Optical Pressure Sensor Based on the Emission and Excitation Band Width (fwhm) and Luminescence Shift of Ce3+-Doped Fluorapatite-High-Pressure Sensing

Enhanced Quantum Efficiency via Co-Substitution in Red-Emitting Phosphor Sr2[MgAl5N7] : Eu2+ for Advanced Spectroscopic Applications Including Laser Displays with Ultra-High Luminescence Saturation Threshold

In order to obtain novel and more efficient red light-emitting materials, a series of Sr2[Mg1-xLixAl5-xSixN7] : 0.01Eu2+ (SMAN-xLS, 0≤x≤0.5) red phosphors were devised and successfully synthesized via the high temperature solid state reaction and the effects of the co-substitution of [Mg-Al]5+ by [Li-Si]5+ on structural and luminescence properties is investigated in detail. A series of powder XRD data and Rietveld refinement indicate that [Li-Si]5+ co-substitution can successfully enter the Sr2[MgAl5N7] : 0.01Eu2+ (SMAN) lattice. With the entry of [Li-Si]5+ into the lattice, the substitution of Al3+ by Si4+ leads to the weakening of the nephelauxetic effect of the 5d level of Eu2+, which shifts the emission peak from 657 nm to 647 nm and reduces the excitation in the green region, i.e., lowers the absorption of green light. When the amount of [Li-Si]5+ co-substitution is x=0.1, the luminescence intensity and thermal stability of the sample are enhanced, in which the external quantum efficiency (EQE), reflecting the luminescence intensity, is elevated by 49.6 %. The increase in lattice rigidity gives rise to higher luminescence intensity, and the introduced trap levels for the compensation of luminescence enhances the thermal stability. Under blue laser excitation, the SMAN-0.1LS can achieve an ultra-high luminescence saturation threshold of 52.22 W/mm2, which is remarkably superior to other existing red phosphors, a breakthrough performance that has enormous potential for application in high-power laser display light sources. Cathodoluminescence (CL) characterization and measurements attest to the favorable CL properties of SMAN-0.1LS. By measuring the pressure-dependent luminescence of SMAN-0.1LS, the emission peak can be shifted from 650 nm to 702 nm with the increase of pressure, and the sensitivity dλ/dP is 5.07 nm/GPa, which is indicative of the potential application of this system as an optical pressure sensor.

Persistent Photoluminescence and Mechanoluminescence of a Highly Sensitive Pressure and Temperature Gauge in Combination with a 3D-Printable Optical Coding Platform

Distinct types of luminescence that are activated by various stimuli in a single material offer exciting developmental opportunities for functional materials. A versatile sensing platform that exhibits photoluminescence (PL), persistent luminescence (PersL), and mechanoluminescence (ML) is introduced, which enables the sensitive detection of temperature, pressure, and force/stress. The developed Sr2MgSi2O7:Eu2+/Dy3+ material exhibits a linear relationship between ML intensity and force and can be used as an ML stress sensor. Additionally, the bandwidth of the PL emission band and the PL lifetime of this material are remarkably sensitive to temperature, with values of ≈0.05 nm K-1 and 1.29%/K, respectively. This study demonstrates PersL pressure sensing for the first time, using long-lasting (seconds) lifetime as a manometric parameter. The developed material functions as an exceptionally sensitive triple-mode visual pressure sensor; specifically, it exhibits: i) a sensitivity of ≈-297.4 cm GPa-1 (8.11 nm GPa-1) in bandshift mode, ii) a sensitivity of ≈272.7 cm-1/GPa (14.8 nm GPa-1) in bandwidth mode, and iii) a sensitivity of 42%GPa-1 in PL-lifetime mode, which is the highest value reported to date. Notably, anti-counterfeiting, night-vision safety-sign, 8-bit optical-coding, and QR-code applications that exhibit intense PersL are demonstrated by 3D-printing the studied material in combination with a polymer.

Supersensitive visual pressure sensor based on the exciton luminescence of a perovskite material

Accurate, rapid, and remote detection of pressure, one of the fundamental physical parameters, is vital for scientific, industrial, and daily life purposes. However, due to the limited sensitivity of luminescent manometers, the optical pressure monitoring has been applied mainly in scientific studies. Here, we developed the first supersensitive optical pressure sensor based on the exciton-type luminescence of the Bi3+-doped, double perovskite material Cs2Ag0.6Na0.4InCl6. The designed luminescent manometer exhibits an extremely high sensitivity, i.e. dλ/dp = 112 nm GPa-1. It also allows multi-parameter sensing, using both blue-shift and rarely observed band narrowing with pressure. Importantly, this material has small temperature dependence for the manometric parameter used, i.e. spectral shift, allowing detection under extreme pressure and temperature conditions. The developed sensor operates in the visible range, and its emission shifts from orange to blue with pressure. This approach allowed us to demonstrate the real-world application of this sensor in detecting small changes in pressure with a designed uniaxial pressure device, with unprecedented resolution of the order of a few bars, demonstrating the technological potential of this sensor for remote, online monitoring of cracks and strains in heavy construction facilities.

Transparent nanocrystal-in-glass composite fibers for multifunctional temperature and pressure sensing

The pursuit of compact and integrated devices has stimulated a growing demand for multifunctional sensors with rapid and accurate responses to various physical parameters, either separately or simultaneously. Fluorescent fiber sensors have the advantages of robust stability, light weight, and compact geometry, enabling real-time and noninvasive signal detection by monitoring the fluorescence parameters. Despite substantial progress in fluorescence sensors, achieving multifunctional sensing in a single optical fiber remains challenging. To solve this problem, in this study, we present a bottom-up strategy to design and fabricate thermally drawn multifunctional fiber sensors by incorporating functional nanocrystals with temperature and pressure fluorescence responses into a transparent glass matrix. To generate the desired nanocrystal-in-glass composite (NGC) fiber, the fluorescent activators, incorporated nanocrystals, glassy core materials, and cladding matrix are rationally designed. Utilizing the fluorescence intensity ratio technique, a self-calibrated fiber sensor is demonstrated, with a bi-functional response to temperature and pressure. For temperature sensing, the NGC fiber exhibits temperature-dependent near-infrared emission at temperatures up to 573 K with a maximum absolute sensitivity of 0.019 K-1. A pressure-dependent upconversion emission is also realized in the visible spectral region, with a linear slope of -0.065. The successful demonstration of multifunctional NGC fiber sensors provides an efficient pathway for new paradigms of multifunctional sensors as well as a versatile strategy for future hybrid fibers with novel combinations of magnetic, optical, and mechanical properties.

Synthesis Design and Properties of Ca5(BO3)3F: Bi3+/Eu3+: Insight into Luminescence, Temperature, and Pressure Sensing

Nowadays, the utilization of noncontact temperature and pressure sensing is experiencing growing popularity. In this work, Bi3+, Eu3+-doped Ca5(BO3)3F (CBOF) phosphors were synthesized via an ionic liquid-assisted electrospinning approach. The effect of molecular weight of polyvinylpyrrolidone on the morphology of CBOF was investigated, and a comprehensive analysis of its formation mechanism was presented. The luminescence properties of CBOF: Bi3+, Eu3+ were studied systematically. The temperature-dependent emission of CBOF: Bi3+, Eu3+ phosphor was discussed, and it displayed thermal sensitivity, which can be attributed to the distinct thermal response emission behaviors of Bi3+ and Eu3+. The investigation of the pressure-dependent emission behavior of the CBOF: Bi3+ phosphor revealed an anomalous phenomenon: with the increase of pressure, the emission peak showed a trend of first a blue shift and then a red shift. This anomaly was discussed in detail. The phosphor exhibits visual color change (blue to cyan), remarkable pressure sensitivity (4.76 nm/GPa), and a high upper pressure limit (24.2 GPa), indicating its potential use as an optical pressure sensor. Consequently, this study presents an innovative synthetic approach for fabricating CBOF, presenting a bifunctional material with promising prospects in the fields of temperature and pressure sensing.

Ba3Lu(BO3)3:Ce3+,Tb3+/Mn2+: Dual-Functional Material for WLEDs and Optical Pressure Sensing

Ba3Lu(BO3)3(BLB):Ce3+,Tb3+/Mn2+ phosphors were designed to explore effective and multifunctional applications. Under the excitation of near-ultraviolet (n-UV) light, the BLB:Ce3+ phosphor showed broad-band blue emission. After codoping with Mn2+ ions, the single-phase white light phosphor is achieved through the energy transfer (ET) between Ce3+ and Mn2+. In addition, thermal stability is significantly enhanced by the addition of Tb3+ (BLB:0.02Ce3+,0.20Tb3+) compared to that codoped with Mn2+ (BLB:0.02Ce3+,0.10Mn2+). The light-emitting diode (LED) device with warm white light emission is fabricated with UV-chip-coated BLB:0.02Ce3+,0.05Tb3+ and Sr2Si5N8:Eu2+ phosphors, showing a good potential application value for LEDs. Additionally, the spectral properties of borate-based phosphors (BLB:0.02Ce3+) under high pressure were studied for the first time. Surprisingly, the change of pressure enabled the emission peak of BLB:0.02Ce3+ to be tuned from 485 to 552 nm, and dλ/dP is 3.51 nm GPa-1. The color changes from blue to yellow with an increase of pressure. Compared with the reported data, the pressure-sensing sensitivity based on the central peak shift in this work is the highest in all Ce3+ single-doped samples. In addition, the emitting color and intensity were gradually regained after decompression. The intensity can reach 80% of the initial intensity. All data demonstrate that the BLB:0.02Ce3+ phosphor has the potential to be utilized as an optical pressure sensor due to the high-pressure sensitivity and visible color tuning.

Pressure-Induced Remarkable Spectral Red-Shift in Mn2+ -Activated NaY9 (SiO4 )6 O2 Red-Emitting Phosphors for High-Sensitive Optical Manometry

To settle the low sensitivity of luminescent manometers, the Mn2+ -activated NaY9 (SiO4 )6 O2 red-emitting phosphors with splendid pressure sensing performances are developed. Excited by 408 nm, the resulting products emit bright red emission originating from 4 T1 (4 G) → 6 A1 transition of Mn2+ , in which the optimal concentration of the activator ion is ≈1 mol%. Moreover, the admirable thermal stability of the developed phosphors is studied and confirmed by the temperature-dependent emission spectra, based on which the activation energy is derived to be 0.275 eV. By analyzing the pressure-dependent Raman spectra, the structural stability of the synthesized compounds at extreme conditions is verified. Furthermore, the designed phosphors exhibit remarkable spectral red-shift at elevated pressure. Especially, as pressure increases from 0.75 to 7.16 GPa, the emission band centroid shifts from 617.2 to 663.4 nm, resulting in a high sensitivity (dλ/dP) of 7.00 nm GPa-1 , whereas the full width at half maximum (FWHM) increases from 83.0 to 110.6 nm, leading to the ultra-high sensitivity (dFWHM/dP) of 10.13 nm GPa-1 . These achievements manifest that the designed red-emitting phosphors are appropriate for ultrasensitive optical manometry. More importantly, the developed manometer is a current global leader in sensitivity, when operating in the band-width mode, that is, FWHM.

Pressure-Triggered Fluorescence Intensity Ratio Variations of YNbO4:Bi3+/Ln3+ (Ln = Eu or Sm) for High-Sensitivity Optical Pressure Sensing

Optical pressure sensing by phosphors is a growing area of research. However, the main pressure measurement methods rely on the movement of the central peak position, which has significant drawbacks for practical applications. This paper demonstrates the feasibility of using the fluorescence intensity ratio (FIR) of different emission peaks for pressure sensing. The FIR (IBi3+/ILn3+) values of the synthesized YNbO4:Bi3+/Ln3+ (Ln = Eu or Sm) phosphors are all first-order exponentially related to pressure, and YNbO4:Bi3+/Ln3+ (Ln = Eu or Sm) phosphors have high pressure-sensing sensitivities (Sp and Spr), which are 6 times higher than those from our previously reported work. In addition, the changes in FIR values during the decompression process were also calculated, and the trend was similar to that during the compression process. The YNbO4:Bi3+,Eu3+ phosphor has better pressure recovery performance. In summary, the YNbO4:Bi3+/Ln3+ (Ln = Eu or Sm) phosphors reported in this paper are expected to be applied in the field of optical pressure sensing, and this study provides a new approach and perspective for designing new phosphors for pressure measurement.

Ce3+-Doped Li2Ca5Gd(BO3)5 Phosphors with Multiple Luminescent Centers and High Pressure Sensitivity under Near UV Excitation

The performance of Ce3+-based phosphors under mechanical high pressures becomes attractive due to the potential application as a visual pressure sensor. Li2Ca5Gd(BO3)5 was selected as the host for the Ce3+ doping. Rietveld refinements reveal that rare earth cations occupy M1, M2, and M3 sites, and indeed, the photoluminescent spectra of Li2Ca5Gd1-xCex(BO3)5 (0.005 ≤ x ≤ 0.15) exhibit the characteristic of multiple activators, defined as CeI, CeII, and CeIII, with the maximal emission wavelength at ∼444, 419, and 378 nm, respectively. The optimal internal and external quantum efficiencies are 86.29% for x = 0.005 and 20.26% for x = 0.10, respectively, under the NUV excitation at 363 nm. In-situ high pressure emission spectra under 375 nm excitation exhibit an overall red-shift, and the linear pressure susceptibilities up to 6.7 GPa for CeI and CeII centers are -390 and -279 cm-1/GPa, respectively, which is probably the largest among Ce3+-doped oxides and oxysalts. Due to the above superiorities, Ce3+-doped LCGB possesses a high potential as a visual pressure sensor, and this is a successful study on the structure-property relationship of inorganic materials.

Calibration of local chemical pressure by optical probe

Chemical stabilization of a high-pressure metastable state is a major challenge for the development of advanced materials. Although chemical pressure (Pchem) can effectively simulate the effect of physical pressure (Pphy), experimental calibration of the pressure passed to local structural motifs, denoted as local chemical pressure (Pchem-Δ) which significantly governs the function of solid materials, remains absent due to the challenge of probing techniques. Here we establish an innovative methodology to experimentally calibrate the Pchem-Δ and build a bridge between Pchem and Pphy via an optical probe strategy. Site-selective Bi3+-traced REVO4 (RE = Y, Gd) is adopted as a prototype to introduce Bi3+ optical probes and on-site sense of the Pchem-Δ experienced by the REO8 motif. The cell compression of RE0.98Bi0.02VO4 under Pphy is chemically simulated by smaller-ion substitution (Sc3+ → RE3+) in RE0.98-xScxBi0.02VO4. The consistent red shift (Δλ) of the emission spectra of Bi3+, which is dominated by locally pressure-induced REO8 dodecahedral variation in RE0.98Bi0.02VO4 (Pphy) and RE0.98-xScxBi0.02VO4 (Pchem-Δ), respectively, is evidence of their similar pressure-dependent local structure evolution. This innovative Δλ-based experimental calibration of Pchem-Δ in the crystal-field dimension portrays the anisotropic transmission of Pchem to the local structure and builds a bridge between Pchem-Δ and Pphy to guide a new perspective for affordable and practical interception of metastable states.

Lanthanide molecular cluster-aggregates as the next generation of optical materials

In this perspective, we provide an overview of the recent achievements in luminescent lanthanide-based molecular cluster-aggregates (MCAs) and illustrate why MCAs can be seen as the next generation of highly efficient optical materials. MCAs are high nuclearity compounds composed of rigid multinuclear metal cores encapsulated by organic ligands. The combination of high nuclearity and molecular structure makes MCAs an ideal class of compounds that can unify the properties of traditional nanoparticles and small molecules. By bridging the gap between both domains, MCAs intrinsically retain unique features with tremendous impacts on their optical properties. Although homometallic luminescent MCAs have been extensively studied since the late 1990s, it was only recently that heterometallic luminescent MCAs were pioneered as tunable luminescent materials. These heterometallic systems have shown tremendous impacts in areas such as anti-counterfeiting materials, luminescent thermometry, and molecular upconversion, thus representing a new generation of lanthanide-based optical materials.

Eu2+-Doped Ca4Y3Si7O15N5 Phosphor with High Thermal Stability and Pressure Sensitivity for Dual-Functional Applications in W-LEDs and Pressure Sensors

A novel green-light-emitting silicon-based oxynitride phosphor Ca₄Y₃Si₇O₁₅N₅:Eu²⁺ with low thermal quenching and ideal pressure sensitivity is reported. The Ca_3.99Y₃Si₇O₁₅N₅:0.01Eu²⁺ phosphor can be efficiently excited by 345 nm ultraviolet light and shows very low thermal quenching (integrated and peak emission intensities at 373 and 423 K were 96.17, 95.86, and 92.73, 90.66% of those at 298 K, respectively). The correlation between high thermal stability and structural rigidity is investigated in detail. The white-light-emitting diode (W-LED) is assembled by depositing the obtained green-light-emitting phosphor Ca_3.99Y₃Si₇O₁₅N₅:0.01Eu²⁺ and commercial phosphors on a ultraviolet (UV)-emitting chip (λ = 365 nm). The CIE color coordinates, color rendering index (Ra), and corrected color temperature (CCT) of the obtained W-LED are (0.3724, 0.4156), 92.9, and 4806 K, respectively. In addition, when subjected to in situ high-pressure fluorescence spectroscopy, the phosphor exhibits an evident red shift of 40 nm with an increase in pressure from 0.2 to 32.1 GPa. The phosphor has the advantage of high-pressure sensitivity (dλ/dP = 1.13 nm GPa^-1) and visualization with pressure changes. The possible reasons and mechanisms are deeply discussed in detail. Based on the above advantages, Ca_3.99Y₃Si₇O₁₅N₅:0.01Eu²⁺ phosphor is expected to have potential applications in W-LEDs and optical pressure sensing.

Morphological Engineering of Sensing Materials for Flexible Pressure Sensors and Artificial Intelligence Applications

Various morphological structures in pressure sensors with the resulting advanced sensing properties are reviewed comprehensively. Relevant manufacturing techniques and intelligent applications of pressure sensors are summarized in a complete and interesting way. Future challenges and perspectives of flexible pressure sensors are critically discussed.

As an indispensable branch of wearable electronics, flexible pressure sensors are gaining tremendous attention due to their extensive applications in health monitoring, human –machine interaction, artificial intelligence, the internet of things, and other fields. In recent years, highly flexible and wearable pressure sensors have been developed using various materials/structures and transduction mechanisms. Morphological engineering of sensing materials at the nanometer and micrometer scales is crucial to obtaining superior sensor performance. This review focuses on the rapid development of morphological engineering technologies for flexible pressure sensors. We discuss different architectures and morphological designs of sensing materials to achieve high performance, including high sensitivity, broad working range, stable sensing, low hysteresis, high transparency, and directional or selective sensing. Additionally, the general fabrication techniques are summarized, including self-assembly, patterning, and auxiliary synthesis methods. Furthermore, we present the emerging applications of high-performing microengineered pressure sensors in healthcare, smart homes, digital sports, security monitoring, and machine learning-enabled computational sensing platform. Finally, the potential challenges and prospects for the future developments of pressure sensors are discussed comprehensively.

An efficient blue phosphor with high thermal stability for lighting and optical pressure sensor applications

For exploring new and efficient luminescent materials, we developed an efficient narrow-band blue-emitting phosphor Eu2+ doped Na3CsMg7(PO4)6. Under near-ultraviolet light excitation, the phosphor can emit bright blue light with narrow...

Responsive Sensors of Upconversion Nanoparticles

Upconversion nanoparticles are a class of luminescent materials that convert longer-wavelength near-infrared photons into visible and ultraviolet emissions. They can respond to various external stimuli, which underpins many opportunities for developing the next generation of sensing technologies. In this perspective, the unique stimuli-responsive properties of upconverting nanoparticles are introduced, and their recent implementations in sensing are summarized. Promising material development strategies for enhancing the key sensing merits, including intrinsic sensitivity, biocompatibility and modality, are identified and discussed. The outlooks on future technological developments, novel sensing concepts, and applications of nanoscale upconversion sensors are provided.

NIR emission of lanthanides for ultrasensitive luminescence manometry-Er3+-activated optical sensor of high pressure

Pressure is an important physical parameter and hence its monitoring is very important for different industrial and scientific applications. Although commonly used luminescent pressure sensors (ruby-Al₂O₃:Cr³⁺ and SrB₄O₇:Sm²⁺) allow optical monitoring of pressure in compressed systems (usually in a diamond anvil cell; DAC), their detection resolution is limited by sensitivity, i.e., pressure response in a form of the detected spectral shift. Here we report, a breakthrough in optical pressure sensing by developing an ultra-sensitive NIR pressure sensor (dλ/dP = 1.766 nm GPa^-1). This luminescent manometer is based on the optically active YVO₄:Yb³⁺-Er³⁺ phosphor material which exhibits the largest spectral shift as a function of pressure compared to other luminescent pressure gauges reported elsewhere. In addition, thanks to the locations of excitation and emission in the NIR range, the developed optical manometer allows high-pressure measurements (without spectral overlapping/interferences) of various luminescent organic and inorganic materials, which are typically excited and can emit in the UV-vis spectral ranges.

Optical pressure and temperature sensing properties of Nd3+:YTaO4

The pressure- and temperature-dependent luminescence properties of M'-phase Nd³⁺:YTaO₄ synthesized by a molten salt method are presented. Ten near-infrared emission lines originating from the transitions between the two Stark levels R_1,2 of the ³F_3/2 state and the five Stark levels Z_1,2,3,4,5 of the ⁴I_9/2 state for the doped Nd³⁺ ions can be clearly identified. All these emission lines are found to shift linearly with pressure in a range up to ∼11 GPa. The R_2,1 → Z₅ emission lines have larger pressure sensitivities, which are 16.44 and 14.27 cm^-1 GPa^-1. The intensities of all the emission lines evolve with pressure non-monotonically, and peak at ∼1 GPa. The R₁ → Z_4,5 and R₂ → Z₁ emission lines can be obviously narrowed under the hydrostatic pressure, and broadened under the non-hydrostatic pressure, indicating their potential capability for reflecting the characteristic of a pressure environment. The intensity ratio of the R_2,1 → Z₅ emission lines exhibits a large temperature dependence, with a relative sensitivity between 0.129% and 0.108% K^-1 in the physiological temperature range of 290-320 K. Thermal variations of the spectral positions and widths of the R_2,1 → Z₅ emission lines are also investigated. A high thermal stability for the position of the R₂ → Z₅ emission line is revealed. Based on the experimental results, the advantages and potential of Nd³⁺:YTaO₄ as a multi-functional sensor for pressure and temperature are discussed.

Pressure-Induced Emission toward Harvesting Cold White Light from Warm White Light

The pressure-induced emission (PIE) behavior of halide perovskites has attracted widespread attention and has potential application in pressure sensing. However, high-pressure reversibility largely inhibits practical applications. Here, we describe the emission enhancement and non-doping control of the color temperature in two-dimensional perovskite (C₆ H₅ CH₂ CH₂ NH₃ )₂ PbCl₄ ((PEA)₂ PbCl₄ ) nanocrystals (NCs) through high-pressure processing. A remarkable 5 times PIE was achieved at a mild pressure of 0.4 GPa, which was highly associated with the enhanced radiative recombination of self-trapped excitons. Of particular importance is the retention of the 1.6 times emission of dense (PEA)₂ PbCl₄ NCs upon the complete release of pressure, accompanied by a color change from "warm" (4403 K) to "cold" white light with 14295 K. The irreversible pressure-induced structural amorphization, which facilitates the remaining local distortion of inorganic Pb-Cl octahedra with respect to the steric hindrance of organic PEA⁺ cations, should be greatly responsible for the quenched high-efficiency photoluminescence.

Lanthanide-Based Nanosensors: Refining Nanoparticle Responsiveness for Single Particle Imaging of Stimuli

Lanthanide nanoparticles (LNPs) are promising sensors of chemical, mechanical, and temperature changes; they combine the narrow-spectral emission and long-lived excited states of individual lanthanide ions with the high spatial resolution and controlled energy transfer of nanocrystalline architectures. Despite considerable progress in optimizing LNP brightness and responsiveness for dynamic sensing, detection of stimuli with a spatial resolution approaching that of individual nanoparticles remains an outstanding challenge. Here, we highlight the existing capabilities and outstanding challenges of LNP sensors, en-route to nanometer-scale, single particle sensor resolution. First, we summarize LNP sensor read-outs, including changes in emission wavelength, lifetime, intensity, and spectral ratiometric values that arise from modified energy transfer networks within nanoparticles. Then, we describe the origins of LNP sensor imprecision, including sensitivity to competing conditions, interparticle heterogeneities, such as the concentration and distribution of dopant ions, and measurement noise. Motivated by these sources of signal variance, we describe synthesis characterization feedback loops to inform and improve sensor precision, and introduce noise-equivalent sensitivity as a figure of merit of LNP sensors. Finally, we project the magnitudes of chemical and pressure stimulus resolution achievable with single LNPs at nanoscale resolution. Our perspective provides a roadmap for translating ensemble LNP sensing capabilities to the single particle level, enabling nanometer-scale sensing in biology, medicine, and sustainability.

High-resolution integrated piezoresistive sensors for microfluidic monitoring

Microfluidic devices are traditionally monitored by bulky and expensive off-chip sensors. We have developed a soft piezoresistive sensor capable of measuring micron-level strains that can be easily integrated into devices via soft lithography. We apply this sensor to achieve fast and localized monitoring of pressure, flow, and valve actuation.

Diverse physical functionalities of rare-earth hexacyanidometallate frameworks and their molecular analogues

The combination of rare-earth metal complexes and hexacyanidometallates of transition metals is a fruitful pathway for achieving functional materials exhibiting a wide scope of mechanical, magnetic, optical, and electrochemical properties.

Pressure-Dependent Behavior of Defect-Modulated Band Structure in Boron Arsenide

The recent observation of unusually high thermal conductivity exceeding 1000 W m^-1 K^-1 in single-crystal boron arsenide (BAs) has led to interest in the potential application of this semiconductor for thermal management. Although both the electron/hole high mobilities have been calculated for BAs, there is a lack of experimental investigation of its electronic properties. Here, a photoluminescence (PL) measurement of single-crystal BAs at different temperatures and pressures is reported. The measurements reveal an indirect bandgap and two donor-acceptor pair (DAP) recombination transitions. Based on first-principles calculations and time-of-flight secondary-ion mass spectrometry results, the two DAP transitions are confirmed to originate from Si and C impurities occupying shallow energy levels in the bandgap. High-pressure PL spectra show that the donor level with respect to the conduction band minimum shrinks with increasing pressure, which affects the release of free carriers from defect states. These findings suggest the possibility of strain engineering of the transport properties of BAs for application in electronic devices.

Pressure-induced variation of persistent luminescence characteristics in Y3Al5-xGaxO12:Ce3+-M3+ (M = Yb, and Cr) phosphors: opposite trend of trap depth for 4f and 3d metal ions

Changing the electronic structure of materials by pressure and the accompanying changes in optical properties have attracted scientific interest. We have reported that the energy position of the conduction band (CB) bottom and the crystal field splitting of the Ce3+:5d excited level in Y3Al5-xGaxO12:Ce3+ are changed by applying pressure, which results in the red shifting of the Ce3+:5d → 4f luminescence and the increase of the quenching temperature. We also reported dramatic improvement of the persistent luminescence performance by either Cr3+ or Yb3+ codoping into the Y3Al5-xGaxO12:Ce3+ phosphors. The different trap depths formed by Cr3+ and Yb3+ affect the initial persistent luminescence intensity and the persistent luminescence duration. In this study, the effect of pressure on the persistent luminescence performance was investigated. For the Y3AlGa4O12:Ce3+-Yb3+ phosphor, the slope of persistent luminescence decay curve becomes more gentle with increasing pressure, while for the Y3AlGa4O12:Ce3+-Cr3+ phosphor the slope becomes steeper. These results indicate that the trap depth of Yb3+ becomes deeper and that of Cr3+ becomes shallower with increasing pressure. Based on the pressure-dependence of the luminescence quenching and the trap depth change estimated from the decay slopes, the relative electronic energies of the CB bottom and the Yb2+ (4f14) or Cr2+ (3d4) levels are discussed. The CB bottom energy is increased relative to the ground 1S0 state of Yb2+ with increasing pressure, which results in deepening of the electron trap depth of the Yb2+ state. The opposite tendency of the Cr3+ codoped sample was described by a decreasing tendency of the energy gap between the CB bottom and the Cr2+:eg level, the relative energy level of which is increased by the increase of the crystal field with increasing pressure in the garnet host material, where the electron-trapping Cr2+ ions take the high spin state (t32ge1g) rather than the low-spin state (t42g).

Lanthanide Upconverted Luminescence for Simultaneous Contactless Optical Thermometry and Manometry-Sensing under Extreme Conditions of Pressure and Temperature

The growing interest in the miniaturization of various devices and conducting experiments under extreme conditions of pressure and temperature causes the need for the development of small, contactless, precise, and accurate optical sensors without any electrical connections. In this work, YF₃:Yb³⁺-Er³⁺ upconverting microparticles are used as a bifunctional luminescence sensor for simultaneous temperature and pressure measurements. Different changes in the properties of Er³⁺ green and red upconverted luminescence, after excitation of Yb³⁺ ions in the near-infrared at ∼975 nm, are used to calibrate pressure and/or temperature inside the hydrostatic chamber of a diamond anvil cell (DAC). For temperature sensing, changes in the relative intensities of the Er³⁺ green upconverted luminescence of ²H_11/2 and ⁴S_3/2 thermally coupled multiplets to the ⁴I_15/2 ground state, whose relative populations follow a Boltzmann distribution, are calibrated. For pressure sensing, the spectral shift of the Er³⁺ upconverted red emission peak at ∼665 nm, between the Stark sublevels of the ⁴F_9/2 → ⁴I_15/2 transition, is used. Experiments performed under simultaneous extreme conditions of pressure, up to ∼8 GPa, and temperature, up to ∼473 K, confirm the possibility of remote optical pressure and temperature sensing.

Micro-Fabricated Presure Sensor Using 50 nm-Thick of Pd-Based Metallic Glass Freestanding Membrane

This paper reports on micro-fabricated pressure sensors based on a thin metallic glass membrane. The Pd₆₆Cu₄Si₃₀ metallic glass material is deposited successfully by a sputter technique. An amorphous feature of the deposited film is confirmed by high resolution transmission electron microscopy (HR-TEM) and the corresponding the selected area electron diffraction (SAED). The ultra-flat freestanding metallic glass membrane with 50 nm in thickness and 2 mm in circular diameter has been fabricated successfully. In addition, two kinds of micro-fabricated pressure sensor types, including itself membrane and additional metallic glass bar as piezoresistive sensing elements, are proposed and fabricated. A displacement of membrane can reach over 100 µm without any damage to membrane which is equivalent to over 0.7% of an elastic strain. Besides, the temperature coefficient of resistance of the Pd-based metallic glass thin film is extremely low 9.6 × 10^-6 °C^-1. This development of nano-thick metallic glass membrane possibly opens a new field of micro-fabricated devices with large displacement and enhanced sensing.

High pressure induced local ordering and tunable luminescence of La2Hf2O7:Eu3+ nanoparticles

This work highlights the high-pressure induced site swapping and improved ordering of Eu³⁺ in La₂Hf₂O₇:Eu³⁺ nanocrystals which leads to red-orange-yellow tunable emission at low-moderate-high pressure regime and enhanced correlated color temperature.

New phenomena of photo-luminescence and persistent luminescence of a Eu2+,Tb3+ codoped Ca6BaP4O17 phosphor under high hydrostatic pressure

The possibility of regulating the photo luminescence and persistent luminescence performances of Ca₆BaP₄O₁₇:Eu²⁺,Tb³⁺ under high hydrostatic pressure.

UV-Vis-NIR absorption spectra of lanthanide oxides and fluorides

Absorption spectra of inorganic lanthanide fluorides and oxides.

Upconverting Lanthanide Fluoride Core@Shell Nanorods for Luminescent Thermometry in the First and Second Biological Windows: β-NaYF4:Yb3+- Er3+@SiO2 Temperature Sensor

Upconverting core@shell type β-NaYF₄:Yb³⁺-Er³⁺@SiO₂ nanorods have been obtained by a two-step synthesis process, which encompasses hydrothermal and microemulsion routes. The synthesized nanomaterial forms stable aqueous colloids and exhibits a bright dual-center emission (λ_ex = 975 nm), i.e., upconversion luminescence of Er³⁺ and down-shifting emission of Yb³⁺, located in the first (I-BW) and the second (II-BW) biological windows of the spectral range, respectively. The intensity ratios of the emission bands of Er³⁺ and Yb³⁺ observed in the vis-near-infrared (NIR) range monotonously change with temperature, i.e., the thermalized Er³⁺ levels (²H_11/2 → ⁴I_15/2/⁴S_3/2 → ⁴I_15/2) and the nonthermally coupled Yb³⁺/Er³⁺ levels (²F_5/2 → ²F_7/2/⁴I_9/2 → ⁴I_15/2 or ⁴F_9/2 → ⁴I_15/2). Hence, their thermal evolutions have been correlated with temperature using the Boltzmann type distribution and second-order polynomial fits for temperature-sensing purposes, i.e., Er³⁺ 525/545 nm (max S_r = 1.31% K^-1) and Yb³⁺/Er³⁺ 1010/810 nm (1.64% K^-1) or 1010/660 nm (0.96% K^-1). Additionally, a fresh chicken breast was used as a tissue imitation in the performed ex vivo experiment, showing the advantage of the use of NIR Yb³⁺/Er³⁺ bands, vs. the typically used Er³⁺ 525/545 nm band ratio, i.e., better penetration of the luminescence signal through the tissue in the I-BW and II-BW. Such nanomaterials can be utilized as accurate and effective, broad-range vis-NIR optical, contactless sensors of temperature.

Structure and luminescence properties of multicolor phosphor Ba2La3(GeO4)3F:Tb3+,Eu3+

A new kind of multicolor phosphor Ba₂La₃(GeO₄)₃F:0.15Tb³⁺,xEu³⁺ (BLGOF:0.15Tb³⁺,xEu³⁺) has been acquired through the traditional high temperature solid phase synthesis method. The structural information of the phosphor was studied by X-ray diffraction (XRD), scanning electron microscopy (SEM) and Rietveld refinement. The optical properties of the phosphor have also been studied in detail, including its photoluminescence spectra (PL), photoluminescence excitation spectra (PLE), fluorescence decay curves, energy transfer mechanism and thermal quenching spectra. It has been found that the optimum concentration of Eu³⁺ in BLGOF:0.15Tb³⁺,xEu³⁺ is 0.24 mol and the energy transfer mechanism from Tb³⁺ to Eu³⁺ in BLGOF is quadrupole–quadrupole. The color of BLGOF:0.15Tb³⁺,xEu³⁺ phosphors can be changed from green to yellow/orange to red. Some details of the energy transfer are reviewed and the effect of complex anion regulation on thermal stability has also been studied. All the properties are good and can contribute to the promotion from the laboratory to practical application for the phosphor.

Single-phase Ba₂La₃(GeO₄)₃F:Tb³⁺,Eu³⁺ phosphors were obtained for the first time.

Enhanced photoluminescence and thermal stability in solid solution Ca1−xSrxSc2O4:Ce3+ (x = 0–1) via crystal field regulation and site-preferential occupation

Enhanced photoluminescence efficiency and thermal stability as well as controllable blue-green tuning of solid solution Ca_1−xSr_xSc₂O₄:Ce³⁺ phosphors were realized based on crystal field regulation and site-preferential occupation.