Sr₃Sn₂O₇:Sm³⁺ is a widely studied mechanoluminescent material, but there is still a lack of research on the doping amount of Sm³⁺. In this paper, Sr_3-xSn₂O₇: xSm³⁺ was prepared by a high-temperature solid-state method. A sample of Sr₃Sn₂O₇ with a small amount of Sm³⁺ still maintains a non-centrosymmetric double perovskite structure. The sample prepared has a stable photoluminescence, a long afterglow and mechanoluminescence after UV excitation or load application. The mechanoluminescence originates from the electron transition from the ⁴G_5/2 excited state of Sm³⁺ to the ⁶H_J (J=5/2, 7/2, 9/2) ground state. The luminescence performance was optimized by adjusting the value of x, and the optimum performance was achieved when x = 0.020. This study can provide a guidance for the future related research.

Sulfur element doped RbNa₃(Li₁₂Si₄O_16-yS_y):Eu²⁺ narrow-band blue emitting UCr₄C₄ phosphors were synthesized by a conventional high-temperature solid-state method. The zero-thermal-quenching performance for the UCr₄C₄ structure was obtained, i.e., the integrated emission intensity at 250 ℃ increases to 107% rather than that at room temperature. The sites occupation of Eu²⁺ ions and defect analysis reveal the corresponding luminescence adjustment and zero-thermal-quenching mechanism. Also, the cationic substitution strategy of Ti⁴⁺ for Si⁴⁺ is designed to eliminate the shoulder band peak located at 525 nm for RbNa₃(Li₁₂Si₄O_16-yS_y):Eu²⁺ phosphors, and the color purity of blue emission is improved from 61.1% to 83.7%. It is indicated that the as-prepared RbNa₃(Li₁₂Si₃TiO_16-yS_y):Eu²⁺ phosphors could be used as a blue-emitting candidate material for liquid crystal display backlighting. This work can provide a guidance for the design of UCr₄C₄ phosphors to achieve the zero-thermal-quenching performance and high color purity.

Mn²⁺ doped garnet-type Na₂CaSn₂Ge₃O₁₂ phosphor was selected and studied due to its abundant chemical compositions and several crystallographic sites. Several ion substitution strategies including the chemical substitution of Na⁺/Sr²⁺/Ba²⁺ on Ca²⁺ sites and the anti-site occupation of Sn⁴⁺/Ge⁴⁺ were designed for regulating the different energy traps and promoting multimode luminescence properties like persistent luminescence, X-ray storage capacities and mechano-luminescence. In addition, the X-ray luminescence storage and mechano-luminescence properties of these materials as well as their applications on X-ray luminescence extension imaging and stress sensing were also investigated.

Ti(C,N)-WC-Al₂O₃/Ti(C,N)-WC laminated ceramic materials with different layers and layer thickness ratios were prepared via microwave sintering. The variation of residual stress with layer number and layer thickness ratio was revealed by a finite element method, and the effects of layer number and layer thickness ratio on the macro-mechanical properties and micro-structural characteristics of the material were investigated. The results show that compared with the homogeneous material, the fracture toughness of the laminated material increases to 11.42 MPa·m^1/2, which is 2.5 times greater than that of the homogeneous material, indicating a superior toughening effect. The main reason is a combined effect of macroscopic residual compressive stress and massive microscopic crack deflections. The fracture mode of the laminated material is an effective mixed fracture mode. In such a mode, the transgranular fracture of the surface layer and the intergranular fracture of the matrix layer alternate, which is conducive to the increase of fracture toughness and to the improvement of the overall strength of the material.

The mechanism of mechanoluminescent(ML) materials is a highly interdisciplinary research field involving the composite processes of mechanics, electricity, magnetism, and optics. At present, some special phenomena that cannot be fully covered by the existing mechanism models indicate that the process mechanism of ML is not fully clarified. This review represented the process mechanism of ML and the existing mechanism models and development strategies. In addition, some challenges and research directions of ML materials were also described.

High quality ceramic targets is crucial to produce BaBiO₃-based negative temperature coefficient (NTC) thermosensitive films via RF magnetron sputtering. In this paper, the shrinkage, flatness and volume density of pure BaBiO₃ target were measured, and the orthogonal experiment was designed via changing the major factors (i.e., compressive time, sintering temperature, holding time and heating rate), and the structure-activity relationship between each factor and the target material quality index was analyzed. Also, based on the influence of sintering behaviors on the grain growth of BaBiO₃ ceramic targets, the key sintering process factors such as sintering temperature, holding time and heating rate were regulated by the phenomenological equation and intercept method to discuss the intrinsic relationship among the grain growth mechanism, growth index n and key influencing factors. According to the results by X-ray diffraction, Raman spectroscopy and scanning electron microscopy-enery dispersive spectroscopy, the phase structure and elemental composition of the target samples obtained at the given process factors were analyzed. The results show that BaBiO₃ ceramic targets with slight deformation, high density and good apparent quality can be obtained under the optimum conditions (i.e., compressive time of 12 min, sintering temperature of 750 ℃, holding time of 120 min and heating rate of 2 ℃/min).

A low-carbon Al₂O₃-C composite refractory was prepared with white fused alumina, flake graphite, active α-Al₂O₃ micron-sized powder, Al powder and Si powder as raw materials, and h-BN (in mass fraction 0%, and 3%) as additives. The effect of h-BN addition on the microstructure, physical properties and oxidation resistance of Al₂O₃-C refractories at different nitriding temperatures was investigated. The results show that the addition of h-BN promotes the formation of SiC whiskers. The cold compressive strength and cold modulus of rupture of the samples with h-BN addition after nitriding at 1 400 ℃ are 6% and 10% greater than those of the samples without h-BN addition, respectively. Also, the oxidation resistance of the samples with h-BN addition is significantly improved. Among those samples, the oxidation resistance of the samples with h-BN addition after nitriding at 1 500 ℃ is improved by 21%, compared with the samples without h-BN addition.

A novel afterglow mechanoluminescent (ML) composite elastic material was obtained with ZrO₂:Ti⁴⁺ phosphor synthesized by a solid-state method and PDMS polymer. The structure, luminescence and traps properties of the phosphor and the elastomer were investigated by X-ray diffraction, scanning electron microscopy, and spectroscopy. The results show that ZrO₂ belongs to a monoclinic system with a space group P21/c (No.14), which is a centrosymmetric structure, and its ML is irrelevant to the common piezoluminescence. The band gap of the matrix is 5.01 eV, and its width is large, which is conducive to the irradiation transition of the luminescence energy level. The cyan photoluminescence and afterglow luminescence with Ti⁴⁺ characteristic emission e_g→t_2g are obtained after Ti⁴⁺ is uniformly doped into ZrO₂ as a luminescence center. After it is irradiated by 254 nm ultraviolet lamp, the composite elastic material prepared with ZrO₂:Ti⁴⁺ phosphor and PDMS can emit bright cyan ML under the stimulation of external forces such as tearing, pressing, bending and stretching. The ML occurs clearly for several seconds. The afterglow mechanoluminescent phenomenon is linearly dependent on the stress and it can repeat after irradiation, indicating a promising application potential in the fields of stress visualization, force-light sensing, engineering detection and artificial skin. In addition, a possible mechanism of afterglow ML caused by triboelectricity induced trapped carrier excitation was also proposed.

The effect of cracking ages (i.e., 3, 7, 14 d and 28 d) on the self-healing of pure fly ash-based engineered geopolymer composite (FA-EGC) was evaluated by crack characteristics, tensile properties and water absorption. The components and microstructure of self-healing products of FA-EGC were investigated by Fourier transform infrared spectroscopy, X-ray diffraction and scanning electron microscopy with energy dispersive spectroscopy. The results show that there is an optimum self-healing effect of FA-EGC samples when cracking age is 7 d, a better recovery of ultimate tensile strength and a reduction in average water absorption rate can be obtained at the maximum decrease in crack width. The self-healing products of FA-EGC are the geopolymer gel generated by ongoing geopolymerization reaction and CaCO₃.

The bonding strength of epoxy grout-concrete composite was investigated by axial tensile test to reveal the bonding damage evolution mechanism between epoxy grout and concrete under dry and wet interface condition. The ringing count, b value and the spatial position of acoustic emission (AE) source during the tensile process of composite were obtained by AE technique, and the spatial evolution process of bonding damage of composite was analyzed. The evolution characteristics of strain and displacement damage on the fracture surface of the composite under wet and dry interface condition were obtained by a digital image correlation method. The results show that the bonding strength under dry interface condition is 60% higher than that under wet interface condition. Under wet interface condition, the AE source of epoxy grout-concrete is concentrated at the interface, and a regular strain concentration zone is formed at the interface, showing the characteristics of interface failure. Under dry interface condition, however, there are a lot of AE sources in the concrete, and there are several irregular strain concentration zones on the fracture surface, indicating the failure mode of the concrete matrix as a whole.