Ratiometric Temperature Research Articles

Single Excited Dual Band Luminescent Hybrid Carbon Dots-Terbium Chelate Nanothermometer.

The report introduces hybrid polyelectrolyte-stabilized colloids combining blue and green-emitting building blocks, which are citrate carbon dots (CDs) and [TbL]+ chelate complexes with 1,3-diketonate derivatives of calix[4]arene. The joint incorporation of green and blue-emitting blocks into the polysodium polystyrenesulfonate (PSS) aggregates is carried out through the solvent-exchange synthetic technique. The coordinative binding between Tb3+ centers and CD surface groups in initial DMF solutions both facilitates joint incorporation of [TbL]+ complexes and the CDs into the PSS-based nanobeads and affects fluorescence properties of [TbL]+ complexes and CDs, as well as their ability for temperature sensing. The variation of the synthetic conditions is represented herein as a tool for tuning the fluorescent response of the blue and green-emitting blocks upon heating and cooling. The revealed regularities enable developing either dual-band luminescent colloids for monitoring temperature changes within 25–50 °C through double color emission or transforming the colloids into ratiometric temperature sensors via simple concentration variation of [TbL]+ and CDs in the initial DMF solution. Novel hybrid carbon dots-terbium chelate PSS-based nanoplatform opens an avenue for a new generation of sensitive and customizable single excited dual-band nanothermometers.

Ultrasensitive Temperature Sensing Based on Ligand-Free Alloyed CsPbClx Br3-x Perovskite Nanocrystals Confined in Hollow Mesoporous Silica with High Density of Halide Vacancies.

Temperature sensing based on fluorescent semiconductor nanocrystals has recently received immense attention. Enhancing the trap-facilitated thermal quenching of the fluorescence should be an effective approach to achieve high sensitivity for temperature sensing. Compared with conventional semiconductor nanocrystals, the defect-tolerant feature of lead halide perovskite nanocrystals (LHP NCs) endows them with high density of defects. Here, hollow mesoporous silica (h-SiO2 ) template-assisted ligand-free synthesis and halogen manipulation (chloride-importing) are proposed to fabricate highly defective yet fluorescent CsPbCl1.2 Br1.8 NCs confined in h-SiO2 (CsPbCl1.2 Br1.8 NCs@h-SiO2 ) for ultrasensitive temperature sensing. The trap barrier heights, exciton-phonon scattering, and trap state filling process in the CsPbCl1.2 Br1.8 NCs@h-SiO2 and CsPbBr3 NCs@h-SiO2 are studied to illustrate the higher temperature sensitivity of CsPbCl1.2 Br1.8 NCs@h-SiO2 at physiological temperature range. By integrating the thermal-sensitive CsPbCl1.2 Br1.8 NCs@h-SiO2 and thermal-insensitive K2 SiF6 :Mn4+ phosphor into the flexible ethylene-vinyl acetate polymer matrix, ratiometric temperature sensing from 30.0 °C to 45.0 °C is demonstrated with a relative temperature sensitivity up to 13.44% °C-1 at 37.0 °C. The composite film shows high potential as a thermometer for monitoring the body temperature. This work demonstrates the unparalleled temperature sensing performance of LHP NCs and provides new inspiration on switching the defects into advantages in sensing applications.

Deciphering crystal structure and photophysical response of Bi3+ and Pr3+ co-doped Li3Gd3Te2O12 for lighting and ratiometric temperature sensing

Crystal structure and photophysical response of Bi3+ and Pr3+ co-doped Li3Gd3Te2O12 system was investigated for lighting and ratiometric temperature sensing applications. The double substitution at the dodecahedral site was confirmed via Rietveld refinement and Raman spectra analysis. Considering the full advantage of distinct and characteristic cyan and orange emissions of Bi3+ and Pr3+, the emission tunability towards white region was achieved by the proposed co-doping combination. The as-prepared Li3Gd3Te2O12: Bi3+, Pr3+ phosphor exhibited characteristic and enhanced emission of Pr3+ under the excitation of 297 nm. The activation energy of 0.29 eV was obtained for the co-doped matrix, exhibiting better thermal stability. Further, the temperature sensing properties were evaluated based on the temperature dependent photoluminescence emission and decay curves in the range 100–300 K. Notably, the as-prepared Li3Gd3Te2O12: Bi3+, Pr3+ phosphor showed a maximum relative sensitivity of 0.672% K−1, as based on decay curve method, indicating that the phosphor can act as a potential candidate for optical temperature sensing in the physiological range. These findings demonstrate the efficiency of new co-doping combination Bi3+-Pr3+ for designing multifunctional phosphors.

Vibrationally Induced Photophysical Response of Sr2NaMg2V3O12:Eu3+ for Dual‐Mode Temperature Sensing and Safety Signs

In the dual‐emitting Eu3+‐activated Sr2NaMg2V3O12 garnet, vibrationally induced thermometric response and thermochromic luminescence are investigated for the first time. Based on the diverse thermal quenching of VO43− and Eu3+ along with the advantage of variation in the fluorescence intensity ratio, a potential phosphor for sensitive dual‐mode ratiometric and colorimetric temperature sensors is proposed in which maximum absolute and relative sensitivity of 0.0135 K−1 and 1.61% K−1 are obtained at 420 K with a temperature resolution <0.2 K. Efficient thermochromic luminescence in which colorific shift from white (300 K) to red (500 K) is observed such that the requirement of larger number of phonons weakens the nonradiative relaxation of Eu3+, resulting in slow quenching, substantiated by estimating radiative and nonradiative decay rates by the 4f–4f intensity method. In contrast, a strong vibrational coupling of excited electrons of the VO43− complex is identified and verified by means of temperature‐dependent Raman and photoluminescence excitation spectra for the first time. Consequently, an increased thermal population of vibrational levels favors rapid thermal quenching of luminescence of VO43− via crossover mechanism. Hence dual‐centered Sr2NaMg2V3O12:Eu is an efficient thermometric and thermochromic luminescent material for optical thermometry and safety sign applications in a high‐temperature environment.

Sensitive temperature reading from intensity ratio of Cr3+ and defects’ emissions in MgTiO3:Cr3+

The luminescence thermometry based on the intensity ratio of Cr3+ and host emissions in the Cr3+ activated MgTiO3 phosphor powder is demonstrated over the 100–350 K temperature range. Phosphor was prepared by a two-step procedure based on the sol-gel and molten salt methods. Rhombohedral crystal structure of the material is confirmed by X-ray diffraction analysis, and the mean crystallite size of the powder was calculated to be ~ 32 nm. Morphology was investigated using scanning electron microscopy showing ellipsoidal, densely packed grains with 100 nm–150 nm average size. Photoluminescence emission spectra recorded under 385 nm excitation showed the broad host emission centered at ~ 485 nm and the Cr3+ emission around ~ 700 nm. The temperature-dependent emission spectra showed that host-emission intensity is almost temperature invariant, while the intensity of the Cr3+ emission rapidly decreases from 200 K to 350 K. Such behavior theoretically modelled and further applied for the ratiometric luminescence temperature sensing showed the maximal relative sensitivity of ~ 2.6% K-1, temperature resolution of 0.3 K, and excellent repeatability.

Post-modification preparation of dual-emission Eu3+@ZnII MOFs-based hybrid material and its application in highly sensitive ratiometric sensing for asthma wonder drug-procaterol enhanced by HCO3- and temperature

Currently, procaterol has been widely used as an asthma wonder drug; however, the overuse of procaterol easily leads to arrhythmia, and tachycardia decreased blood pressure. Metal organic frameworks (MOFs) are a new class of hybrid porous materials that have attracted great attention in the past 20 years. These metal-organic framework composites have highly efficient host-guest interactions and are excellent fluorescent sensing materials. In this work, an effective detection method to control the amount of procaterol was designed. A unique three-dimensional (3D) cluster-based metal-organic framework (MOF), namely [Zn2L(DEF)3]n (Zn-MOF, H4L=[1,1′:4′,1′'-terphenyl]- 3,3′',5,5′'-tetracarboxylic acid) can be prepared through the solvothermal method. Furthermore, through postsynthesis strategies, Eu3+ is loaded into cluster-based Zn-MOF to form dual-emission Eu3+@Zn-MOF, which can be employed as a ratiometric photoluminescent sensor for detecting the amount of wonder drug procaterol with a high K sensing constant value (6.12 ☓ 105 [M−1]) and a low limit of detection (LOD) value (46.10 nM). In addition, HCO3- can be effectively detected with a low LOD value (8.28 nM) in procaterol solution while other anions do not respond, which also reveals the pharmacological effects between HCO3- and procaterol. Furthermore, in the HCO3- solution, Eu3+@Zn-MOF exhibits a more sensitive sensing performance for the procaterol with high sensitivity and excellent recovery. On the other hand, Eu3+@Zn-MOF is a highly sensitive ratiometric temperature sensor in the range of 298−353 K. The detection sensitivity of Eu3+@Zn-MOF towards procaterol under the different physicochemical temperatures of the human body (303 K, 308 K, and 313 K) is also compared, This comparision indicates that temperature of 303 K has an enhanced sensing performance for procaterol in comparison with other detection temperatures. In conclusion, with the help of HCO3- and a suitable temperature (303 K), the detection sensitivity of Eu3+@Zn-MOF towards procaterol can be significantly improved and enhanced.

Fluorescent polymeric nanoparticle for ratiometric temperature sensing allows real-time monitoring in influenza virus-infected cells

Temperature is a key indicator of infection and disease, however, it is difficult to measure at a cellular level. Nanoparticles are applied to measure the cellular temperature, and enhancement of the stability and reliability of the signal and higher biocompatibility are demanded. We have developed fluorescent polymeric nanoparticles loaded with temperature-sensitive units (as rhodamine B) and internal reference units (as coumarin) for imaging and ratiometric sensing of the cellular temperature in the physiological range. The fluorescence signal of the nanoparticles was stable in the bio-environment and the ratiometric sensing strategy could overcome the concentration effect of nanoparticles. The nanoparticles were endocytosed by cells and partially presented in mitochondria. The fluorescence intensity ratio of rhodamine B and coumarin using nanoparticles showed good linear correlations in buffer solutions, cell suspensions, and imaging of living cells. Using the fluorescent polymeric nanoparticles, the change of temperature of cells during influenza virus infection could be individually monitored.

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.

Dual-emitting phosphor Sr4Al14O25:Eu2+/3+ prepared in air for ratiometric temperature sensing

The Sr4Al14O25:Eu2+/3+ phosphor was synthesized in air via conventional high-temperature solid-state reaction. Eu3+ in the host lattice was partially self-reduced to Eu2+, and the characteristic excitation and emission of Eu2+ and Eu3+ were detected simultaneously. Due to the different temperature quenching mechanisms of Eu2+ and Eu3+, the luminescent performance and fluorescence intensity ratio of Eu2+/3+ co-activated phosphor presented great temperature dependence. With the increase of the operating temperature, the emitting color of the phosphor can be tuned from bluish green to white. The maximum absolute and relative temperature sensitivity of Sr4Al14O25:Eu2+/3+ phosphor can be as high as 0.015 K−1 at 525 K and 1.1% K−1 at 375 K, respectively. In addition, the decoupled emission peaks of Eu2+ and Eu3+ provide strong signal discrimination for temperature measurement. All the results indicate that the Sr4Al14O25:Eu2+/3+ phosphor possesses excellent temperature-sensing characteristic and can be a promising candidate for ratiometric optical thermometry applications.

Ratiometric temperature sensing behavior of dual-emitting Ce3+/Tb3+ co-doped Na5Y9F32 single crystal with high relative sensitivity

The Na5Y9F32 single crystals doped with fixed 0.5 mol% Ce3+ and various concentrations of Tb3+ (0, 0.4, 0.6 and 0.8 mol%) were grown by Bridgeman method. The luminescent properties, energy transfer (ET) and the ratiometric temperature sensing behavior were studied thoroughly. Under 315 nm excitation, the Ce3+/Tb3+ co-doped Na5Y9F32 single crystal mainly presented two emissions at blue 385 nm (Ce3+:5d→4 f) and green 545 nm (Tb3+:5D4→7F5). The color area can undergo from the purple-blue region (0.1643, 0.0768) to the green region (0.2585, 0.3604) by altering the content of Tb3+ ion from 0 to 0.8 mol%. The energy transfer between the Ce3+ and Tb3+ ions was confirmed by decay curves with emission spectra, and the maximum energy transfer efficiency (ETE) were estimated to be 45.1%. The mechanism of dipole-dipole interaction (d-d) for energy transfer from Ce3+ to Tb3+ can be explained by the formula of Dexter’s energy transfer. The fluorescence intensity ratio (FIR) of blue and green emission showed a linear relationship with temperature varying from 298 K to 473 K in the 0.5 mol% Ce3+/0.8 mol% Tb3+ co-doped Na5Y9F32 single crystal. Meanwhile, the 0.5 mol% Ce3+/0.8 mol% Tb3+ co-doped Na5Y9F32 single crystal possessed higher absolute sensitivity (Sa) of 0.0157 K−1, relative sensitivity (Sr) of 1.18% K−1 and temperature resolution (δT) of 0.086 K. By using the integrating spheres, the quantum yield (QY) of 0.5 mol% Ce3+/0.8 mol% Tb3+ co-doped Na5Y9F32 single crystal was measured as ~16.88%. These excellent optical properties suggest that the Ce3+/Tb3+ co-doped Na5Y9F32 single crystal with stable physical-chemical properties could have a far-reaching application prospect for the ratiometric optical thermometry.

3D printed optofluidic biosensor: NaYF4: Yb3+, Er3+ upconversion nano-emitters for temperature sensing

The nonintrusive, realtime, and accurate measurement of the local temperature has applications in a variety of scenarios. This need has led to significant research to develop novel nanophotonic sensors. In this paper, a 3D-printed optofluidic chip is nano-engineered for local, contactless, and precise optical measurement of temperature in microfluidic channels using lanthanide-doped upconversion nanoparticles. Temperature sensing nano-emitters are doped in a UV-curable matrix and embedded into a microfluidic channel using maskless photolithography. Photoluminescence of NaYF4:Yb3+, Er3+ upconversion nanoparticles have two bands in the green spectrum in which the PL maximums at 521 nm and 541 nm are used for temperature sensing. Thus, enabling ratiometric temperature sensing when excited using near-infrared light, which is desirable for measurements in biological and biomedical settings. The functionality of the temperature sensor for local and nonintrusive measurements in a microalgae culture medium is demonstrated.

Binuclear charged copper(I) complex as a multimode luminescence thermal sensor

Luminescence thermometry became one of the most rapidly developing scientific areas in the last decade. A lot of scientific groups are working on the design of a highly sensitive and accurate thermometer based on monitoring the chosen luminescence parameter. However, it is still a challenge to create a multimode sensor utilizing several temperature-dependent parameters for thermometry, which could broaden the working range and improve thermometric characteristics. Here, we successfully demonstrate the binuclear helical charged complex [L3Cu2](BF4)2 (L = 1-pyridine-2-ylphospholane) in head-to-head configuration with solid-state single-band emission as a multimode optical thermometer. Thermal sensing was provided using luminescence intensity ratio, spectral line position, bandwidth, and lifetime. Ratiometric temperature determination was performed by the successful use of deconvolution analysis. The thermometric performance was studied in terms of relative thermal sensitivity, which was varied from 0.93 % K−1 for line position to 0.11 % K−1 for bandwidth at 298 K. The obtained results show Cu(I) complex as a cheap multimode luminescence thermal sensor in the 98–393 K range.

Construction and Multifunctional Applications of Visible-Light-Excited Multicolor Long Afterglow Carbon Dots/Boron Oxide Composites

Compared to ultraviolet light, visible light as an excitation light source has lower phototoxicity and deeper penetrability. This is of importance to explore the application of long afterglow materials with visible light as the excitation wavelength. In this work, multicolor long afterglow materials excited by visible light were prepared by embedding carbon dots (CDs) in boron oxide (B₂O₃) and the formation of carbon–boron bonds, and the glassy state of B₂O₃ during the heating process protected the triplet excitons from being quenched, thereby promoting the emission of long afterglow. In addition, some CDs/B₂O₃ composites show dual-mode afterglow emission with thermally activated delayed fluorescence (TADF) and room-temperature phosphorescence (RTP) at the same time. These as-designed multicolor CDs/B₂O₃ composites exhibit a long lifetime of 445.9 ms, a high afterglow quantum efficiency of 17.61%, and high stability. Meanwhile, the afterglow can be observed at room temperature by the naked eye and lasts for several seconds when the visible light is just switched off. These as-obtained CDs/B₂O₃ composites with visible-light-excited multicolor long afterglow emission have shown potential in reversible ratiometric temperature sensing, latent fingerprint identification, information anticounterfeiting, and encryption.

Overview of N-Rich Antennae Investigated in Lanthanide-Based Temperature Sensing.

The market share of noncontact temperature sensors is expending due to fast technological and medical evolutions. In the wide variety of noncontact sensors, lanthanide-based temperature sensors stand out. They benefit from high photostability, relatively long decay times and high quantum yields. To circumvent their low molar light absorption, the incorporation of a light-harvesting antenna is required. This Review provides an overview of the nitrogen-rich antennae in lanthanide-based temperature sensors, emitting in the visible light spectrum, and discusses their temperature sensor ability. The N-rich ligands are incorporated in many different platforms. The investigation of different antennae is required to develop temperature sensors with diverse optical properties and to create a diverse offer for the multiple application fields. Molecular probes, consisting of small molecules, are first discussed. Furthermore, the thermometer properties of ratiometric temperature sensors, based on di- and polynuclear complexes, metal-organic frameworks, periodic mesoporous organosilicas and porous organic polymers, are summarized. The antenna mainly determines the application potential of the ratiometric thermometer. It can be observed that molecular probes are operational in the broad physiological range, metal-organic frameworks are generally very useful in the cryogenic region, periodic mesoporous organosilica show temperature dependency in the physiological range, and porous organic polymers are operative in the cryogenic-to-medium temperature range.

The impact of 2H9/2 → 4I13/2 emission from Er3+ ions on ratiometric optical temperature sensing with Yb3+/Er3+ co-doped upconversion materials

Yb3+/Er3+ co-doped upconversion materials are widely used for luminescence intensity ratio (LIR) thermometry, where the relative intensity ratio of the green luminescence transitions (2H11/2 → 4I15/2 and 4S3/2 → 4I15/2) of Er3+ dopant ions changes with temperature. In this work we report on the impact of an additional transition from the 2H9/2 level to the intermediate 4I13/2 level, which overlaps with the green luminescence normally used for LIR thermometry. The 2H9/2 → 4I13/2 emission overlaps extensively with the 4S3/2 → 4I15/2 emission and is more sensitive to pump power. The wavelength intervals used to integrate both 2H11/2 → 4I15/2 and 4S3/2 → 4I15/2 luminescence need be selected carefully in order to achieve accurate temperature readouts.

Embedding Red Emitters in the NbO-Type Metal-Organic Frameworks for Highly Sensitive Luminescence Thermometry over Tunable Temperature Range.

The intrinsic advantages of metal-organic frameworks (MOFs), including extraordinarily high porosities, tailorable architectures, and diverse functional sites, make the MOFs platforms for multifunctional materials. In this study, we synthesized two kinds of isostructural NbO-type Zn2+-based MOFs, where two structurally similar tetracarboxylate ligands, 5,5'-(pyrazine-2,5-diyl)diisophthalic acid (H4PZDDI) and 5,5'-(pyridine-2,5-diyl)diisophthalic acid (H4PDDI), with pyridine or pyrazine moieties, were employed as the organic linkers. By embedding the red-emitting cationic units of pyridinium hemicyanine dye 4-[p-(dimethylamino)styryl]-1-methylpyridinium (DSM) and trivalent europium ion (Eu3+), two types of composites, DSM@ZnPZDDI and DSM@ZJU-56 and Eu3+@ZnPZDDI and Eu3+@ZJU-56, were harvested and evaluated for use as potential ratiometric temperature probes. The temperature-responsive luminescence of these dual-emitting composites was investigated, and their representative features of relative sensitivity, temperature resolution, spectral repeatability, and luminescence color change were discussed. Importantly, compared with the DSM-incorporated composites, Eu3+@ZnPZDDI and Eu3+@ZJU-56 show a much wider sensing temperature range and higher relative sensitivities, suggesting the performance of the composites can be engineered by elaborately combining the host and guest units. Given the rich choices of porous MOFs and emitting units, such a strategy can be useful in the design and preparation of multifunctional dual-emitting sensory materials.

Characterizations and photoluminescence properties of a dual-functional La2LiNbO6:Bi3+, Eu3+ phosphor for WLEDs and ratiometric temperature sensing

In recent years, color-tunable luminescent materials based on multi-emitting centers have attracted considerable attention owing to their potential applications in display, lighting and temperature sensor. In this research, we have designed a novel single-phased La2LiNbO6:Bi3+, Eu3+ phosphor with dual-emitting centers and investigated its band structure, luminescence property and temperature sensitive behaviors. The structural and morphological analysis confirmed that the as-synthesized phosphor crystallized in a monoclinic double-perovskite structure with well dispersed elemental composition and good crystallinity. Under NUV excitation, Bi3+ single-doped La2LiNbO6 phosphor exhibited a broad blue emission band in the range of 350–650 nm, which was assigned to the characteristic 3P1 →1S0 transition of Bi3+ ion. On the other hand, efficient energy transfer from Bi3+ to Eu3+ ions was observed in Bi3+/Eu3+ co-doped La2LiNbO6 phosphors, leading to the tunable emission color changing from blue to red with increasing Eu3+ concentration. Furthermore, from the emission spectra and critical distance, the energy transfer between Bi3+ and Eu3+ ions was deduced to be a dipole-dipole interaction mechanism. Based on the temperature-dependent PL spectra, the thermal stability and temperature sensing properties of the La2LiNbO6:Bi3+, Eu3+ phosphor were discussed and the main parameters related to the temperature sensing performance were calculated. Finally, we have preliminarily evaluated the performance of La2LiNbO6:Bi3+, Eu3+ phosphor in WLED through analyzing the photoelectric parameters of the fabricated LEDs.

A novel green‐emitting SrLaAlO4:Er3+ phosphor synthesized by co‐precipitation method for w-LEDs and optical thermometry

A novel green-emitting Er3+ doped SrLaAlO4 phosphor has been synthesized successfully through one-step calcination of the precursor prepared by co-precipitation method. Meanwhile, the electronic structure and photoluminescence (PL) properties of the samples are investigated in detail. It is found that the strongest excitation peak among the several narrow excitation bands from 250 nm to 500 nm locates in near-UV region, indicating that the phosphor can match well with not only blue LED chips but also near-UV LED chips. Under the excitation of 377 nm light, the SrLaAlO4 phosphor can emit bright green light peaking at 527 nm and 548 nm simultaneously. In addition, the different responses of the two emission positions to temperature variation of SrLaAlO4:Er3+ phosphor have been verified and expounded. The temperature sensing properties of SrLaAlO4:Er3+ in a wide range of 298–573 K show a good exponential function relationship between ratiometric intensity and temperature (R2 > 0.999) as well as a high sensitivity (1.42% K− 1). Besides, the CIE coordinates diagram shows that this phosphor has an outstanding color stability. In view of the outstanding performance in the PL, thermal stability and sensitivity, SrLaAlO4:Er3+ phosphor can be promisingly applied in near ultraviolet converted white light LED devices (wLEDs) and optical thermometry.

Multi-stimuli programmable FRET based RGB absorbing antennae towards ratiometric temperature, pH and multiple metal ion sensing.

A red-green-blue (RGB) multichromophoric antenna 1 consisting of energy donors naphthalimides and perylenediimides and a central aza-BODIPY energy acceptor along with two subchromophoric red-blue (RB 6) and green-blue (GB 12) antennae was designed that showed efficient cascade Förster resonance energy transfer (FRET). RGB antenna 1 showed pronounced temperature-dependent emission behaviour where emission intensities in green and red channels could be tuned in opposite directions by temperature giving rise to unique ratiometric sensing with a temperature sensitivity of 0.4% °C. RGB antenna 1 showed reversible absorption modulation selectively in the blue region (RGB ↔ RG) upon acid/base addition giving rise to pH sensing behaviour. Furthermore, RGB antenna 1 was utilized to selectively sense metal ions such as Co2+ and Fe3+ through a FRET turn-off mechanism induced by a redox process at the aza-BODIPY site that resulted in the selective spectral modulation of the red band (i.e., RGB → GB). Model antenna RB 6 showed white light emission with chromaticity coordinates (0.32, 0.33) on acid addition. Antennae 1, 6 and 12 also exhibited solution state electrochromic switching characterized by distinct colour changes upon changing the potential. Finally, antennae 1, 6 and 12 served as reversible fluorescent inks in PMMA/antenna blends whereby the emission colours could be switched or tuned using different stimuli such as acid vapour, temperature and metal ions.

Regulation of double luminescence centers based on the evolution of disordered local structure for ratiometric temperature sensing applications

A “single site but two local environments” phenomenon in Sr2.99−xEu0.01La1+xP3−xSixO12 phosphors yields an applicable Sr of ≥1% K−1 in 303–530 K and a repeatability capability of over 99% for ratiometric temperature sensing applications.