Molten Salt Shielded Synthesis of Monodisperse Layered CaZnOS‐Based Semiconductors for Piezophotonic and X‐Ray Detection Applications

Abstract

light-generators, stress sensing, flexible, and stretchable displays, mechanical energy harvesting and conversion, and integrated tribotronic devices. [1][2][3][4][5][6][7][8][9][10] They can emit light and are regarded as smart creatures (like Noctiluca scintillans shining by the impact of waves) when exposed to external momentary stimuli. [11][12][13][14] Many materials discovered in nature provide the capability to emit light in response to dynamic forces/pressures, whether natural or man-made, such as quartz and sugar. [15,16] There are two categories of ML materials systems: organics and inorganics; [17,18] however, most of the current organic ML materials emit photons by releasing energy from the breaking of chemical bonds, resulting in a poor recovery, or requiring recrystallization to reproduce the light emitting process. Inorganic ML materials can be divided into insulators and semiconductors. As one of the II-VI ML semiconductors, ZnS has very interesting mechanical-to-optical properties, owing to its labile changing elastic and plastic deformation crystal structure, as well as its special piezoelectric and friction characteristics. [19][20][21][22][23][24] The novel ML properties of ZnS-based composites have aroused broad research interest in recent years. [1,[26][27][28][29][30][31] Semiconductors such as doped ZnS, can directly convert mechanical energy into light energy, providing broad application prospects in the fields of stress/strain sensing, wind/droplet driving displays, CaZnOS-based semiconductors are the only series of material system discovered that can simultaneously realize a large number of dopant elements to directly fulfill the highly efficient full-spectrum functionality from ultraviolet to near-infrared under the same force/pressure. Nevertheless, owing to the high agglomeration of the high temperature solid phase manufacturing process, which is unable to control the crystal morphology, the application progress is limited. Here, the authors report first that CaZnOS-based fine monodisperse semiconductor crystals with various doping ions are successfully synthesized by a molten salt shielded method in an air environment. This method does not require inert gas ventilation, and therefore can greatly reduce the synthesis cost and more importantly improve the fine control of the crystal morphology, along with the crystals' dispersibility and stability. These doped semiconductors can not only realize different colors of mechanical-to-optical energy conversion, but also can achieve multicolor luminescence under low-dose X-ray irradiation, moreover their intensities are comparable to the commercial NaI:Tl. They can pave the way to the new fields of advanced optoelectronic applications, such as piezophotonic systems, mechanical energy conversion and harvesting devices, intelligent sensors, and artificial skin as well as X-ray applications.

New Strategy: Molten Salt‐Assisted Synthesis to Enhance Lanthanide Upconversion Luminescence

“…The presence of liquid-phase molten salts between the generated powders prevents the particles from contacting and linking with each other. [41][42][43] What's more, most conventional syntheses with molten salts require washing away them at the end, which could have an impact on the surface properties of the products and adds to complication of the experiment. [44][45][46] In this case, NaCl evaporates away gradually at high temperatures after coming into play.…”

Environmentally Stable and Self-Recovery Flexible Composite Mechanical Sensor Based on Mechanoluminescence

“…ML refers to the phenomenon where materials emit light under mechanical stimulation (friction, stretching, compression, tearing, etc. ), − which is regarded as an effective way to realize mechanical distribution detection and imaging and has received extensive attention in earlier research work. − For example, in 2008, Li et al coated a SrAl 2 O 4 : Eu 2+ composite film on a hole-drilled aluminum plate, and the intensity of the ML of the SrAl 2 O 4 : Eu 2+ film during the application of tensile forces to the surface of the plate was recorded using a high-speed CCD camera; it was finally found that the finite element method stress distribution calculation was the same as the strength distribution detected by ML. In 2012, Terasaki et al recorded a SrAl 2 O 4 : Eu 2+ composite film embedded in the gap of a concrete bridge, and the local ML image in the process of vehicles passing through the bridge was recorded by a sensitive CCD camera.…”

Smart Mechanoluminescent Phosphors: A Review of Strontium‐Aluminate‐Based Materials, Properties, and Their Advanced Application Technologies

“…[95] The molten salt method is very convenient and low-cost and may be advantageous in terms of luminescent brightness. For some other oxidation-prone ML compounds [96][97][98][99] such as massprepared sulfides or sulfur oxides, the molten salt method allows some reactions that usually must be carried out in an inert gas to be carried out in air, with reduced costs and effective control over the morphology and size of the crystals.…”