In a recent study published in the journal Materials Today Chemistry, researchers analyzed zinc (Zn)-doped cesium lead bromide (CsPbBr3-Cs4PbBr6) perovskite nanocrystals (NCs) core with silica-coated layered octyl-ammonium lead bromide [(OA)2PbBr4] perovskite shell via modified ligand assisted reprecipitation (LARP) synthesis method for biocompatibility and bioimaging applications.
Study: Impact of Zn-doping on the composition, stability, luminescence properties of silica coated all-inorganic cesium lead bromide nanocrystals and their biocompatibility. Image Credit: Leo Matyushkin/Shutterstock.com
Cesium lead halide (CsPbX3: X = I, Br, Cl) NCs have high emission intensity but very low structural stability against polar organic solvents, making them vulnerable and a source of cytotoxicity for living beings.
The newly developed shelled CsPbBr3-Cs4PbBr6 NCs exhibited an impressive green color emission with a 494-506 nm spectral range and a maximum photoluminescence quantum yield (PLQY) up to 88%.
CsPbX3 NCs for Optoelectronic Applications
CsPbX3 perovskite NCs have garnered immense attention in various optoelectronic applications due to their bright luminescence, high color purity, easy solution processability, high absorption coefficient, narrow emission full-width half maxima (FWHM), and easy dispersion in various liquid media.
However, their chemical and structural instability in organic polar solvents due to their strong ionic nature limits their biomedical applications.
As a solution, synthesis of core-shell nanostructure by coating these NCs with bulky organic ligands, silica, polymers, inorganic sulfide layer (ZnS, CdS, PbS, PbSe), high bandgap oxide layers (TiO2, ZnO, Al2O3), perovskite shell, and superhydrophobic framework structure can improve their stability. It can also reduce the non-radiative recombination processes and enhance the emission intensity by allowing efficient exciton recombination.
Additionally, the silica coat provides better moisture resistance, oxidation resistance, and increased specific surface area due to the formation of mesopores.
About the Study
In this study, researchers used the LARP synthesis method to synthesize Zn-doped CsPbBr3-Cs4PbBr6 NC core with a silica-coated layered (OA)2PbBr4 perovskite shell.
The Zn-doping controlled the composition ratio of CsPbBr3 to Cs4PbBr6 perovskite structures inside the core material and further improved the photoluminescence (PL) intensity and stability.
The team used (3-aminopropyl) trimethoxysilane [APTMS] for the silica source owing to their shorter chain length and less steric hindrance than (3-aminopropyl) triethoxysilane [APTES], which resulted in a faster reaction for the growth of silica coating around the perovskite NCs.
The composite samples with 0%, 20%, 40%, 60%, and 80% Zn-doping were denoted as NCs-0, NCs-20, NCs-40, NCs-60, and NCs-80, respectively.
X-ray diffraction (XRD) patterns revealed that NCs-0 had a mixture of two phases in its crystal structure: 0D rhombohedral Cs4PbBr6 phase and 3D monoclinic CsPbBr3. Also, further increase in the Zn-doping concentration in NCs-0 decreased the XRD peak intensities of rhombohedral Cs4PbBr6 crystal phase successively.
Moreover, the diffraction peaks shifted slightly to higher angles, which indicated a shrinkage in the perovskite crystal lattices due to the substitution of Zn-atoms at Pb-lattice places. However, the successive XRD peaks shifted to lower angles with excess Zn-doping in the NCs, owing to the introduction of interstitial Zn ions that caused lattice expansion.
Transmission electron microscopy (TEM) results showed a particle size distribution of NCs in the range of 5-40 nm with a mean particle size of 10.11 ± 5 nm.
The NCs exhibited an interplanar spacing of 0.66 nm corresponding to (001) lattice planes for the monoclinic CsPbBr3 phase.
Also, for NCs-40, Zn-doping slightly increased the particle size and size distribution uniformity, which was favorable for various optoelectronic applications.
The Fourier transform infrared spectroscopy (FTIR) spectrum revealed that all samples had strong absorption peaks located at 1099 and 756 cm-1, corresponding to the antisymmetric stretching vibration peak of Si-O-Si bonds and symmetrical stretching vibration peaks of Si-O bonds, respectively.
Thus, proving the presence of a strong silica coating. Moreover, the peak intensities of NCs-40 samples shifted to lower energies, evidencing improvement in peak intensities and enhanced binding of (OA)2PbBr4 layer to the core NCs with Zn-doping.
In summary, the researchers of this study synthesized Zn-doped CsPbBr3-Cs4PbBr6 perovskite NCs core with silica-coated layered (OA)2PbBr4 perovskite shell via modified LARP synthesis method and investigated its chemical and structural stability in a polar solvent, biocompatibility, and emission intensity in mammalian and plant cells.
The nanocrystals demonstrated a tunable high-intensity green color emission and an excellent PLQY of up to 88%. Hence, Zn-doped CsPbBr3-Cs4PbBr6 (core)-(OA)2PbBr4 (shell) is a promising composite material for bioimaging, biosensors, and agricultural applications.
Continue reading: Biomedical Applications of Perovskite Nanocrystals.
Kar, M., Chakraborty, R., Patel, U., Chakraborty, R., Ray, S., Acharya, T., Goswami, C., Bhaumik, S., (2022) Impact of Zn-doping on the composition, stability, luminescence properties of silica-coated all-inorganic cesium lead bromide nanocrystals and their biocompatibility, Materials Today Chemistry, 23, 100753. Available at: https://www.sciencedirect.com/science/article/pii/S2468519421003335?via%3Dihub