Antimony and bismuth ⟨111⟩ layered perovskites have recently attracted significant attention as possible, nontoxic alternatives to lead halide perovskites. Unlike lead halide perovskites, however, ⟨111⟩ halide perovskites have shown limited ability to tune their optical and electronic properties. Herein, we report on the metal alloying of manganese and copper into the family of materials with formula Cs 4 Mn 1−x Cu x Sb 2 Cl 12 (x = 0−1). By changing the concentration of manganese and copper, we show the ability to modulate the bandgap of this family of compounds over the span of 2 electron volts, from 3.0 to 1.0 eV. Furthermore, we show that in doing so, we can also adjust other relevant properties such as their magnetic behavior and their electronic structure.

We report the most direct experimental verification of Mott-Hubbard and Charge-Transfer insulators through X-ray emission spectroscopy in transition-metal fluorides. The p-d hybridization features in the spectra allow a straightforward energy alignment of the anion-2p and metal-3d valence states, which visually shows the difference between the two types of insulators. Further, in parallel with the theoretical Zaanen-Sawatzky-Allen diagram, a complete experimental systematics of the 3d Coulomb interaction and 2p-3d charge-transfer energy is reported, and could serve as a universal experimental trend for other transition-metal systems including oxides.

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Doppler-free optical double-resonance spectroscopy is used to study the   s p p 5 5 6 1 2 3 2 3 2 excitation sequence in room-temperature rubidium atoms. This involves a  s p 5 5 F or ±2 electric quadrupole transitions.

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Direct evidence of excitation of the 5p 3/2 → 6p 3/2 electric dipole forbidden transition in atomic rubidium is presented. The experiments were performed in a room temperature rubidium cell with continuous wave extended cavity diode lasers. Optical-optical double resonance spectroscopy with counterpropagating beams allows the detection of the non-dipole transition free of Doppler broadening. The 5p 3/2 state is prepared by excitation with a laser locked to the maximum F cyclic transition of the D2 line, and the forbidden transition is produced by excitation with a 911 nm laser. Production of the forbidden transition is monitored by detection of the 420 nm fluorescence that results from decay of the 6p 3/2 state. Spectra with three narrow lines (≈ 13 MHz FWHM) with the characteristic F − 1, F and F + 1 splitting of the 6p 3/2 hyperfine structure in both rubidium isotopes were obtained. The results are in very good agreement with a direct calculation that takes into account the 5s → 5p 3/2 preparation dynamics, the 5p 3/2 → 6p 3/2 non-dipole excitation geometry and the 6p 3/2 → 5s 1/2 decay. The comparison also shows that the electric dipole forbidden transition is a very sensitive probe of the preparation dynamics.PACS numbers: 32.70. Cs,32.70.Fw While the electric dipole approximation is a cornerstone in the study of the interaction between optical radiation fields and atoms, transitions induced by optical fields beyond this approximation have also become important tools in basic and applied studies of atoms. These so called "forbidden transitions" have been traditionally used in astrophysical and plasma studies [1]. They now play a fundamental role in metrology [2] and have also been used in experiments testing parity nonconserving interactions in atoms [3].In early studies of forbidden transitions, Sayer et al. [4] determined transition probabilities of electric quadrupole (E2) transitions using a tungsten lamp. The first direct observation of electric quadrupole effects in multiphoton ionization dates back to the work of Lambropoulos et al.[5]. Electric-dipole-forbidden transitions were exploited in three-wave-mixing experiments for optical sum and difference frequency generation in [6].The use of intense continuous-wave or pulsed laser sources has facilitated the observation of weak absorption lines. For instance, Tojo et al.[7] reported a determination of the oscillator strength of a E2 transition with a temperature-controlled cell and an extended cavity diode laser. Also, the study of strongly forbidden J = 0 → J = 0 transitions via single-photon excitation is presented in [8]. Excitation of forbidden transitions involving states with nonzero angular momentum in alkali atoms have also been studied over the last few years [9][10][11][12][13]. The coherent mixing of waves is theoretically studied in [9] for n 1 2 P − n 2 2 P transitions. The excitation of the 5p → 8p forbidden transition in thermal rubidium atoms was produced with a pulsed laser in [10] and using cold atoms in [12]. The experiment with co...

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We compare for the first time gas-phase 3s and 3p spectra from atomic Mn with corresponding spectra from the solid compounds MnF2 and MnO. These spectra are found to be strikingly similar, indicating that the solid-state spectra have a dominant origin in unscreened intra-atomic multiplet splittings, perhaps with correlation-induced satellites. Such outer-core hole states are thus not describable in terms of a simple superposition of fully screened and poorly screened spectra as recently proposed.PACS numbers: 79.60.Eq., 32.80.FbIn this Letter, we compare core-level photoelectron spectra of a free transition-metal atom with corresponding spectra from solid compounds for the first time in an attempt to resolve more precisely the exact nature of the multiplet splittings and final-state extra-atomic screening processes involved. We first discuss prior theoretical models for such effects and then consider our experimental data in this context.Multiplet splittings in transition-metal core-level binding energies have been known for some time. 1 " 5 For outer-core levels such as 3s and 3p in the 3d series, these effects in ionic and partially ionic materials were first interpreted in terms of a strongly intra-atomic L-S term splitting in the final state of the system with the core hole present. For the simplest case of 3s emission from a metal atom or ion with a ground-state spin of S, this splitting is due to the exchange interaction between the unpaired outermost 3d electrons and the remaining 3s electron. This model predicts a doublet with a separation which is proportional to [25 + 1] x [3s-3d exchange integral], a direct consequence of the Van Vleck theorem. 1,4,5 For intrashell interactions such as 3s-3d, 3p-3d, and 4y-4/, it was quickly realized that the splittings predicted by this model were too large by about a factor of 2, and that correlation effects beyond a simple Hartree-Fock-level approach could be responsible for this reduction in the observed separation between the two peaks. 1 " 3 Bagus, Freeman, and Sasaki 2 then showed that a more correct final-state wave function for an isolated Mn 2+ ion that included correlation in the final states via configuration interaction (CI) not only predicted well the reduction of the splitting of the dominant doublet in the 3s region for ionic compounds containing Mn 2+ , but also gave rise to additional lower-intensity satellite peaks at higher binding energies. These added features were then observed in high-resolution x-ray photoemission spectroscopy (XPS) experimental spectra from MnF 2 by Kowalczyk et A/., 3 and these results we reproduce in Fig. 1(b), together with the predicted heights and positions from the CI calculations, which are shown in Fig. 1(d). The calculated heights are derived here from the assumption that, at typical XPS excitation Units] ITY (Arb. 2 LU Z