Near-Infrared Emission in Low-Dimensional Halide Perovskite Derivatives: Cs2MX6 (M: Mo/W/Sn; X: Cl/Br) and (C8H12N)2PbBr4 with Doping

Abstract

Lead halide perovskites (APbX3, A: monovalent cation, X: Cl, Br, I) have been widely explored since last fifteen years due to their extraordinary optoelectronic properties. If the connectivity between metal-halide octahedra is lifted, the electronic dimensionality reduces successionally from 3D to 2D, 1D and 0D. This thesis focuses on such low-dimensional (0D and 2D) perovskite derivatives which emit in the near-infrared (NIR) region (900 – 1300 nm) through d-d and f-f electronic transitions. NIR emissions have several applications like non-invasive bio-imaging, food processing and therapy. NIR emissions are typically obtained from epitaxially grown III-V semiconductors, or colloidal PbS nanocrystals, or filament-based incandescent lamps. They have their own pros and cons. An alternative approach is to develop NIR emitting phosphors by Cr3+ (d-d transition) or lanthanides (f-f transitions) in halide or oxide-based hosts. But in that case, the excitation is high energy UV/blue light leading to thermalization losses. To address the issue, in chapter 2, we have shown all inorganic 0D perovskite derivatives Cs2MX6 (M: Mo/W; X: Cl/Br) have both excitation and emission in far-red (787 nm) and NIR (986 nm) region. By employing low-temperature (8 K) photoluminescence study, we found out that the excitation and emission happens through vibronically coupled d-d transitions. Then in order to dilute the NIR luminescent centers reducing concentration quenching, we doped W4+/ Mo4+ in another 0D system Cs2SnCl6, as discussed in Chapter 3. As a proof of concept, phosphor-converted light emitting diodes (pc-LED) were fabricated by coating these NIR phosphors on both 730 nm and 400 nm commercial LED chips. In Chapter 4, we explored the possibility of colloidal synthesis of Yb3+ doped phenylethylammonium lead bromide (PEA2PbBr4) 2D perovskites showing NIR emission at 997 nm because of f-f transition of Yb3+.