Mechanoluminescence Research Articles

Multiple Defect-Induced High-Resolution Near-Infrared Mechanoluminescent Materials for Non-Destructive Detection of Blood Glucose and Lipids.

Mechanoluminescence (ML) materials, known for their ability to convert mechanical energy into light, are increasingly recognized for their potential applications, such as in intelligent stress sensing, in vivo bioimaging, and stress non-destructive monitoring. However, the low signal-to-noise ratio (SNR) and narrow-band emission of single-defect-induced ML materials usually limit their biological-related practical applications. Here, these limitations will be addressed by modulating the microstructure evolution in Y3Ga3MgSiO12:Cr3+ through the [Si4++Mg2+] → [Ga3++Ga3+] chemical substitution strategy. Density functional theory (DFT) calculation reveals the defect types and dynamic charge migration processes. In addition, Y3Ga3MgSiO12: Cr3+ with continuously distributed "shallow-deep" defects (0.68-1.61eV) can avoid persistent luminescence (PersL) and bright-field environment interference. Herein, such high SNR near-infrared broadband ML emission may provide a reliable way for high-quality biological non-destructive sensing and detection. Finally, benefiting from the different absorption of ML signals in glucose/lipid, one may find a novel non-invasive blood glucose/lipid testing technology in patients.

Ultraviolet light charged and self-powered mechanoluminescence of KMgF3: Tb3+ glass ceramics in various media

The light waveguiding effect of transparent glass ceramics (GCs) on mechanoluminescence (ML) signals is highly attractive for remote stress sensing and structural health monitoring applications. However, a prerequisite for generating ML in GCs is pre-irradiation with high-energy rays, which not only increases application costs but also poses a risk of GCs devitrification. Herein, we propose a safe, non-destructive, and convenient charging method for the ML of KMgF3: Tb3+ GCs, namely ultraviolet (UV) light charging. By effectively filling the intrinsic defects in KMgF3: Tb3+ nanocrystal using UV light, we achieved trap-controlled ML in rigid GCs. Moreover, this ML is attributed to thermoluminescence (TL) induced by frictional heating during mechanical stimulation. Additionally, when the GCs powder is combined with flexible polydimethylsiloxane (PDMS), a self-powered (without any pre-charging) ML induced by interfacial triboelectricity can also be achieved, which is similar to the results observed in most flexible ML systems. This work proposes a more straightforward and safer approach for applications such as mechanical sensing based on the ML of transparent GCs.

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 ≈0.05nmK-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 ≈-297.4cmGPa-1 (8.11nmGPa-1) in bandshift mode, ii) a sensitivity of ≈272.7cm-1/GPa (14.8nmGPa-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.

Mechanoluminescent/Electric Dual-Mode Sensors Enabled by Trace Carbon Nanotubes.

Mechanoluminescence (ML)-based sensors are emerging as promising wearable devices, attracting attention for their self-powered visualization of mechanical stimuli. However, challenges such as weak brightness, high activation threshold, and intermittent signal output have hindered their development. Here, a mechanoluminescent/electric dual-mode strain sensor is presented that offers enhanced ML sensing and reliable electrical sensing simultaneously. The strain sensor is fabricated via an optimized dip-coating method, featuring a sandwich structure with a single-walled carbon nanotube (SWNT) interlayer and two polydimethylsiloxane (PDMS)/ZnS:Cu luminescence layers. The integral mechanical reinforcement framework provided by the SWNT interlayer improves the ML intensity of the SWNT/PDMS/ZnS:Cu composite film. Compared to conventional nanoparticle fillers, the ML intensity is enhanced nearly tenfold with a trace amount of SWNT (only 0.01wt.%). In addition, the excellent electrical conductivity of SWNT forms a conductive network, ensuring continuous and stable electrical sensing. These strain sensors enable comprehensive and precise monitoring of human behavior through both electrical (relative resistance change) and optical (ML intensity) methods, paving the way for the development of advanced visual sensing and smart wearable electronics in the future.

Piezoelectric-induced mechanoluminescence in centrosymmetric Lu3Al5O12: Properties of self-recoverable and tunable near-infrared luminescence

Mechanoluminescence (ML) materials with long-wavelength emission bands are essential for future in vivo bioimaging, non-destructive testing. However, most of the near-infrared (NIR) ML materials require pre-irradiation, which may limit their further applications. Generally, piezoelectric-induced ML materials were considered to be related to the piezoelectric effect from non-centrosymmetric structure. Innovatively in this work, a novel piezoelectric-induced near-infrared ML material Lu3Al5O12:Cr3+ with centrosymmetric structure is obtained. In Lu3Al5O12:Cr3+, piezoelectric effect is generated from the distortion of the centrosymmetric structure of the host due to the uneven electron distribution of Cr3+. Here, highly tunable ML FWHM from 7 nm to 118 nm is realized by introducing different content Ga3+ ions to Lu3Al5O12:Cr3+. The ML film fabricated by composite polydimethylsiloxane and Lu3Al2Ga3O12:Cr3+ can penetrate 20 mm pork tissue, which suggests the potential applications of the NIR ML material in the field of optical imaging of stress distribution in organisms. The discovery of distorted crystal structure to induce piezoelectric effect provides a new thinking for exploring ML in centrosymmetric materials. In addition, LuAl5-xGaxO:Cr3+ phosphors have broad prospects in self-powered sensing, temporomandibular disorders diagnosis, information security, and biomedical fields.

Simultaneous Triboelectric and Mechanoluminescence Sensing Toward Self‐Powered Applications

AbstractSimultaneous phenomena of triboelectricity and mechanoluminescence (ML) acquire vital insights into the mechanics of charge separation and recombination, as well as the relationship between mechanical stress and light emission. In the present work, polydimethylsiloxane (PDMS) and ZnS:Cu particle‐based composites are fabricated, which have good ML characteristics and can generate electricity via contact electrification. ML, in conjunction with a triboelectric nanogenerator (TENG), contributes by producing power from mechanical operations while also giving vital visual input in the form of light emission. This dual capability improves user awareness and efficiency in a variety of applications, making mechanical systems and wearable devices easier to monitor and optimize. To accomplish this, a single‐electrode mode silver (Ag) nanowires embedded PDMS‐ZnS: Cu‐based TENG device is developed and achieved an electrical output of 60 V, 395 nA, and 15 nC by using a linear motor. Furthermore, the combined ML and TENG device is employed in various cases of safety monitoring. This integration provides self‐powered devices that detect mechanical stress, delivering real‐time warnings and illumination signals for increased safety and communication in demanding conditions such as SOS signaling, underwater driving, deep mining, and sports.

Suppressed emission intensity of mechanoluminescence film on steel

The emission intensity from mechanoluminescence (ML) film (SrAl2O4:Eu2+) on a steel was lower than that on an aluminum alloy. The phenomenon was confirmed by utilizing detachable ML films where two films with identical properties were adhered to testpieces of dissimilar materials. The ML intensity from the one adhered on an Al-Mg-Si alloy testpiece was six times higher than that from the other on a ferric stainless steel testpiece, under the identical tensile testing conditions. Furthermore, the stainless steel testpiece, of which only single side was adhered with an aluminum foil, was prepared, the ML tests were held on both sides with the same detachable ML films. As the result, the intensity from the aluminum side showed more than twice than that from the other side without aluminum. Therefore, it is newly found suppressed ML performance on steel sheet can be avoided with the aluminum insert.

Lead-Free Perovskite With Efficient Tellurium Ion Activation for Multifunctional Applications.

Lead-free perovskite materials have received extensive attention due to their non-toxicity, super environmental stability and adjustable photoelectric properties. However, the inherent problems of low luminous efficiency and low photoluminescence quantum yields (PLQYs) limit its development in multifunctional applications. Here, Te4+ doped Cs2ZrCl6 with high luminous efficiency and stability for multifunctional applications are developed. Te4+ ions are used as emission centers to improve the optical properties of Cs2ZrCl6 to make efficient and stable single-component white light-emitting diodes (WLEDs), and can be used as scintillator materials to improve scintillation performance to achieve high-resolution and low-dose X-ray imaging detection. In addition, it is found for the first time that Te4+ ions can be introduced into the trap center, so that the Cs2ZrCl6:Te4+ perovskite material exhibits excellent persistent luminescence (PersL) and mechanoluminescence (ML) after X-ray radiation, which has potential applications in the fields of delayed imaging and stress sensing. This work provides a method for designing lead-free perovskites with high optical performance and scintillating properties, as well as developing multifunctional applications.

Deeply trapped electrons induced long-time sustainable mechanoluminescence of X-ray irradiated La2Ti2O7:Pr3+ for detection of stress burst

X-ray irradiated La2Ti2O7:Pr3+ was found to show long-time sustainable mechanoluminescence (ML), which can realize the high sensitivity and real time detection of stress burst for more than 72 h. Under the excitation of X-ray, La2Ti2O7:Pr3+ shows red ML emissions located at 610, 624 and 638 nm, which are similar to the afterglow emission spectrum and can be ascribed to1D2-3H4, 3P0-3H4 and 3P0-3H2 of Pr3+. And the linear increases of compressive load can induce the linear increases of ML intensity of the sample, indicating that the X-ray induced ML emission can be utilized to accurately detect the stress applied on the object. Furthermore, X-ray irradiated La2Ti2O7:Pr3+ possesses excellent stability and the repeatability of ML emission and the ML signals can keep stable even 50 load cycles after 1 h decay. The thermoluminescence results suggest that abundant electrons are trapped in shallow and deep answered for stable ML emission. More importantly, the deeply trapped electrons induced ML emissions from X-ray irradiated La2Ti2O7:Pr3+ can be utilized to detect the stress bursts for a long time. When the sample is recharged by 5 min X-ray irradiation once, within 24 h decay, the 1500 N burst among many 1000 N cycles can be clearly detected, and the signal to noise ratio (S/N) reaches 1.32 and 1.26 after 12 and 24 h decay, respectively. And even after 72 h decay, the S/N of 2500 N still arrives at 1.23 and that of 4000 N reaches 1.97, indicative of long-time high sensitivity detection of abnormal stress. All these results suggest that the X-ray-irradiated La1.97Ti2O7:0.03Pr3+/resin sample can realize the high sensitivity and real time detection of stress burst for more than 72 h, which thus possesses great potential application in early warning of the emergency disasters such as bridge fracture, tunnel collapse and so on.

A perspective on mechanoluminescence and multipiezo in ferroelectric materials

The discovery of innovative mechanoluminescence materials of SrAl2O4 and ZnS, which emit repeatable light [repeatable mechanoluminescence (ML), hereafter simply ML] even by soft touch, has trigged intense research interest in material/device/system development for applications across various fields. This perspective presents an overview of the crystal structures, mechanisms, and ML behaviors of most promising systems, namely, SrAl2O4-, ZnS-, LiNbO3-, and Sr3Sn2O7-based ferroelectric materials. These multipiezo materials, which simultaneously exhibit intrinsic piezoluminescence (true elastic deformation induced ML and no friction effect) and piezoelectricity, show distinct and valuable characteristics by integrating mechanical force, electric field, and light for stress sensing and other applications. Recent studies indicated the critical role of crystal structure, doping, and piezoelectric properties in achieving robust and reliable ML performance. These findings suggest that ML materials hold substantial promise for applications in stress/force sensing, structural health monitoring, mechanically activated lighting, and advanced imaging techniques. Further investigation and advancement of multipiezo materials could yield breakthroughs, further augmenting their usefulness across various industries and scientific domains. Exploring ferroelectric ML materials offer new prospects for developing advanced materials with unique electro-mechano-optical properties.

Achieving Ultrasound-Excited Emission with Organic Mechanoluminescent Materials.

Unlike traditional photoluminescence (PL), mechanoluminescence (ML) achieved under mechanical excitation demonstrates unique characteristics such as high penetrability, spatial resolution, and signal-to-background ratio (SBR) for bioimaging applications. However, bioimaging with organic mechanoluminescent materials remains challenging because of the shallow penetration depth of ML with short emission wavelengths and the absence of a suitable mechanical force to generate ML in vivo. To resolve these issues, the present paper reports the achievement of ultrasound (US)-excited fluorescence and phosphorescence from purely organic luminogens for the first time with emission wavelengths extending to the red/NIR region, with the penetrability of the US-excited emission being considerably higher than that of PL. Consequently, US-excited subcutaneous phosphorescence imaging can be achieved using a mechanoluminescent-luminogen-based capsule device with a quantified intensity of 9.15 ± 1.32 × 104 p s-1 cm-2 sr-1 and an SBR of 24. Moreover, the US-excited emission can be adequately tuned using the packing modes of the conjugated skeletons, dipole orientation of mechanoluminescent luminogens, and strength and direction of intermolecular interactions. Overall, this study innovatively expands the kind of excitation sources and the emission wavelengths of organic mechanoluminescent materials, paving the way for practical biological applications based on US-excited emission.

Advanced Optical‐Thermal Integrated Flexible Tactile Sensor for High‐Fine Recognition of Liquid Property in Non‐Contact Mode

AbstractFlexible sensors have been applied to accurately identify the basic features of various solid objects. However, a significant obstacle is the accurate identification of liquids, due to it is impossible to exert force directly on those. Here, an optical‐thermal flexible tactile sensor is designed for liquid recognition, which integrates PEDOT:PSS/SrTiO3 thermoelectric foam and ZnS‐CaZnOS mechanoluminescent (ML) film coated with thermoplastic polyurethane (TPU), enabling the simultaneous detection of thermal and optical changes with low interference, via its exceptional mechanical stimuli‐caused light and superior thermoelectric voltage, respectively. In addition, the TPU coating imparts the device with excellent hydrophobic and oleophobic properties, enhancing its durability in complex conditions. This flexible sensor, possessing high stability under thermal and mechanical cycles, can distinguish different pure solvents and turbid suspensions, achieving a high‐fine recognition accuracy of 95% and 97.5%, respectively, with the aid of the fusion algorithm of multimodal sensory data based on the thermal and optical outputs. This capability of the device can underscore the practical utility of humanoid robots to identify hazardous liquids in some scenarios like safety inspection and kitchen condiments, which addresses the critical gaps in current sensory technologies by providing a robust, sensitive, and multifunctional strategy for accurate liquid recognition.

Effect of Polymer Encapsulation on the Mechanoluminescence of Mn2+-Doped CaZnOS.

Rare earth and transition metal ion-doped CaZnOS has garnered significant attention for its exceptional mechanoluminescence (ML) performance under mild mechanical stimuli and its capability for multicolor emissions. Since powdered phosphors are not directly usable, they require encapsulation within with polymers to create stable structures. This study investigates Mn2+-doped CaZnOS (CaZnOS:Mn2+) as the ML phosphor, optimizing its performance by varying the Mn2+ content, resulting in bright orange-red emissions from the d-d transitions of the Mn2+ activator. A quantum efficiency of 59.08% was achieved through the self-sensitization of the matrix lattice and energy transfer to the Mn2+ luminescent centers. The enhancement in ML due to Mn2+ doping is attributed to the reduced trap depth and increased trap concentration. Encapsulation with four polymers-PDMS, PU, SIL, and RTV-2-was explored to further optimize ML performance. Among these, PDMS provides the best ML output and sensitivity, owing to its slightly cross-linked structure and good triboelectric properties. The optimized CaZnOS:0.03Mn2+/PDMS composite, featuring excellent flexibility and recoverability, shows great potential for applications in anti-counterfeiting encryption, stress sensors, and wearable devices.

Scale-Bridging Mechanics Transfer Enables Ultrabright Mechanoluminescent Fiber Electronics.

Mechanoluminescent (ML) fibers and textiles enable stress visualization without auxiliary power, showing great potential in wearable electronics, machine vision, and human-computer interaction. However, traditional ML devices suffer from inefficient stress transfer in soft-rigid material systems, leading to low luminescence brightness and short cycle life. Here, we propose a tendon-inspired scale-bridging mechanics transfer mechanism for ML composites, which employs molecular-scale copolymerized cross-linking and nanoscale inorganic nanoparticles as hierarchical stress transfer sites. This strategy effectively reduces the dissipation of stress in molecular chain segments and alleviates local stress concentration, increases luminescence by 9 times, and extends cycle life to more than 10,000 times. Furthermore, a scalable (kilometer-scale) anti-Plateau-Rayleigh instability manufacturing technology is developed for thermoset ML fibers, compatible with various existing textile techniques. We also demonstrate its system-level applications in motion capture, underwater interaction, etc., providing a feasible strategy for the next generation of smart visual textiles.

Mechanoluminescence of ZnS: Cu@Al2O3 enabled optical fiber microlens passive tactile sensor for hardness recognition.

We propose an optical fiber microlens (OFM) passive tactile sensor (OFMPTS) for hardness recognition. The sensor features a core-shell structure, with an OFM as the core and an elastic mechanoluminescence (ML) matrix shell, which is composed of ZnS: Cu@Al2O3 doped with 10 nm SiO2 particles and polydimethylsiloxane (PDMS). Utilizing the Hertz model, the ML intensity of the sensor is correlated to the elastic modulus of the sample, which enables precise hardness detection. The microlens fiber structure significantly enhances photon collection efficiency, thereby allowing for effective coupling of the ML signal. In press mode, OFMPTS differentiates between five PDMS hardness levels. It can also operate in scan or tap mode, identifying hidden foreign bodies and tissue masses through response curve analysis. The sensor, which requires no external light source, expands the capabilities of optical hardness measurement.

High-Stability Near-Infrared Luminescent Glass Ceramic and Its Applications.

Near-infrared (NIR) light, valuable for its biological penetration and invisibility to the human eye, is a crucial tool in biomedicine, environmental monitoring, anticounterfeiting, and information encryption, yet traditional NIR luminescent materials are often unstable in humid conditions. Here, a highly stable MgGeO3:Mn2+ glass ceramic (GC) with NIR luminescence was successfully synthesized. As-obtained GC700 boasts exceptional luminescent capabilities and possesses abundant trap structures, enabling data inscription with a 405 nm laser and retrieval via laser/thermal excitation. Moreover, the emission peak of Mn2+ can be manipulated from 630 to 691 nm by increasing the annealing treatment temperature. With the harnessing of the effective NIR emission, stable carrier characteristics, and numerous trap structures, there is potential for application in information encryption. Accordingly, we explored the application of MgGeO3:Mn2+ GC (GC700 and GC800) samples in precious three-dimensional (3D) information storage and NIR mechanoluminescence (ML) for biological tissue imaging. These applications demonstrate the potential and versatility of electron-capturing NIR luminescent materials in a range of cutting-edge fields.

Near-Infrared Mechanoluminescence from Cr3+-Doped Spinel Nanoparticles for Potential Oral Diseases Detection.

Mechanoluminescence (ML) phosphors have found various promising utilizations such as in non-destructive stress sensing, anti-counterfeiting, and bio stress imaging. However, the reported NIR MLs have predominantly been limited to bulky particle size and weak ML intensity, hindering the further practical applications. For this regard, a nano-sized ZnGa2O4: Cr3+ NIR ML phosphor is synthesized by hydrothermal method. By improving the synthesis method and regulating the chemical composition, the NIR ML (600-1000nm) intensity of such nano-materials has been further enhanced about four times. The reasons for the ML performance difference between micro-/nano- sized phosphors also have been preliminarily analyzed. Additionally, this work probes into the ML mechanism deeply in traps' aspect from band structure and defect formation energy, which can supply significant references for a new approach to develop efficient NIR ML nanoparticles. Finally, due to excellent tissue penetration capability, nano-sized ZnGa2O4:Cr3+ NIR ML phosphor shows great potential applications in biomedical fields such as for the detection of clinical oral diseases.

Smart mechanoluminescent phosphors: A review of zinc sulfide‐based materials for advanced mechano‐optical applications

AbstractThe quest for mechanoluminescence (ML) in zinc sulfide (ZnS) spans more than a century, initially sparked by observations of natural minerals. There has been a resurgence in research into ML materials in recent decades, driven by advances in optoelectronic technologies and a deeper understanding of their luminescent properties under mechanical stress. ZnS, in particular, has garnered attention owing to its remarkable ability to sustain luminescence after more than 100,000 mechanical stimulations, positioning it as a standout candidate for optoelectronic applications. In contrast to conventional photoluminescent and electroluminescent light sources, ZnS composite elastomers have emerged as flexible, stretchable self‐powered light sources with considerable practical implications. This review introduces the development history, ML mechanisms, prototype ML devices, ZnS‐based ML material preparation methods, and their diverse applications spanning environmental mechanical‐to‐optical energy conversion, E‐signatures, anti‐counterfeiting, wearable information sensing devices, advanced battery‐free displays, biomedical imaging, and optical fiber sensors for human–computer interactions, among others. By integrating insights from ML‐optics, mechanics, and flexible optoelectronics, and by summarizing pertinent perspectives on current scientific challenges, application technology hurdles, and potential solutions for emerging scientific frontiers, this review aims to furnish fundamental guidance and conceptual frameworks for the design, advancement, and cutting‐edge application of novel mechanoluminescent materials.

Intense and sensitive green mechanoluminescence by Tb3+ doping in Y3GaO6

In this study, an efficient mechanoluminescent material, namely Y3GaO6:Tb3+, with green emission was prepared by high-temperature solid-phase synthesis. X-ray diffraction (XRD) shows that the samples belong to the orthorhombic crystal system with the space group Cmc21. The luminescence intensity of the materials is related to the content of the luminescent centers, and both photoluminescence (PL) and mechanoluminescence (ML) show that the optimum doping level of Tb3+ is 0.07. In both tensile and frictional applications, the ML intensity is linearly correlated with the magnitude of applied stress. Analysis of the thermoluminescence (TL) spectra indicates that the ML of the material arises from carriers released from the trap under stress stimulation, thus revealing its mechanism of ML property. Finally, the study demonstrates the mechanoluminescence pattern of Y3GaO6:Tb3+.

Achieving Tunable Mechanoluminescence in CaZnOS:Tb3+, Sm3+ for Multicolor Stress Sensing.

Mechanoluminescent (ML) materials can exhibit visible-to-near-infrared mechanoluminescence when responding to the fracture or deformation of a solid under mechanical stimulation. Transforming mechanical energy into light demonstrates promising applications in terms of visual mechanical sensing. In this work, we synthesized the phosphor CaZnOS:Tb3+, Sm3+, which exhibited intense and tunable multicolor mechanoluminescence without pre-irradiation. Intense green ML materials were obtained by doping Tb3+ with different concentrations. Tunable multicolor mechanoluminescence (such as green, yellow-green, and orange-red) could be realized by combining green emission (about 542 nm), attributed to Tb3+, and red emission (about 600 nm) generated from the Sm3+ in the CaZnOS substrate. The tunable multicolor ML materials CaZnOS:Tb3+, Sm3+ exhibited intense luminance and recoverable mechanoluminescence when responding to mechanical stimulation. Benefiting from the excellent ML performance and multicolor tunability in CaZnOS:Tb3+, Sm3+, we mixed the phosphor with PDMS and a curing agent to explore its practical application. An application for visual mechanical sensing was designed for handwriting identification. By taking a time-lapsed shot while writing, we easily obtained images of the writer's handwriting. The images of the ML intensity were acquired by using specific software to transform the shooting data. We could easily distinguish people's handwriting through analyzing the different ML performances.