A distinctive signature in the Raman and photoluminescence spectra of intercalated PbI2

Through correlated studies using scanning electron microscopy (SEM), Raman spectroscopy and low-temperature photoluminescence (PL) we have demonstrated that the intercalated PbI 2 with ammonia, poly (vinyl alcohol) and polyacrylamide are characterized by a distinctive signature in the Raman and photoluminescence spectra. After intercalation, the Raman spectrum of PbI 2 reveals an orthorhombic structure, identical with that observed on the micrometric scale, of KPbI 3 rod-like particles resulting from the reaction between Pb(NO 3 ) 2 and KI, carried out in liquid media such as ethanol and acetonitrile. The rods and the intercalated PbI 2 are characterized by a new and strong emission band at 2.23 eV (about 550 nm) that appears at 77 K under an excitation wavelength of about 340 nm. Modification of the Raman and PL spectra results from a compressing effect produced by the penetration between the PbI 2 layers of different molecular species. The compression acting primarily on the iodine layers has the result of lowering the contribution of the 5p states of I − ions to the constitution of the electronic level situated at the top of valence band of PbI 2 , so that the photoluminescence of intercalated PbI 2 acquires the characteristics of Pb 2+ emission when it is dissolved in an alkali halide crystal.