Synchrotron X-ray powder diffraction under high pressures up to 33†MPa for mechanoresponsive materials.

Equipment for synchrotron X-ray diffraction at high pressures up to 33 MPa with an accuracy of ±0.1 MPa using a liquid as a pressure-transmitting medium has been developed. This equipment enables atomic-scale observation of the structural change of mechanoresponsive materials under applied pressures. The validity of the equipment is demonstrated by observation of the pressure dependence of the lattice parameters of copper. The observed bulk modulus of copper was found to be 139 (13) GPa which is a good agreement with the literature value. The developed equipment was subsequently applied to a repeatable mechanoluminescence material, Li0.12Na0.88NbO3:Pr3+. The bulk modulus and compressibility along the a and c axes were determined as 79 (9) GPa, 0.0048 (6) GPa-1 and 0.0030 (9) GPa-1, respectively, for the R3c phase. The advance of high-pressure X-ray diffraction will play an important role in understanding mechanoresponsive materials towards their atomic-scale design.

Flexible Mechanoluminescent SrAl2O4:Eu Film with Tracking Performance of CFRP Fracture Phenomena.

Non-destructive testing of carbon-fiber-reinforced plastic (CFRP) laminates with bidirectional fiber bundles (twill-weave) using a mechanoluminescence (ML) technique was proposed. The dynamic strain distributions and fracture phenomena of the CFRP laminates in the tensile testing were evaluated by the fabricated ML sensor consisting of SrAl2O4:Eu (SAOE) powder and epoxy resin. The ML images for the ML sensor attached to the CFRP laminates with bidirectional fiber bundles gave a net-like ML intensity distribution similar to the original twill weave pattern. Specifically, it was found that the ML intensity on the longitudinal fiber bundle, which is the same as the tensile direction, is higher than that on the transverse fiber bundle. This indicates that the ML sensor can visualize the load share between fiber bundles in different directions of the CFRP laminate with high spatial resolution. Meanwhile, the ML sensor could also visualize the ultrafast discontinuous fracture process of the CFRP laminates and its stress distribution. The amount of SAOE powder in the ML sensor affects the tracking performance of the crack propagation. A higher SAOE amount leads to a fracture of the ML sensor itself, and a lower SAOE amount leads to poor ML characteristics.

Effective Repeatable Mechanoluminescence in Heterostructured Li1- x Nax NbO3 : Pr3.

Mechanoluminescence (ML) is a striking optical phenomenon that is achieved through mechanical to optical energy conversion. Here, a series of Li1 -x Nax NbO3 : Pr3+ (x = 0, 0.2, 0.5, 0.8, 1.0) ML materials have been developed. In particular, due to the formation of heterostructure, the synthesized Li0.5 Na0.5 NbO3 : Pr3+ effectively couples the trap structures and piezoelectric property to realize the highly repeatable ML performance without traditional preirradiation process. Furthermore, the ML performances measured under sunlight irradiation and preheating confirm that the ML properties of Li0.5 Na0.5 NbO3 : Pr3+ can be ascribed to the dual modes of luminescence mechanism, including both trap-controllable and self-recoverable modes. In addition, DFT calculations further confirm that the doping of Na+ ions in LiNbO3 leads to electronic modulations by the formation of the heterostructures, which optimizes the trap distributions and concentrations. These modulations improve the electron transfer efficiency to promote ML performances. This work has supplied significant references for future design and synthesis of efficient ML materials for broad applications.

Elastico-mechanoluminescence in CaZr(PO4)2:Eu2+ with multiple trap levels.

We report on a novel elastico-mechanoluminescence (EML) phosphor of CaZr(PO4)2:Eu2+ for simultaneous luminescent sensing and imaging to mechanical load by the light-emitting of Eu2+ ions. The EML properties of CaZr(PO4)2:Eu2+ show an intense luminance (above 15 mcd m(-2)), a low load threshold (below 5 N), a broad measurement range for the dynamic load (up to 2000 N), and an accurate linear relationship of EML intensity against the applied load. The excellent EML characteristics are considered to originate from the piezoelectric crystal structure and the multiple trap levels with appropriate depths. An EML mechanism based on the electrons as the main charge carriers is proposed.

An intense elastico-mechanoluminescence material CaZnOS:Mn2+ for sensing and imaging multiple mechanical stresses.

The elastico-mechanoluminescence (EML) properties of CaZnOS:Mn2+ are investigated. The CaZnOS:Mn2+/epoxy resin composite can simultaneously "feel" (sense) and "see" (image) various types of mechanical stress over a wide energy and frequency range (ultrasonic vibration, impact, friction and compression) as an intense red emission (610 nm) from Mn2+ ions. Further, the accurate linear relation between emission intensity and different stress parameters (intensity, energy and deformation rate) are confirmed. The EML mechanism is explained using a piezoelectrically induced trapped carrier excitation mode. All the results imply that CaZnOS:Mn2+ has potential as a stress probe to sense and image multiple mechanical stresses and decipher the stress intensity distribution.

Ferroelectric Sr3 Sn2 O7 :Nd3+ : A New Multipiezo Material with Ultrasensitive and Sustainable Near-Infrared Piezoluminescence.

Ultrasensitive and sustainable near-infrared (NIR)-emitting piezoluminescence is observed from noncentrosymmetric and ferroelectric-phase Sr3 Sn2 O7 doped with rare earth Nd3+ ions. Sr3 Sn2 O7 :Nd3+ (SSN) with polar A21 am structure is demonstrated to emit piezoluminescence of wavelength of 800-1500 nm at microstrain levels, which is enhanced by the ferroelectrically polarized charges in the multipiezo material. These discoveries provide new research opportunities to study luminescence properties of multipiezo and piezo-photonic materials, and to explore their potential as novel ultrasensitive probes for deep-imaging of stress distributions in diverse materials and structures including artificial bone and other implanted structures (in vivo, in situ, etc).

LiNbO3 :Pr3+ : A Multipiezo Material with Simultaneous Piezoelectricity and Sensitive Piezoluminescence.

Red-emitting piezoluminescence (elasticoluminescence) is achieved by doping rare earth Pr3+ into the well-known piezoelectric matrix, LiNbO3 . By precisely tuning the Li/Nb ratio in nonstoichiometric Li x NbO3 :Pr3+ , a material that exhibits an unusually high piezoluminescence intensity, which far exceeds that of any well-known piezoelectric material, is produced. Li x NbO3 :Pr3+ shows excellent strain sensitivity at the lowest strain level, with no threshold for stress sensing. These multipiezo properties of sensitive piezoluminescence in a piezoelectric matrix are ideal for microstress sensing, damage diagnosis, electro-mechano-optical energy conversion, and multifunctional control in optoelectronics.

Electrostrictive and photoluminescent properties in Pr-doped (Ba,Sr)(Ti,Al)O3 ceramics.

Pr3(+)-doped (Ba,Sr)(Ti,Al)O3 ceramics were prepared using a conventional solid-state reaction technique. Multiple functions of electrostriction and photoluminescence were realized in the ceramics. Red emission (614 nm) was observed in the samples, and the intensity reached its largest value in the sample of 40 mol% Sr addition. Although the electrostrictive strain decreased in the Pr and Al doped samples, the temperature dependence is remarkably improved comparable to the undoped sample.

Large electrostrain and high optical temperature sensitivity in BaTiO3-(Na0.5Ho0.5)TiO3 multifunctional ferroelectric ceramics.

Ferroelectric (1 -x)BaTiO3-x(Na0.5Ho0.5)TiO3 ceramics with ferroelectric and up-conversion luminescent multifunctions were designed and fabricated by a solid state reaction process. Their structure, ferroelectric, piezoelectric, up-conversion photoluminescence and relative optical temperature sensing properties were investigated systematically. Crystal structure analysis and Rietveld refinements based on the powder X-ray diffraction data show that the ceramics crystallized in the tetragonal perovskite space group P4mm at room temperature. Enhanced electrical properties and strong green up-conversion luminescence with thermally coupled green emission bands centered at 523 and 553 nm were observed. For a typical sample x equals 0.05, a large electrostrain of 0.279% was obtained under a 70 kV cm(-1) electric field that is comparable to that of the PZT4. Meanwhile, the excellent optical temperature sensitivity (0.0063 K(-1) at 480 K) is higher than that of Er-doped BaTiO3 nanocrystal materials. The results suggest that the BaTiO3-(Na0.5Ho0.5)TiO3 material should be an attractive material for piezoelectric actuator and temperature sensing device applications.

Performance of single mechanoluminescent particle as ubiquitous light source.

In this study, we have investigated mechanoluminescent (ML) performance of single ML particle as ubiquitous light source. When using high-speed CCD camera with image intensifier and microscopic equipment, mechanoluminescence from single particle was observed. As to the quantitative ML evaluation of the single ML particle was carried out using photomultiplier, and successfully estimated the performance of the single ML particle as an intensity controllable light source in nW order.

Mechanoluminescent light source for a fluorescent probe molecule.

We have demonstrated an innovative ability of mechanoluminescent (ML) material as a light source for the first time. By appropriate smart size control and nondestructive mechanical stimulation, the ML particle can be considered a promising candidate of in situ light source for bio-imaging and photo-therapy even in a human body.

Direct visualization of ultrasonic power distribution using mechanoluminescent film.

In this research, a technique for measuring ultrasonic power with a mechanoluminescent (ML) sensing film was developed. A linear relationship was observed between the ultrasonic power and the ML intensity induced by ultrasonic vibration, indicating that ultrasonic power can be evaluated by measuring ML intensity. In addition, the ultrasonic power distribution on the surface of a transducer was visualized by recording ML images with a charge-coupled device camera.

Observation of mechanically induced luminescence from microparticles.

We have invented a new device based on atomic force microscopy that measures the emission from a single microparticle by force direct application using the AFM probe, and successfully observed emission in the region of the elastic deformation, friction, and destructive deformation.