RESUMO
We demonstrate a hybrid nanocomposite combining mesoporous silica, p SiO 2 , as a host medium and guest lithium niobate LiNbO 3 nanocrystals embedded into tubular silica nanochannels by calcination of the precursor mixed solution of lithium and niobium salts. High-resolution transmission electron microscopy, X-ray diffraction and Raman scattering techniques reveal trigonal LiNbO 3 nanocrystals within the p SiO 2 nanochannels, indicating their random texture morphology. Annealing at high temperatures ( 950 ∘ C) during calcination also leads to partial crystallization of the p SiO 2 matrix with the formation of trigonal α - SiO 2 nanocrystals. The Raman microscopy analysis of the p SiO 2 : LiNbO 3 nanocomposite reveals three structural crystalline phases, α - SiO 2 , LiNbO 3 and a mixed phase which involves the α - SiO 2 phase of host membrane and LiNbO 3 nanocrystals embedded into the membrane. The finite size of the LiNbO 3 nanocrystals results in specific features of the LO-TO phonon frequency splitting, which are investigated by Raman microscopy. In the transmission geometry, the second harmonic generation emission exhibits no Maker fringes and is characterized by a broad angular diagram of diffusely scattered light. The second harmonic generation response is independent of the polarization direction of the incident pump light, thus indicating a spatial isotropy of the nonlinear optical conversion in the p SiO 2 : LiNbO 3 composite, consistent with the randomly oriented textural morphology of the deposited LiNbO 3 nanocrystals. The contribution of the guest LiNbO 3 nanocrystals to the second harmonic generation effect was found to be strongly dominant compared to the partially crystallized host p SiO 2 matrix. The nanocomposite p SiO 2 : LiNbO 3 membrane, set in the 90 ∘ nonlinear optical geometry, shows unusually high diffusely transmitted second harmonic generation light (back-reflected emission), apparently supported by internal light reflection from the tubular nanochannel network. Despite the fundamental interest, the revealed anomalous back-reflected second harmonic generation emission from p SiO 2 : LiNbO 3 nanocomposite membranes expands the prospects for their photonic and nonlinear optical applications.
RESUMO
High-quality CsCu2X3 and Cs3Cu2X5 (X = Cl, Br, I) nanocrystals (NCs) exhibit excellent optoelectronic, physical, and chemical properties for detection of UV radiation due to large carrier mobility and lifetime, and heavy atoms. The nanocrystal materials can be prepared via a low-cost and simple solid-state synthesis. However, poor reproducibility and complex synthesis methods of obtaining perovskite NC thin films represent a drawback for the fabrication of the commercial photoelectric device. To address these issues, we develop highly stable CsCu2X3 and Cs3Cu2X5 NC materials using a facile solid-state reaction method for the scale-up production of halogen lead-free perovskites. We suggest a distinctive way to design a series of nanocrystalline perovskites using short-term synthesis and study the mechanism of perovskite formation using thermal solid-state synthesis. These all-inorganic and lead-free CsCu2X3 and Cs3Cu2X5 exhibit large photoluminescence quantum yields (PLQYs) up to 95.2%. Moreover, flexible paper photodetectors based on this series of lead-free perovskites show strong photoselectivity and bending stability at 254 nm, 365 nm, and 405 nm wavelengths. High-quality responses with a responsivity of 1.1 × 10-3 A W-1 and detectivity of 2.71 × 109 jones under UV illumination (10 µW cm-2) at a bias voltage of 5 mV are demonstrated. These results open prospects for designing photodetectors, LEDs, and other photosensitive devices.