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Metal halide perovskite semiconductors are widely used in solar cells, light-emitting diodes, photodetectors, micro nano lasers and other research fields in recent years because of their excellent characteristics such as morphological diversity, high photoluminescence quantum yield and tunable light-emitting wavelength (covering the whole visible light band).
Candidate recommendation for "2020 top 10 optical developments in China"
Using perovskite film, single crystal micro meter wire, micro disk, nano crystal and other perovskite materials as gain medium, researchers have developed a variety of micro nano lasers. At present, the perovskite micro nano laser can achieve low threshold and high quality laser output through the design of matched optical cavity size and structure. However, as a typical ionic crystal, perovskite materials are easy to decompose in water, and humid air can destroy the structural stability of perovskite materials, thus seriously weakening the photoelectric properties of perovskite materials.
In order to solve the problem of stability of perovskite materials, the research team of Lei dangyuan, associate professor of City University of Hong Kong, developed a method to synthesize perovskite nanoparticles with good water resistance by "Pb-S" coordination bonding. In this method, the perovskite QDs with a diameter of about 170 nm are sealed in silica particles, which makes the perovskite QDs emit fluorescence continuously and stably in water for more than 6 weeks.
In addition, the team injected the perovskite @ silica nanoparticles, which are much smaller than the near-infrared wavelength, into the optical microcavity as the gain medium, and realized the low threshold perovskite up conversion laser pumped by near-infrared and working in water for the first time.
The research team selected the coupling agent (3-Mercaptopropyltrimethoxysilane) which can form stable "Pb-S" coordination bond with "Pb" ion in perovskite to package the perovskite quantum dots. Due to the coordination bonding of "Pb-S", the silane molecules first tightly bond with the surface of perovskite quantum dots, and then dehydrate and condense the silane molecules to form a dense silica shell to tightly and evenly cover the perovskite quantum dots, thus preparing perovskite @ silica nanoparticles with strong water resistance and uniform size.
The perovskite quantum dots sealed in silica not only have no change in structure, but also have high photoluminescence quantum yield and large nonlinear absorption cross section. Figure 1 shows the synthesis and characterization results of waterproof perovskite @ silica nanoparticles.
Fig. 1 synthesis and characterization of waterproof perovskite @ silica nanoparticles. (a) Schematic diagram of synthesis principle and steps; (b) csppbbr3 SEM micrographs of perovskite quantum dots; (c) SEM and TEM micrographs of perovskite @ silica nanoparticles; (f) HRTEM micrographs of perovskite quantum dots encapsulated in silica; (g) SEM and element distribution images of perovskite @ silica nanoparticles; (H) UV light Photo of perovskite @ silica nanoparticles dispersed in water.
Because the perovskite @ silica nanoparticles synthesized by this method are uniform in size and much smaller than the near-infrared wavelength, they can be used as gain medium combined with optical microcavity to build micro nano laser, as shown in Figure 2.
Fig. 2 water resistant laser based on perovskite @ silica nanoparticles. (a) Schematic diagram of optical path for two-photon pump laser test; (b) quantum yield of photoluminescence of two-photon pump Echo Wall mode laser with immersion time based on perovskite @ silica nanoparticles and perovskite quantum dots respectively, illustrated with optical photos of laser immersed in water for different times under the irradiation of ultraviolet lamp; (c) absorption and emission of two-photon (d) the emission spectrum of perovskite @ silica nanoparticle laser with 800 nm femtosecond laser pumped energy density after 13 hours of immersion in water; (E) the relationship between the integral intensity of the emission spectrum and the full width of the half peak and the pump energy density.
The research team further demonstrated that the echo wall mode laser prepared by the nanoparticles with good water resistance and excellent optical performance can still work under low threshold two-photon excitation after being immersed in water for 13 hours. This study will not only accelerate the industrialization of perovskite quantum dot lasers, but also expand the research of perovskite materials in the fields of biological imaging, fluorescent labeling and so on.
Relevant research results were published on nature communications [11:1192 (2020)] under the title of "water resident perovskite nanodots enable robot two photon lasing in acoustic environment".
The corresponding author of this paper is associate professor Lei Dangyi of City University of Hong Kong, and the first author is Li Siqi, a doctoral student. The partners include Professor Ren Guangyu, vice president of University of Hong Kong, Professor Andrey rogach, director of functional Photonics Research Center, Professor Manish chhowalla, Goldsmiths' Professor of materials science, Cambridge University, and Assistant Professor Zhu ye, Hong Kong University of technology.
Paper link:
https://www.nature.com/articles/s41467-020-15016-2
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