Third Harmonic Upconversion and Self-Trapped Excitonic Emission in 1D Pyridinium Lead Iodide

Hybrid lead halide perovskites have emerged as an important class of optoelectronic materials. A creative choice of "A"-site organic cations produces hybrid perovskites with reduced dimensionality and intriguing light-matter interactions. Nonlinear optical effects are expected to be stronger in one-dimensional (1D) lead halides compared to those in their 2D or 3D analogues due to greater quantum and dielectric confinements. We performed an extensive probe of the third harmonic generation (THG) properties in 1D pyridinium lead iodide single crystals for the first time. An efficient THG with a high laser-induced damage threshold is the highlight of this system. THG is selectively enhanced for excitation at an optical communication wavelength (1.5 mu m) corresponding to band gap resonance. A strong exciton-phonon interaction results in highly Stokes-shifted self-trapped excitonic emission in the 5-300 K temperature range. An interplay between anharmonicity and dynamic disorder dictates the emission properties, further complicated by an isostructural phase transition at 170 K.