Semiconductors group

Abstract:

Recently, Bi-doped Cs₂ Ag_0.6 Na_0.4 InCl₆ lead-free double perovskites demonstrating efficient warm-white emission have been reported. To enable the solution processing and enrich the application fields of this promising material, here a colloidal synthesis of Cs₂ Ag_{1- x} Na_x In_{1- y} Bi_y Cl₆ nanocrystals is further developed. Different from its bulk states, the emission color temperatures of the nanocrystal can be tuned from 9759.7 to 4429.2 K by Na⁺ and Bi³⁺ incorporation. Furthermore, the newly developed nanocrystals can break the wavefunction symmetry of the self-trapped excitons by partial replacement of Ag⁺ ions with Na⁺ ions and consequently allow radiative recombination. Assisted with Bi³⁺ ions doping and ligand passivation, the photoluminescence quantum yield of the Cs₂ Ag_0.17 Na_0.83 In_0.88 Bi_0.12 Cl₆ nanocrystals is further promoted to 64%, which is the highest value for lead-free perovskite nanocrystals at present. The new colloidal nanocrystals with tunable color temperature and efficient photoluminescence are expected to greatly advance the research progress of lead-free perovskites in single-emitter-based white emitting materials and devices.

Abstract:

Combination of a cryogenic ion-trap machine, operated at 4.7 K, with the free-electron-laser FELIX allows the first experimental characterization of the unusually bright antisymmetric stretch (ν₃) and π-bending (ν₂) fundamentals of the He–X⁺–He (X = H, D) chromophore of the in situ prepared HHe_n⁺ and DHe_n⁺ (n = 3–6) complexes. The band origins obtained are fully supported by first-principles quantum-chemical computations, performed at the MP2, the CCSD(T), and occasionally the CCSDTQ levels employing extended basis sets. Both the experiments and the computations are consistent with structures for the species with n = 3 and 6 being of T-shaped C_2v and of D_4h symmetry, respectively, while the species with n = 4 are suggested to exhibit interesting dynamical phenomena related to large-amplitude motions.