Luminescence Intensity Ratio Research Articles

Temperature sensing performance of Er3+:Yb3+ co-doped CaF2 ceramic powders using near-infrared light

Luminescent materials for application in temperature sensing have caught a lot of interest in recent years. Particularly erbium (Er3+)-doped fluoride-based materials (EFM), which are readily accessible by near-infrared (NIR) excitation to produce efficient photon conversion. It has been established that ytterbium (Yb3+) may improve the performance of EFMs in both bulk and nanostructured forms by energy transfer channels among rare-earth ions in interstitial clusters. In this work, a comprehensive analysis of the Er3+:Yb3+:CaF2 crystalline structure, photoluminescence, and energy transfer from Yb3+ to Er3+ is presented for powders prepared by combustion synthesis. The Er3+:Yb3+:CaF2 powders display exceptional photon down-shift and up-conversion when exposed to NIR light (λ = 975 nm). The luminescence spectral change of the NIR emission around 1.5 μm, which corresponds to the Er3+ electronic transition 4I13/2 → 4I15/2, was investigated in a temperature range of 298–423 K for application in temperature sensing of biological systems exploring the third biological window. The luminescence intensity ratio technique was applied to the thermally coupled Stark sublevels of states 4I13/2 and 4I15/2 with the highest estimated temperature relative sensitivity being around 0.4 %/K at 298 K.

A novel ultrahigh-sensitive optical thermometer based on inverse thermal responses of Nd3+ and Yb3+ emissions in BaGd2(MoO4)4 phosphor

Nowadays, lots of efforts have been vested on the exploitation of novel luminescent thermometric materials to achieve remote temperature readout with ultra-high sensitivity and sub-degree resolution. Herein, the BaGd2(MoO4)4: Yb3+, Nd3+ phosphors were successfully prepared via a solid-state reaction method, and their concentration/temperature-dependent luminescence behaviors were investigated systematically. Upon 980 nm excitation, the photoluminescence (PL) spectra consisted of three emission bands centered at 754 nm, 805 nm and 872 nm from Nd3+, together with an emission band peaked at 1008 nm from Yb3+. As the temperature elevated, the Yb3+: 2F5/2 → 2F7/2 emission weakened sharply, whereas the promoted phonon-assisted energy transfer process from Yb3+ to Nd3+ and excited-state absorption process of Nd3+ led to an intense thermal enhancement of the Nd3+: 4Fj → 4I9/2 (j = 7/2, 5/2, 3/2) transitions. Moreover, the thermally enhancing factor was found to depend on the Nd3+ concentration. By utilizing the luminescence intensity ratio (LIR) technique, the temperature sensing behaviors based on thermally coupled levels (Nd3+: 4Fj, j = 7/2, 5/2, 3/2) and non-thermally coupled levels (Nd3+: 4Fj and Yb3+: 2F5/2) were studied at the different doping concentrations. When the temperature sensing was based on LIR between Nd3+: 4F3/2 → 2I9/2 and Yb3+: 2F5/2 → 2F7/2 transitions, the BaGd2(MoO4)4: 3 mol%Nd3+, 15 mol%Yb3+ sample displayed excellent thermal sensitivity (2.28–8.42 %K−1) and temperature resolution (0.1–0.22 K) at temperatures ranging from 298 K to 573 K, which were superior to those of many other reported luminescence materials. The present work might give a new input for developing near-infrared (NIR) luminescence materials with desirable temperature sensing performances.

Multi-strategy ratiometric luminescent thermometry based on Dy doped CaWO4 phosphors independent of excitation wavelength

This paper explores the detailed photoluminescence (PL) behaviors of Dy3+ doped CaWO4 (Dy:CaWO4) phosphors under multi-ultraviolet wavelength excitation. Moreover, it proposes multi-strategy ratiometric thermometry based on luminescence intensity ratio (LIR) from the transitions of thermally coupled energy levels (TCLs) of Dy3+. Under excitation of multiple ultraviolet wavelengths, the Dy:CaWO4 phosphors exhibited multi-wavelength responsive PL characteristics of Dy3+ with strong blue and yellow emissions from Dy3+ TCLs transitions. The temperature-dependent PL properties of Dy:CaWO4 phosphors were investigated over a temperature range of 300∼650 K. Multi-strategy ratiometric luminescent thermometry was examined under various excitation wavelengths by the thermal equilibrium population of Dy3+ TCLs. The proposed six LIR schemes based on the PL emissions of Dy3+ exhibited a good quantitative relationship with temperature. They showed well-luminescent thermometric behaviors with high absolute and relative sensitivities due to the largest energy gap of TCLs and a relatively larger LIR value. The thermometry properties of the multiple LIR schemes were independent of excitation wavelength, attributed to the stable site symmetry of Dy3+ and the thermal equilibrium population of TCLs under different excitation wavelengths. The multi-strategy ratiometric thermometry of Dy3+ demonstrated the merit of high sensitivity, excellent stability, and repeatability, indicating the potential luminescent thermometric application of Dy:CaWO4 phosphors.

Multimode temperature self-monitoring in photothermal nanoplatform based on Na3InF6: Nd3+, Yb3+, Ho3+ phosphor

An accurate deep-tissue thermometer with excellent photothermal conversion efficiency is desired for effective photo-thermal therapy (PTT), which will minimize collateral damages to normal cells from overheating or ineffective treatment from insufficient heat. Herein, a nano-thermometer with Nd3+/Yb3+/Ho3+ tri-doped Na3InF6 was designed by hydrothermal method to real-time monitor tissue temperature, and its luminescent performance and temperature sensing behavior based on the luminescence intensity ratio (LIR) technology in the visible and near infrared regions were analyzed under 808 nm excitation. The advantage of temperature probes located in the near infrared (NIR) biological window region was demonstrated by the penetration depth in simulating biological tissue agar. Furthermore, the feasibility of the sample as a self-monitoring photothermal platform was verified by in vitro bactericidal experiments, which expressed excellent photothermal conversion performance and sterilizing rates reached 59.8 % (E. coli) and 53.6 % (S. aureus), respectively. Results demonstrated that the present single-phased Na3InF6:Nd3+/Yb3+/Ho3+ nanophosphor could serve as a bifunctional photothermal agent with internal tissue temperature measurement and photothermal conversion.

Ultrasensitive NIR-II Ratiometric Nanothermometers for 3D In Vivo Thermal Imaging.

Luminescent nanothermometry, particularly the one based on ratiometric, has sparked intense research for non-invasive in vivo or intracellular temperature mapping, empowering their uses as diagnosis tools in biomedicine. However, ratiometric detection still suffers from biased sensing induced by wavelength-dependent tissue absorption and scattering, low thermal sensitivity (Sr ), and lack of imaging depth information. Herein, this work constructs an ultrasensitive NIR-II ratiometric nanothermometer with self-calibrating ability for 3D in vivo thermographic imaging, in which temperature-insensitive lanthanide nanocrystals and strongly temperature-quenched Ag2 S quantum dots are co-assembled to form a hybrid nanocomposite material. Precise control over the amount ratio between two sub-materials enables the manipulation of heat-activated back energy transfer from Ag2 S to Yb3+ in lanthanide nanoparticles, thereby rendering Sr up to 7.8% °C-1 at 43.5 °C, and higher than 6.5% °C-1 over the entire physiological temperature range. Moreover, the luminescence intensity ratio between two separated spectral regions within the narrow Yb3+ emission peak is used to determine the depth information of nanothermometers in living mice and correct the effect of tissue depth on 2D thermographic imaging, and therefore allows a proof-of-concept demonstration of accurate 3D in vivo thermographic imaging, constituting a solid step toward the development of advanced ratiometric nanothermometry for biological applications.

Naphthalimide-Tagged Iron(II) Spin Crossover Complex with Synergy of Ratiometric Fluorescence for Thermosensing.

Spin crossover (SCO) materials that possess switchable and cooperative fluorescence have long focused interest in photonic sensor devices to monitor the variations in the physicochemical parameters of the external environment. However, the lack of quantified cooperativity for the SCO transition operating in isolated molecules is detrimental to short-term technological applications. In this study, a pretwisted energy D-A system combining the deep-blue naphthalimide fluorophore (donor) and the FeN6 SCO chromophore (switchable acceptor) has been developed with the formula of Fe(naph-abpt)2(NCS)2·2DMF (1), where naph-abpt is N-[3,5-di(pyridin-2-yl)-4H-1,2,4-triazol-4-yl]-1,8-naphthalimide. Dual emission from the naphthalimide function based on its vibronic structure exhibits a different synergy effect with SCO, providing a new platform for ratiometric fluorescence thermosensing. Theoretical calculations and optical experimental results demonstrate an excellent correlation between luminescence intensity ratio signals and magnetic data of spin transition, promising a high sensitivity of the optical activity of the ligand to the spin state of the active iron(II) ions, with the maximum relative sensitivity as 0.7% K-1 around T1/2.

Near-infrared to visible up-conversion in Er3+ doped LaAlO3 phosphors and their assessment as an optical temperature sensor

The present work studies the optical temperature sensing in micro and nanospheres of LaAlO3, synthesized by a Pechini sol-gel method. The optical properties focus on the up-conversion emission and optical temperature sensing properties of thermally and non-thermally coupled levels. Exciting at 975 nm, the up-conversion produces three emissions bands centered at 533, 545, and 670 nm. When the concentration of Er ion increases, the intensity of emission increases up to 5 %. The mechanism shows the absorption of two photons and the energy transfer up-conversion process. Optical temperature sensing is studied in the range of 299–327 K based on thermal coupled and non-thermal coupled levels by the luminescence intensity ratio technique. The absolute sensitivity, relative sensitivity, and uncertainty temperature values were obtained to study the material's performance and applicability. The maximum absolute and relative sensitivity values are 5.21 × 10−3 K−1 at 327 K for I670/I545 and 0.87 % at 299 K for I533/545. On the other hand, the temperature uncertainty is 0.2 K, indicating that the present material may be used as an effective temperature-sensing device using thermal coupled and non-thermal coupled levels.

Th4+ Co‐doped YF3 : Yb3+, Er3+ Nanostructures for Enhanced Visible and NIR‐II Emissions and Potential Application as Cryogenic Thermometer

AbstractRemarkable enhancement in green and red upconversion (UC) emissions by 124 and 88 %, respectively was achieved whereas down‐conversion (DC) luminescence in NIR‐II region (~1540 nm) was improved by 20 % in Th4+ co‐doped YF3 : Yb3+,Er3+ nanocrystalline particles. The same is ascribed to lowering of symmetry via formation of asymmetric Er−F bonds and less symmetric Y3+ sites due to distortions on Th4+ co‐doping. Benefiting from the distinct temperature response of stark sublevels of the 4S3/2 and 4F9/2 states, we have proposed a strategy for luminescence intensity ratios (LIR) based thermometry involving thermally coupled (TCL) stark sub‐levels. This can be promising in more accurate temperature read‐out at cryogenic temperatures (~ −193 °C). Using the same, high Sa and Sr values of 0.0139 K−1 (80 K) and 0.682 % K−1(80 K) were obtained for 4S3/2 (1)/4S3/2 (2)→4I15/2 transitions. Higher Sa and Sr values of 0.226 K−1 (80 K) and 2.627 %K−1(80 K) were obtained for 4F9/2 (1)/4F9/2 (2)→4I15/2 transitions. The high sensitivity values were obtained than that reported for the YF3 host. We believe this work with improved UC luminescence on Th4+ addition will be boon to cryogenic temperature‐sensing.

Studies of luminescence traits and Judd-Ofelt analysis of Sm3+ activated oxyfluoride glasses

Novel Sm3+ activated oxyfluoride glass was synthesized via the melt-quenching approach with subsequent heat treatment. The X-ray diffraction measurement discloses the amorphous nature of prepared glasses. And, FTIR illustrates the molar surplus of Bi2O3 raises the network connectivity by creating bridging oxygen sites in the structure. The Judd-Ofelt (J-O) intensity parameters exhibit Ω4>Ω2>Ω6 trend, witnessing the rigidity of the glass structure and ionic bonding between Sm3+ ions and surrounding ligands. The 4G5/2 → 6H7/2 transition of Sm3+ is the most applicable for reddish-orange lasers due to their higher values of radiative transition probability, branching ratio, and stimulated emission cross-section. The optimum emission intensity is obtained with 30 mol% Bi2O3 and the corresponding decay time is 1.40 ms. Additionally, the F30 glass sample was lit in a reddish-orange region having a CCT value of 1689 K. The thermal luminescence quenching of the prepared glass was studied and the thermal stability parameters activation energy was estimated. Further, the contactless optical thermometry capability of the glass sample was explored within the range of 303 K–603 K using the luminescence intensity ratio (LIR) technique. Thus, the above studies on the glass sample suggest that it can be used as an active medium in lasers, contactless optical temperature sensing, and high-energy scintillator applications.

Optical Temperature Sensing Based on Linear Change of Luminescence Intensity Ratio in Y2O3: Tm3+, Eu3+ Phosphors.

In this work, Y2O3: Tm3+, Eu3+ phosphors were made by homogeneous precipitation with urea as precipitator. The emission spectra varying with temperature of Y2O3: Tm3+, Eu3+ phosphors were measured and analyzed. Analysis show that the luminescence of Eu3+ represents a normal thermal quenching change, while that of Tm3+ exhibits slow thermal enhancement phenomenon. In the temperature range of 303-503K, the luminescence of Tm3+ showed a trend of first strengthening and then weakening. The reason for this phenomenon of Tm3+ is that there is energy transfer from Eu3+ to Tm3+, and the energy transfer efficiency increases gradually with temperature. Meanwhile, the luminescence of Tm3+ also have thermal quenching effect. Under the combined influence of thermal quenching and energy transfer, the luminescence of Tm3+ first becomes stronger and then then becomes weaker. According to the calculation, the luminescence intensity ratio (LIR) of Tm3+ and Eu3+ conforms to the linear empirical formula with increasing temperature. The relative sensitivity of phosphors decreases with Eu3+ concentration increased, and the maximum Sr reaches 0.460% K-1 (1% Tm3+, 0.3% Eu3+, at 303K). Moreover, the temperature cycle test present that the LIR of phosphors has good repeatability.

Achieving thermochromic upconversion of Tm3+ for high-sensitive nanoprobe and information encryption

Upconversion-based optical thermometry has many merits, such as quick temperature response, higher thermal sensitivity and robust reliability. However, the previous works were mainly focused on the thermally coupled emissions, limiting their thermal sensitivity due to the intrinsic constraint by small energy gaps (e.g., <2000 cm−1) according to Boltzmann distribution theory. Here, we report a design of NaYF4:Yb3+/Tm3+@NaYF4 core-shell nanostructure to achieve thermochromic upconversion and high thermal sensitivity by taking advantage of nonthermally coupled upconversion emissions of Tm3+. We show that the blue upconversion emission of Tm3+ at 475 nm (1G4→3H6) exhibits a regular decrease with elevating temperature, while its deep-red emission at 696 nm (3F2,3→3H6) presents an increase. Such a feature leads to a rapid rise of luminescence intensity ratio (I696 nm/I475 nm) and the optimal relative sensitivity (Sr) reaches 2.79 % K−1 (503 K). More interestingly, the sample gives rise to a gradual emission color change from blue to purplish-red with lifting temperature. Our results offer a new class of upconversion-based nonoprobe with high thermal sensitivity and observable emission color variation, showing a great potential for nanoprobe and information security.

Nd3+ doped oxide thermal probes based on luminescence intensity ratio within BW-II and excitation in BW-I

The Nd3+ have taken a central place in the field of nanothermometry thanks to the presence of several narrow Stark emission and is easily excited through the lasers commercially available. With the goal to boost the development of Nd3+-based nanothermometers, especially working with emissions into BW-II, the thermal response of different oxide matrices Y2O3, Y2Ge2O7, Y3Al5O12, YBO3, and Y3BO6 were evaluated considering emissions from the Nd3+ 4F3/2 → 4I11/2 transition, which falls into the BW-II. Interestingly, we observed these lines are more intense than those located in BW-I, which can enhance the signal-to-noise ratio. Therefore, the design of thermal probes emitting in BW-II showed to be an excellent strategy to provide more accurate thermal sensing as the scattering of the light by the tissues is reduced in BW-II. In light of this, we also maximized the luminescence intensity of the matrices by Nd3+ doping from 0.1 to 10 mol%. Furthermore, their structure and luminescence properties were investigated using X-ray diffraction, transmission electron microscope, diffuse reflectance spectroscopy, photoluminescence, and radiative decay curve measurements. Additionally, exploring thermal response and luminescence emission optimization in several compounds offers enriched information support to design new high-level Nd3+-based thermal probes. Among Y2O3, Y2Ge2O7, Y3Al5O12 (YAG), YBO3, and Y3BO6 matrices studied, Y2O3 is the promising matrix to conduct thermal sensing due to exhibiting the highest Sr value around 0.4 %.K−1 in which 0.5 mol% Nd3+ is the deal doping to maximize its luminescence intensity.

Highly Sensitive Optical Manometer Based on the Visible Emissions of Ce3+‐Doped La6Sr4(SiO4)6F2 Multisite Phosphors

AbstractFor overcoming the unsatisfactory sensitivity of optical manometers and the susceptibility of manometric parameters to temperature changes, a series of Ce3+‐doped La6Sr4(SiO4)6F2 phosphors with multicolor emissions are developed. Excited by 375 nm, the resultant compounds exhibit asymmetric and broad emission bands, which can be easily deconvoluted into two peaks originating from seven to ninefold coordinated Ce3+ sites, where their intensities are dependent on the excitation wavelength. Through analyzing the pressure‐related luminescence intensity ratio (LIR) derived from these two Ce3+ sites, it is clear that the final manometer exhibits an unprecedentedly high relative sensitivity of ≈ 425% GPa−1 at 0.76 GPa (the highest value reported to date). As pressure increases, the emitting color tunes from yellow to blue, resulting in the possibility of visual pressure sensing. Furthermore, based on the color coordinates of the phosphor material, its pressure sensing capability is discussed, in which the maximum sensitivities are 24.38 and 27.74% GPa−1 at 0.76 GPa, when x‐coordinate and y‐coordinate are employed, respectively. Additionally, the LIR value is only slightly affected by temperature, leading to a thermal invariability manometric factor (TIMF) &gt; 400 K GPa−1. The findings indicate that Ce3+‐doped La6Sr4(SiO4)6F2 phosphors are good luminescent candidates for optical and visual multi‐mode manometers.

Upconversion luminescence and optical thermometry behaviors of Yb3+ and Ho3+ co-doped GYTO crystal

Optical thermometry based on the upconversion (UC) luminescence intensity ratio (LIR) has attracted considerable attention because of its feasibility for achievement of accurate non-contact temperature measurement. Compared with traditional UC phosphors, optical thermometry based on UC single crystals can achieve faster response and higher sensitivity due to the stability and high thermal conductivity of the single crystals. In this study, a high-quality 5 at% Yb3+ and 1 at% Ho3+ co-doped Gd0.74Y0.2TaO4 single crystal was grown by the Czochralski (Cz) method, and the structure of the as-grown crystal was characterized. Importantly, the UC luminescent properties and optical thermometry behaviors of this crystal were revealed. Under 980 nm wavelength excitation, green and red UC luminescence lines at 550 and 650 nm and corresponding to the 5F4/5S2 → 5I8 and 5F5 → 5I8 transitions of Ho3+, respectively, were observed. The green and red UC emissions involved a two-photon mechanism, as evidenced by the analysis of power-dependent UC emission spectra. The temperature-dependent UC emission spectra were measured in the temperature range of 330–660 K to assess the optical temperature sensing behavior. At 660 K, the maximum relative sensing sensitivity (Sr) was determined to be 0.0037 K−1. These results highlight the significant potential of Yb,Ho:GYTO single crystal for optical temperature sensors.Graphical abstract

Rectangular cross-sectional Nd3+/Yb3+ co-doped AlN nanorods with strong up-conversion emission for high-sensitivity optical thermometry

Due to the characteristics of non-contact, high sensitivity and spatial resolution, nanoscale optical thermometry is necessary in many applications such as micro/nano electronics, integrated optics and biomedicine. Herein, we report the synthesis of Nd3+/Yb3+ co-doped AlN (AlN:Nd3+/Yb3+) nanorods using an arc discharge method and investigate their phase, composition and morphology using XRD, Raman, XPS, EDS, ICP, SEM and TEM. The nanorods with rectangular cross-section are highly single crystalline and have a uniform smooth surface. Upon excitation at 980 nm, AlN:Nd3+/Yb3+ nanorods exhibit up-conversion (UC) visible emission bands (around 544, 595 and 667 nm) and near-infrared emission bands (around 755 and 806 nm), which correspond to intra-4f electron transitions of the Nd3+ ions. Later, the temperature dependence of UC luminescence behavior was systemically studied using luminescence intensity ratio (LIR) technique. It was verified that LIRs with non-thermally coupled levels (4G7/2/4F5/2 or 4G7/2/4F7/2) are suitable for temperature sensing. The maximum relative sensitivity based on 4G7/2/4F7/2 is 4.63% K−1 at 298 K, which is one of the highest values reported for optical thermometers. This work provides an efficient method for synthesizing wide-band gap semiconductors with doped size-mismatched functional atoms that can be used for high-sensitivity optical thermometry.

Bimetallic Eu/Tb Complexes for Ratiometric Temperature Sensing with Unusual Enhancement of Eu Luminescence with Temperature

In this paper we describe the results of the influence of temperature in the range of 280–340 K on the luminescence of bimetallic Eu/Tb complexes with N-heterocyclic ligand L based on 2,2′-bipyridyldicarboxylic acid in acetonitrile. The experiments were carried out for systems with various Eu/Tb ratios. The stability of the complexes of the ligand L with metal M (Eu or Tb) was determined using spectrophotometric titration in acetonitrile solutions. The LM complexes’ stability constants were found to be typical for these systems; however, the stability of Eu complex is slightly higher than that for Tb. Along with rising temperature, we observed a decrease in Tb emission intensity and, at the same time, an enhancement in Eu luminescence. An explanation of Eu luminescence enhancement involves the appearance of charge transfer states, bands of which can be observed in the Eu luminescence excitation spectra as difference spectra measured with two close temperatures. The unusual Eu luminescence enhancement upon heating was observed for the first time for the complex with tetradentate O,N-type heterocyclic diamide ligand L, while an inverse phenomenon was observed with the Tb luminescence. The Eu luminescence enhancement was found earlier for various carboxylate complex salts, but not for heterocyclic coordination complexes. This allows the construction of a ratiometric luminescent thermometer in the range of 280–340 K using the ratio of luminescence intensities for Eu and Tb. The stability constants for the individual Eu and Tb complexes help us to understand the equilibrium in L:Tb:Eu complex system and shed light on plausible speciation in solution.

Realization of plant growth lighting and temperature detecting based on novel Bi3+, Sm3+ and Mn4+ doped Ca2GdNbO6 double perovskite phosphors

The Bi3+ or Sm3+ ions are introduced into Mn4+-activated Ca2GdNbO6 (CGN) double perovskite phosphors to achieve highly efficient plant growth lighting and temperature measurement. Here, the energy band and density of states for CGN are computed using density functional theory (DFT) in detail. The emission bands of CGN: Bi3+/Mn4+ consist of both the blue-light band (3P1→1S0 transition of Bi3+ ions) and red-light band (2E→4A2 transition of Mn4+ ions), which solves the issue of the lack of blue light in Mn4+-activated phosphors used in plant-growth LEDs. The electroluminescence emission spectrum of the LEDs assembled with CGN: Sm3+/Mn4+ shows a wide emission band (550–800 nm), which coincides perfectly with the absorption (550–825 nm) of Phytochrome (PR and PFR). Moreover, non-contact thermometers are designed by luminescence intensity ratio technique (LIRMn/Bi or LIRMn/Sm) with excellent absolute (Sa = 0.074 K-1@448 K or 0.036 K-1@373 K) and relative sensitivity (Sr = 2.13 %K−1@498 K or 1.11 %K−1@448 K). The results reveal that as-prepared phosphors have great potential in promoting indoor plant cultivate and optical temperature sensing.

Luminescent thermometry with YVO4:Er/Nd: Achieving high sensitivities within the 1st and 2nd biological windows

YVO4:Er3+, Nd3+ powders were prepared by the modified sol gel synthesis route using glucose as chelating agent and characterized by X-ray powder diffraction (XRD) and scanning electron microscope (SEM). Under 660 nm excitation, four infrared emission bands located between 790 and 845 nm, 870 and 930 nm, 950 and 1030 nm, and between 1050 and 1100 nm were observed, and were assigned the transitions 4F5/2 – 4I9/2 (Nd) and 4I9/2 – 4I15/2 (Er), 4F3/2 – 4I9/2 (Nd), 4I11/2 – 4I15/2 (Er), and 4F3/2 – 4I11/2 (Nd), respectively. The performance of these powders as optical temperature sensors using the luminescence intensity ratio (LIR) technique between thermally coupled levels (TCLs) and non-thermally coupled levels (non-TCLs) was studied within the temperature range of 293–373 K. Using different combinations of the emission intensities at 809, 880, 914 and 1003 nm, three distinct (LIR) temperature sensors schemes were built, with both excitation and emission within the first and second biological window. These LIRs relative sensitivity (Sr) and temperature uncertainties (δT) were investigated for samples with different Er and Nd concentrations. Sr values up to 2.08 ± 0.03%. K−1 and δT smaller than 1 K, were obtained. Repeatability and reproducibility tests demonstrated the reliability of the proposed LIRs.

Ratiometric optical temperature sensor with wide range and high sensitivity based on the emission of Dy3+ ion-doped Ca5(PO4)2SiO4 phosphor

There is an urgent demand for the development of non-contact optical temperature sensors that possess a wide temperature measurement range and high sensitivity, particularly for extreme environments. In this study, Dy3+-doped Ca5(PO4)2SiO4 phosphors were prepared and comprehensively analyzed. XRD, SEM, EDS, Raman spectrum, as well as excitation and emission spectrum were employed to investigate the structural, photoluminescent, and temperature-dependent properties of the phosphors. Under 349 nm excitation, the luminescence intensity ratio (LIR) of Dy3+ ions at 453 nm (4I15/2) and 480 nm (4F9/2) exhibited a strong correlation with temperature within the range of 296-1073 K. By fitting the FIR of I453 and I480 at different temperatures using Boltzmann equations, we observed a larger energy gap, indicating high relative sensitivity of the synthesized phosphor. Additionally, Ca4.95(PO4)2SiO4: 0.05Dy3+ phosphor shows excellent temperature repetitiveness. These findings highlight the potential applications of Ca5(PO4)2SiO4: Dy3+ phosphors as highly sensitive ratiometric optical temperature sensor over a wide temperature range.

Thermally boosted upconversion luminescence and high-performance thermometry in ScF3:Yb3+/Tm3+ nanorods with negative thermal expansion

Luminescence nanothermometers featuring high spatial resolution and thermal resolution have aroused extensive interest in biological and nanomedical fields. However, the challenge of thermal quenching in upconversion (UC) nanocrystals hampers achieving elevated relative temperature sensitivity (Sr). In this study, the quasi cubic nanorods of ScF3:Yb3+/Tm3+ with negative thermal expansion were prepared, and thermally boosted luminescence was found to derive from the phonon-assisted energy transfer, resulting in the emission band of 3F2,3 → 3H6 of Tm3+ ions enhanced monotonously. While the emission bands of (1G4)1D2→3F4 of Tm3+ ions first increased slightly and then decreased seriously because of the competition between phonon-assisted and cross-relaxation (CR) processes. Relying on this high-contrast thermal dependent feature, the maximum relative sensitivity of 1.60% K−1 at 523 K was achieved in the proposed luminescence intensity ratio (LIR) thermometry. These findings would open a new avenue for designing thermally boosted upconversion nanocrystals and reliable optical thermometers by using Tm3+ activated luminescent materials.