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Mechanoluminescent (ML) materials can directly convert external mechanical stimulation into light without the need for excitation from other forms of energy, such as light or electricity. This alluring characteristic makes ML materials potentially applicable in a wide range of areas, including dynamic imaging of force, advanced displays, information code, storage, and anti-counterfeiting encryption. However, current reproducible ML materials are restricted to sulfide- and oxide-based materials. In addition, most of the reported ML materials require pre-irradiation with ultraviolet (UV) lamps or other light sources, which seriously hinders their practical applications. Here, we report a novel ML material, MgF 2 :Mn 2+ , which emits bright red light under an external dynamic force without the need for pre-charging with UV light. The luminescence properties were systematically studied, and the piezophotonic application was demonstrated. More interestingly, unlike the well-known zinc sulfide ML complexes reported previously, a highly transparent ML film was successfully fabricated by incorporating MgF 2 :Mn 2+ into polydimethylsiloxane (PDMS) matrices. This film is expected to find applications in advanced flexible optoelectronics such as integrated piezophotonics, artificial skin, athletic analytics in sports science, among others., Competing Interests: Conflict of interest The authors declare that they have no conflict of interest., (Copyright © 2021. Published by Elsevier B.V.)

Visible light‐based human–machine interactive media is capable of transmitting electrical readouts to machines and providing intuitive feedback to users simultaneously. Currently, many inorganic mechanoluminescent (ML) materials‐based interactive media, typically ZnS‐loaded phosphors (ZLPs), have been successfully demonstrated. However, organic ML materials‐based solutions were rarely exploited despite their huge merits of strong structural modification, abundant luminescence property, low cost, easy preparation, and so on. Here, we propose a novel interactive tactile display (ITD) based on organic ML materials (Cz‐A6‐dye) and triboelectric nanogenerator, with ultra‐brightness (130% enhancement) and ultra‐low threshold pressure (57% reduction) as compared to ZLPs. The proposed ITD achieves the conversion of weak mechanical stimuli into visible light and electrical signals simultaneously, without extra power supplies. Furthermore, the relationship between the luminous performance of organic ML materials and mechanical force is quantified, benefiting from the uniform ML layer prepared. Enabled by convolutional neural networks, the high‐accuracy recognition (97.1%) for handwriting and identity of users is realized at the same time. Thus, the ITD has great potential for intelligent wearable electronics and classified military applications. [ABSTRACT FROM AUTHOR]

Self‐recoverable mechanoluminescence (ML) is becoming a novel technology widely used in the fields of sensing, display, and artificial intelligence. The dominant ML material, ZnS: Mn2+, is reported to solely present a yellow emission color, which limits the applications of self‐recoverable ML materials to a large extent. Herein, an effective strategy to extend the ML emission range of ZnS: Mn2+ by the ferromagnetic coupling of Mn2+ ions are reported. Under the thermal carbon‐reduction atmosphere (TCRA), the emission ranges of ML, photoluminescence (PL), and persistent luminescence spectra of ZnS: Mn2+ phosphors are all successfully broadened from yellow to red. Furthermore, as for the PL and ML intensities of ZnS: Mn2+, they are intensified to 1.76 and 3.23 folds larger under the TCRA treatment than those in pure nitrogen, respectively. Various spectra and magnetic test results reveal that the red emission bands of ZnS: Mn2+ @TCRA phosphors originate from the ferromagnetic coupling of Mn2+ ions. This study is the first to realize strong red emission and tunable multicolor luminescence in the conventional ZnS‐based phosphors, which introduces opportunities for discovering the multiband emissions of Mn2+ ion in other compounds. Brightly multicolored ZnS: xMn2+ @TCRA elastic films have been fabricated to demonstrate their anti‐counterfeiting and security applications. [ABSTRACT FROM AUTHOR]

Mechanoluminescence, a smart luminescence phenomenon in which light energy is directly produced by a mechanical force, has recently received significant attention because of its important applications in fields such as visible strain sensing and structural health monitoring. Up to present, hundreds of inorganic and organic mechanoluminescent smart materials have been discovered and studied. Among them, strontium‐aluminate‐based materials are an important class of inorganic mechanoluminescent materials for fundamental research and practical applications attributed to their extremely low force/pressure threshold of mechanoluminescence, efficient photoluminescence, persistent afterglow, and a relatively low synthesis cost. This paper presents a systematic and comprehensive review of strontium‐aluminate‐based luminescent materials' mechanoluminescence phenomena, mechanisms, material synthesis techniques, and related applications. Besides of summarizing the early and the latest research on this material system, an outlook is provided on its environmental, energy issue and future applications in smart wearable devices, advanced energy‐saving lighting and displays. [ABSTRACT FROM AUTHOR]

Mechanoluminescence (ML), as an optical response to deformation stimuli, shows great potential in high‐end stress sensing, ultrasonic field visualization, and multidimensional anti‐counterfeiting. However, processive practical applications in bio‐medicine are constrained by the discovery of near‐infrared (NIR) ML materials. Unlike lanthanides (Ln3+) with sharp multiplets, two kinds of Cr3+‐doped NIR ML materials, gallate spinel (ZnGa2O4:Cr3+, Zn3Ga2GeO8:Cr3+) and gallate magnetoplumbite (SrGa12O19:Cr3+) are here reported. Owing to the intrinsic cation antisite defects and cation vacancies in the matrix, these materials exhibit bright NIR ML under a relatively low load (20 N). In particular for SrGa12O19:Cr3+ (750 nm, peak; 100 nm, FWHM) with low persistent luminescence (PersL) interference, the ML behavior can be further rejuvenated under UV and sunlight irradiation. SrGa12O19:Cr3+ also shows bright NIR emission under photo‐ and thermo‐stimulation. Owing to their excellent tissue penetration and concealment capability, NIR ML materials show great potential in the fields of bio‐medicine and anti‐counterfeiting. [ABSTRACT FROM AUTHOR]

Mechanoluminescence (ML) and long-afterglow (LAG) luminescence are usually studied independently and applied in different fields. SrAl2O4:Eu(II)/Dy(III) (SAOED) is a well-known long-afterglow and elastico-mechanoluminescent material that emits bright green visible light through absorption of photon energy, followed by naturally thermal release or excitation by force. The ML intensity is directly proportional to the magnitude of the applied dynamic force in the elastic range, making it uniquely applicable in a wide field of active visualization of stress/strain sensing. As a LAG material, SAOED is also a commercial photoluminescence (PL) phosphor owing to its high initial brightness and ultralong luminescence duration. Considering the ML and LAG properties and making better applications, the influence of dopants on both characteristics should be studied. In this study, we investigated the concentration effect of Eu (II) and Dy (III) co-doping on the PL, ML, and LAG properties of SAO. A maximum twofold ML brightness enhancement was achieved, and a suitable stress-induced afterglow and stress-free afterglow features were observed through Eu(II) and Dy(III) co-doping. Taking advantage of these properties, we demonstrate the application of Dy- and Eu-co-doped strontium aluminate in environmental–mechanical energy conversion. Owing to its mechanically excited luminescence properties, it can reduce electricity consumption and can also serve as an environmental motion warning in traffic signing, sports scene, and other related fields. The results enriched the application scenarios of SAOED composites as a multiluminescent smart material. We conduct a systematic analysis to investigate and confirm that the appropriate co-doping strategies to simultaneously obtain good mechanoluminescence and long-afterglow performance of strontium aluminate phosphors and their composites, demonstrate their applications in the environmental auxiliary lighting and sport-force indicator, which results can enrich the application scenarios of mechanoluminescent long-afterglow composites as a smart and energy-saving material. [ABSTRACT FROM AUTHOR]

Mechanoluminescence materials, which directly convert mechanical energy into light emission, have emerged as an emerging class of light-emitting materials with various applications. We designed various Mn-doped ternary heterojunctions CaZnOS-ZnS-SrZnOS were designed for the wearable clothes and printable things, which show battery-free light emitting, thereby providing a new idea for the development of wearable flexible self-luminous devices and for a wide range of applications in smart energy-saving display, safety and rescue, and anti-counterfeiting. [Display omitted] • The various Mn-doped ternary heterojunctions CaZnOS-ZnS-SrZnOS were designed, the ternary heterojunction materials have higher performance with ML intensity: over 60 times stronger than that of the SrZnOS. • The wearable clothes composed of mechanoluminscent Zippers and Velcro were designed to show battery-free light emitting, thereby providing a new idea for the development of wearable flexible self-luminous devices and for a wide range of applications in smart energy-saving display, safety and rescue, information security and human-robotic interface. • The printable things with force-driven light-emitting have be printed on the surface of various commodities or their packaging, which have opened the door of mechanoluminscent anti-counterfeiting applications. Mechanoluminescence (ML) materials, which directly convert mechanical energy into light emission, have emerged as an emerging class of light-emitting materials with various applications. Although significant progress has been made in the development of new ML materials and devices, their practical application is limited by their low intensity and homogenously structured host structures. Thus, multiple-structured host ML materials with high ML intensity and reproducibility are needed, particularly for wearable and printable ML light sources with high brightness. In this study, various Mn-doped ternary heterojunction ML materials, CaZnOS-ZnS-SrZnOS, are synthesised by high-temperature solid-phase reactions, and their luminescence properties are systematically tested. The result indicates that the ternary heterojunction materials have a higher ML intensity over 60 times stronger than the state-of-art SrZnOS: Mn2+, which is currently the brightest sample we have obtained. ML linearly depends on the magnitude of the applied force. Based on the synthesised ternary ML heterojunctions, repetitive self-driving luminescence of the zipper is achieved for the first time through powder modification and inlay; the clothes composed of our prepared zippers are pulled and bent when worn on the body to emit bright visible light. Additionally, a Velcro that can achieve light emission is developed; it provides a new idea for the development of wearable flexible self-luminous devices in the future. Simultaneously, movement-driven stress luminous printable objects that can be printed on the surface of various commodities or their packaging are demonstrated. The preparation of self-driven, battery-free, and electrode-free stress luminescence wearable low light sources has an important application trend, which can avoid the interference of the circuit and improve the stability of the devices, thus promising a wide range of applications in smart wear, energy-saving displays, safety and rescue, robotic skin, and information security. [ABSTRACT FROM AUTHOR]