Metal Halides for Optoelectronic Applications

This Thesis focused on the improvement of the stability and the emission efficiency of different luminescent materials, in order to obtain promising compounds for optoelectronic devices. The main project was the synthesis of emissive hybrid metal halides as crystals, using different organic cations: methylammonium MA (CH6N+), butylammonium BA (C4H12N+), benzylammonium Bz (C7H10N+). In the first composition, expressed generally as MAxMnyBrz, two hybrid phases were synthesized varying the amount of NMF precursor, with yellow-green and red emissions, and also a temperature-dependent photoluminescence change. Using BA and Bz, the growing dimensions of the organic cations favored the formation of 2D layered crystal structures. In BA2(Pb,Mn)Br4, the precipitation of two different phases (pure-Pb and pure-Mn) was observed, with the typical blue emission of Pb2+ and the red one of Mn2+. Instead, in Bz2(Pb,Mn)Br4, all samples showed a red emission from Mn2+ (except for pure-Pb). Concerning other metal halide compounds, the synthesis of CsMnBr3 and Cs3MnBr5 nanocrystals (NCs) were optimized, with red and green emission. The doping of both phases with different lanthanides (Nd3+, Er3+, Tm3+ and Yb3+) was attempted, enabling an intense NIR emission only in CsMnBr3. Studying other perovskite compounds, CsPbX3 (with X = Br-, Cl-, I-) NCs were successfully synthesized using R-limonene as solvent. Then, the investigation of persistent luminescence (PeL) in Cs2NaInCl6:Mn2+ halide DPs demonstrated a dependence from the particles size: micrometric crystals presented a longer PeL than single crystals, whereas it disappeared in nanocrystals. Moreover, layered double perovskites (DPs) NCs with Cs4MnxCd1-xSb2Cl12 composition were synthesized. All the samples showed an absorption and a red emission stemming from Sb3+ and Mn2 (except for x = 0). Finally, the last project was the study of AECuSi4O10 (AE: Ca, Sr, Ba) silicates and their NIR photoemission, given by Cu2+.