Nanocrystalline/microcrystalline materials based on lead-halide units

The preparation, photoluminescence (PL) spectra and related properties of particulate (nanocrystalline/microcrystalline) materials based on Pb(BrxCl1-x)(3), Pb(BrxI1-x)(3), and Pb(ClxI1-x)(3) (x = 0-1) units, in several macroscopic forms, are reported. The materials in the form of suspensions in toluene or in toluene containing polymethyl methacrylate (PMMA) were obtained from the corresponding n-layer materials (or their precursors), mainly, by a titration-like method. This is the injection of solutions of the corresponding compounds with the Pb-n(BrxCl1-x)(3n+1), Pb-n(BrxI1-x)(3n+1), and Pb-n(ClxI1-x)(3n+1) (n > 2) units, respectively, into neat toluene or toluene-PMMA, with parallel observation of the PL-spectra. With this method, the mass of the lead-halide materials is controlled and the position of the low frequency PL band could be tuned in a wide spectral range, i.e., from ca. 400 to ca. 700 nm. From the suspensions in toluene the corresponding materials in the form of precipitates (powders) were obtained by centrifugation and decantation. From suspensions in toluene-PMMA, the corresponding materials in the form of composite thin films (of PMMA-matrix) were obtained by drop-casting, deep-coating and/or spin-coating techniques. So, blue, green, yellow and red narrow PL-band (of 20-35 nm) emitters (in forms of suspensions, powders and films) were obtained and their PL and optical absorption spectra were investigated further. The PL-intensity varies as in the case of CsPbBr3 particles in a CsBr matrix. Also, some similarities with the spectra of metal chalcogenide quantum dots were found. They were suggested as candidate materials for several optical and optoelectronic applications.