Spectroscopy of Cr3+^{\bf{3+}} in ferroelectric ceramics lead-lanthanum zirconate-titanate-x/95/5 with Lanthanum content xx = 0.5 to 4 wt %

The study shows the importance of internal optical transitions $^{2}{\rm E} \to^{4}$A$_{2}$ of the excited Cr$^{3+}$ ions used as a probe of the ceramics in the microscopic scale. The results are interpreted in terms of Cr$^{3+}$ luminescent centres and simultaneous vibrational excitations of the lattice. In presence of thermally activated disorder, the PLZT-x/95/5 ferroelectric ceramics lead to interesting spectral variations with temperature by appearance of certain vibronic sidebands observed around the pure electronic transitions. The phononic origin of the process is analysed in terms of lattice perturbation in the environment of the Cr$^{3+}$ sites

Unraveling exciton–phonon coupling in individual FAPbI3 nanocrystals emitting near-infrared single photons

Formamidinium lead iodide (FAPbI3) exhibits the narrowest bandgap energy among lead halide perovskites, thus playing a pivotal role for the development of photovoltaics and near-infrared classical or quantum light sources. Here, we unveil the fundamental properties of FAPbI3 by spectroscopic investigations of nanocrystals of this material at the single-particle level. We show that these nanocrystals deliver near-infrared single photons suitable for quantum communication. Moreover, the low temperature photoluminescence spectra of FAPbI3 nanocrystals reveal the optical phonon modes responsible for the emission line broadening with temperature and a vanishing exciton–acoustic phonon interaction in these soft materials. The photoluminescence decays are governed by thermal mixing between fine structure states, with a two-optical phonon Raman scattering process. These results point to a strong Frölich interaction and to a phonon glass character that weakens the interactions of charge carriers with acoustic phonons and thus impacts their relaxation and mobility in these perovskites