maximum is 4.3% K-1 (303 K, 90 nm). Moreover, the color of sample luminescence altered continuously from blue to pink-red as the temperature increased. The luminous color of the sample can be used to roughly estimate the temperature. Therefore, the CaWO4: Eu3+ nanophosphor are promising materials for optical thermometry.

Boltzmann relation reliability in optical temperature sensing based on upconversion studies of Er3+ /Yb3+ codoped PZT ceramics

The fluorescence intensity ratio (FIR) of two thermally coupled levels with temperature follows the Boltzmann equation and shows an exponential nature to the temperature which is purely dependent on the energy difference between the levels. Despite the identical energy difference between the thermally coupled levels, researchers have observed varying sensitivities for various samples. In this article, the FIR and sensitivities were calculated using the Boltzmann equation by changing various parameters such as energy difference (ΔE) and the value of the constant C. The results were compared with various reports for Er³⁺ /Yb³⁺ ions. After analysis, a new polynomial fit equation was used to determine the temperature sensitivities for the Er³⁺ /Yb³⁺ codoped PbZrTiO₃ phosphor in lieu of the conventional Boltzmann equation. The polynomial fit equation eliminated the dependency of the sensitivity on the inverse of the FIR factor and a flat sensitivity curve was obtained with temperature.

Synthesis of core–shell nanoparticles based on interfacial energy transfer for red emission and highly sensitive temperature sensing

Highly efficient red up-conversion luminescence is achieved by constructing a core–shell structure of NaYF4:Er3+,Tm3+@NaYF4:Yb3+ based on the interfacial energy transfer process.

Fluorescence Thermometer: Intermediation of the Fontal Temperature and Light

The rapid advance of thermal materials and fluorescence spectroscopy has extensively promoted micro-scale fluorescence thermometry development in recent years. Based on the advantages of fast response, high sensitivity, simple operation,...

Luminescence intensity ratio thermometry based on combined ground and excited states absorptions of Tb3+ doped CaWO4

Luminescence intensity ratio (LIR) thermometry is of great interest, because of its wide applications of noninvasive temperature sensing. Here, a LIR thermometry based on combined ground and excited states absorptions is developed using CaWO₄:Tb³⁺. The ratio of single luminescence (⁵D₄-⁷F₅) intensities under 379 and 413 nm excitations with opposite temperature dependences, attributed to the thermal coupling of ground state ⁷F₆ and excited state ⁷F₅, is used to measure temperature. This LIR method achieves a high relative sensitivity of 2.8% K^-1, and can avoid complex spectral splitting by collecting all down-shifting luminescence bands, being a promising accurate luminescence thermometry.

Integrating Positive and Negative Thermal Quenching Effect for Ultrasensitive Ratiometric Temperature Sensing and Anti-counterfeiting

Fluorescence intensity ratio-based temperature sensing with a self-referencing characteristic is highly demanded for reliable and accurate sensing. Although enormous efforts have been devoted to explore high-performance luminescent temperature probes, it remains a daunting challenge to achieve highly relative sensitivity which determines temperature resolution. Herein, we employ a novel strategy to achieve temperature probes with ultrahigh relative sensitivity through integrating both positive and negative thermal quenching effect into a hydrogel. Specifically, Er³⁺ ions show evidently a positive thermal quenching effect in Yb/Er:NaYF₄@NaYF₄ nanocrystals while Nd³⁺ and Tm³⁺ ions in a Yb₂W₃O₁₂ bulk exhibit prominently a negative thermal quenching effect. With elevating temperature from 313 to 553 K, the fluorescence intensity ratio of Er (540 nm) to Nd (799 nm) and Tm (796 nm) to Er (540 nm) is significantly decreased about 1654 times and increased about 14,422 times, respectively. The maximum relative sensitivity of 15.3% K^-1 at 553 K and 23.84% K^-1 at 380 K are achieved. The strategy developed in this work sheds light on highly sensitive probes using lanthanide ion-doped materials.

Simultaneous Tailoring of Dual-Phase Fluoride Precipitation and Dopant Distribution in Glass to Control Upconverting Luminescence

In situ glass crystallization is an effective strategy to integrate lanthanide-doped upconversion nanocrystals into amorphous glass, leading to new hybrid materials and offering an unexploited way to study light-particle interactions. However, the precipitation of Sc³⁺-based nanocrystals from glass is rarely reported and the incorporation of lanthanide activators into the Sc³⁺-based crystalline lattice is formidably difficult owing to their large radius mismatch. Herein, it is demonstrated that lanthanide dopants with smaller ionic radii can act as nucleating agents to promote the nucleation/growth of KSc₂F₇ nanocrystals in oxyfluoride aluminosilicate glass. A series of structural and spectroscopic characterizations indicate that Ln-dopant-induced K/Sc/Ln/F amorphous phase separation from glass is an essential prerequisite for the precipitation of KSc₂F₇ and the partition of Ln dopants into the KSc₂F₇ lattice by substituting Sc³⁺ ions. Importantly, modifying the Ln-to-Sc ratio in glass enables to control competitive crystallization of KSc₂F₇ and Ln-based (KYb₂F₇, KLu₂F₇, and KYF₄) nanocrystals and produce dual-phase fluoride-embedded nanocomposites with distinct crystal fields. Consequently, tunable multicolor upconversion luminescence can be achieved through diversified regulatory approaches, such as adjustment of the dual-phase ratio, selective separation of Ln³⁺ dopants, and alteration of incident pumping laser. As a proof-of-concept experiment, the application of dual-phase glass as a color converter in 980 nm laser-driven upconverting lighting is demonstrated.

Sensors for optical thermometry based on luminescence from layered YVO4: Ln3+ (Ln = Nd, Sm, Eu, Dy, Ho, Er, Tm, Yb) thin films made by atomic layer deposition

Below the Earth’s crust, temperatures may reach beyond 600 K, impeding the batteries used to power conventional thermometers. Fluorescence intensity ratio based temperature probes can be used with optical fibers that can withstand these conditions. However, the probes tend to exhibit narrow operating ranges and poor sensitivity above 400 K. In this study, we have investigated single and dual layered YVO₄: Ln³⁺ (Ln = Nd, Sm, Eu, Dy, Ho, Er, Tm, Yb) thin films (100–150 nm) for use in fluorescence intensity ratio based temperature sensors in the 300–850 K range. The type of lanthanide emission can be fine-tuned by adjusting the thickness of each layer, and the layered structure allows for emission from otherwise incompatible lanthanide pairs. This novel multi-layered approach enables high sensitivity over a broad temperature range. The highest relative sensitivity was achieved for a dual layered YVO₄: Eu³⁺/YVO₄: Dy³⁺ sample, exhibiting a maximum sensitivity of 3.6% K⁻¹ at 640 K. The films were successfully deposited on all tested substrates (silicon, iron, aluminum, glass, quartz, and steel), and can be applied homogenously to most surfaces without the use of binders. The films are unaffected by water, enabling non-contact temperature sensing in water, where IR thermometers are not an option.

Multifunctional Optical Thermometry Based on the Rare-Earth-Ions-Doped Up-/Down-Conversion Ba2TiGe2O8:Ln (Ln = Eu3+/ Er3+/ Ho3+/ Yb3+) Phosphors

The fabrication of a multifunctional sensor together with a widening temperature-sensing range is an essential challenge in optical thermometers especially for trivalent lanthanide-doped materials. Herein, we design a wide range, highly sensitive, and multifunctional thermometer by exploiting the emission spectrum of Eu³⁺ ions, and further detailed discussion has been made on the new temperature-sensing mechanism. The sensor can be operated between 358 and 548 K with a maximum relative sensitivity ( S_r) of 0.93% K^-1 at 358 K, which is higher than that of most temperature-sensing materials. A paramount superiority is that the calibration parameter can be directly calculated from the single Eu³⁺ emission spectrum, avoiding the demand of other calibrations, which realizes the coexistence of a simple structure and high precision. Furthermore, other up-conversion thermometers based on Er³⁺/Ho³⁺/Yb³⁺ co-doped Ba₂TiGe₂O₈ (BTG) phosphors as well as the down-conversion thermometer based on Eu³⁺-doped Ba₂TiGe₂O₈ (BTG:Eu³⁺) phosphor have been synthesized for comparison, and the results show that the novel thermometer (BTG:Eu³⁺) has a much higher sensitivity than that of the traditional thermometers (BTG:Er³⁺/Ho³⁺/Yb³⁺). In addition, the versatility of the phosphor (BTG:Eu³⁺) is simultaneously reflected in its applications to red phosphor for white-light emitting diodes (W-LEDs) and plant growth lamps. All of the results suggest that BTG:Eu³⁺ could be a good candidate with its highly sensitive S_r value for optical thermometry and as a safety sign in high-temperature environments.

A self-calibrated luminescent thermometer based on nanodiamond-Eu/Tb hybrid materials

ND-PMA-RE was synthesized and the ND-PMA-Eu/Tb could be served as a self-referencing luminescent thermometer due to the temperature-dependent luminescence performance.

Highly efficient red-emitting Ca2YSbO6:Eu3+ double perovskite phosphors for warm WLEDs

A double perovskite Ca₂YSbO₆:Eu³⁺ red-emitting phosphor with high concentration quenching and excellent quantum efficiency was developed to find a potential application in warm WLEDs.

Optical differential temperature measurement with beat frequency phase fluorometry

We present, to the best of our knowledge, a new method for differential temperature measurement based on thermal sensitivity of the fluorescence lifetime of thermographic phosphors. Pairs of thermographic phosphors are excited with intensity-modulated light at frequencies ω and ω+Δω. The phase shift Δθ of the summary fluorescence intensity beat signal envelope is measured. A prototype of a fluorometric differential temperature sensor is developed, and feasibility of the method is experimentally demonstrated with a Sm²⁺:SrFCl crystal and the D₁5->F7₀ transition for high thermal sensitivity. The observed linear dependence between envelope phase shift Δθ and temperature difference ΔT agrees with the theoretical prediction. Sensitivity of S=-0.97°/°C was achieved. This method could also be applied to differential measurements of any parameter affecting fluorescence lifetime.

A luminescent Lanthanide-free MOF nanohybrid for highly sensitive ratiometric temperature sensing in physiological range

Luminescent MOF materials with tunable emissions and energy/charge transfer processes have been extensively explored as ratiometric temperature sensors. However, most of the ratiometric MOF thermometers reported thus far are based on the MOFs containing photoactive lanthanides, which are potentially facing cost issue and serious supply shortage. Here, we present a ratiometric luminescent thermometer based on a dual-emitting lanthanide-free MOF hybrid, which is developed by encapsulation of a fluorescent dye into a robust nanocrystalline zirconium-based MOF through a one-pot synthesis approach. The structure and morphology of the hybrid product was characterized by Powder X-ray diffraction (PXRD), N₂ adsorption-desorption measurement and Scanning electron microscopy (SEM). The pore confinement effect well isolates the guest dye molecules and therefore suppresses the nonradiative energy transfer process between dye molecules. The incorporated dye emission is mainly sensitized by the organic linkers within MOF through fluorescence resonance energy transfer. The ratiometric luminescence of the MOF hybrid shows a significant response to temperature due to the thermal-related back energy transfer process from dye molecules and organic linkers, thus can be exploited for self-calibrated temperature sensing. The maximum thermometric sensitivity is 1.19% °C^-1 in the physiological temperature range, which is among the highest for the ratiomtric MOF thermometers that operating in 25-45°C. The temperature resolution is better than 0.1°C over the entire operative range (20-60°C). By integrating the advantages of excellent stability, nanoscale nature, and high sensitivity and precision in the physiological temperature range, this dye@MOF hybrid might have potential application in biomedical diagnosis. What' more, this work has expanded the possibility of non-lanthanide luminescent MOF materials for the development of ratiometric temperature sensors.

Relative sensitivity variation law in the field of fluorescence intensity ratio thermometry

We study the variation law of relative sensitivity in the field of fluorescence intensity ratio thermometry. It is theoretically demonstrated that there must be only one maximum value of relative sensitivity in the case in which there is a positive offset in fitting function. Moreover, the method to obtain this maximum is proposed. Experimental results, taking the D₁5/D5₀ levels of Eu³⁺ as examples, are in excellent accordance with the conclusion. The mechanism behind is then investigated, and other populating processes imposed on the D₁5 level, which exert negative outcome on thermal sensitivity, are found to play a key role in determination of this unique variation law.

Novel highly efficient single-component multi-peak emitting aluminosilicate phosphors co-activated with Ce3+, Tb3+ and Eu2+: luminescence properties, tunable color, and thermal properties

Single-composition multicolor luminescence and warm white light emission are realized, which are applied to solid lighting and ratiometric temperature sensing.

Self-calibrated optical thermometer LuNbO4:Pr3+/Tb3+ based on intervalence charge transfer transitions

High sensitivity thermometer LuNbO₄:Pr³⁺/Tb³⁺ based on intervalence charge transfer transitions.

Investigation of photoluminescence properties, Judd–Ofelt analysis, luminescence nanothermometry and optical heating behaviour of Er3+/Eu3+/Yb3+:NaZnPO4 nanophosphors

The Er³⁺/Eu³⁺/Yb³⁺:NaZnPO₄ nanophosphors can be used as temperature sensors and optical nano-heaters with significant sensor sensitivity.

Understanding differences in Er3+–Yb3+ codoped glass and glass ceramic based on upconversion luminescence for optical thermometry

Optical thermometry has attracted growing consideration due to its outstanding performance. In this research, precursor glass with compositions of 50SiO₂–20Al₂O₃–30CaF₂–0.5ErF₃–1YbF₃ and the corresponding CaF₂ glass ceramic were prepared for optical temperature sensing comparison. A large enhancement in upconversion luminescence originated from thermally coupled energy levels (²H_11/2 and ⁴S_3/2) and ⁴F_9/2 was confirmed in the transparent glass ceramic (GC). Importantly, the temperature-dependent upconversion fluorescence intensity ratios of glass and GC were investigated from 303 K to 573 K under a 980 nm laser with constant pumping power. It was found that GC shows weaker optical thermometry ability than the precursor glass in terms of temperature sensitivity, the maximum relative sensitivity of GC reached to 10.6 × 10⁻³ K⁻¹ at 303 K while that of the glass is 11.15 × 10⁻³ K⁻¹ at 303 K, the thermally coupled energy gap reduced about 34.2 cm⁻¹ after crystallization, we attribute this change to the crystal field effect. Furthermore, the FIR value variation of glass shows weaker pumping power dependence than GC in terms of thermal effect induced by laser. The temperature-cycle measurements suggest that both glass and GC exhibit favorable thermal stability. Consequently, our results may contribute to enriching our understanding of the optical temperature sensing properties of glass and glass ceramic in other systems and provide a comprehensive perspective to design practical optical thermometry materials.

Optical thermometry comparison between glass and corresponding glass ceramic and understand difference for optimized temperature sensing materials.

UV and Temperature-Sensing Based on NaGdF4:Yb3+:Er3+@SiO2-Eu(tta)3

A multifunctional nanosystem was synthesized to be used as a dual sensor of UV light and temperature. NaGdF4:Yb3+:Er3+ upconverting nanoparticles (UCNPs) were synthesized and coated with a silica shell to which a europium(III) complex was incorporated. The synthesis of NaGdF4 UCNPs was performed via thermal decomposition of lanthanide ion fluoride precursors in the presence of oleic acid. To achieve sufficient water dispersibility, the surface of the hydrophobic oleate-capped UCNPs in the hexagonal phase was modified by a silica coating through a modified Stöber process through a reverse microemulsion method. An Eu(tta)3 (tta: thenoyltrifluoroacetonate) complex was prepared in situ at the silica shell. A dual-mode nanothermometer was obtained from a near infrared to visible upconversion fluorescence signal of Er3+ ions together with UV-excited downshifting emission from the Eu3+ complex. Measurements were recorded near the physiological temperature range (293-323 K), revealing excellent linearity (R 2 > 0.99) and relatively high thermal sensitivities (≥1.5%·K-1). The Eu(tta)3 complex present in the silica shell was tested as the UV sensor because of the Eu3+ luminescence dependence on UV-light exposure time.