Rare-earth-containing halide and oxide perovskite nanomaterials are systematically reviewed for the first time, providing interdisciplinary challenges and opportunities to researchers.

luminescence, and also the recent hologram technique. [1-3] Compared to other conventional techniques, the fluorescence printing patterns supply promising high security to the key information valuable documents due to the tunable emission properties. [4,5] As counterfeiting technology has also been quickly developed, the traditional mono-mode anti-counterfeiting is far from the requirement of practical applications to guarantee a high level of data and information safety. The traditional anti-counterfeiting luminescence is achieved by the mono-mode downshifting (DS) luminescence, which converts the high energy photon into lower energy luminescence. To address such concern, developing more complicated anti-counterfeiting techniques by increasing the luminescent modes becomes the most challenging topic. Presently, the realization of concurrent upconversion (UC) and DS have been successfully utilized in anti-counterfeiting based on the lanthanide-based dopants. [6-9] The Eu-doped down-shift luminescent materials have been applied in the Euro banknotes, which enables the visible photoluminescence (PL) based on UV lamp excitation. Meanwhile, the Bank of China also introduced the Yb/Er-doped UC phosphors in the banknotes as the counterfeiting technique, which emits the Anti-counterfeiting techniques have become a global topic since they is correlated to the information and data safety, in which multimodal luminescence is one of the most desirable candidates for practical applications. However, it is a long-standing challenge to actualize robust multimodal luminescence with high thermal stability and humid resistance. Conventionally, the multimodal luminescence is usually achieved by the combination of upconversion and downshifting luminescence, which only responds to the electromagnetic waves in a limited range. Herein, the Yb 3+ /Er 3+ /Bi 3+ co-doped Cs 2 Ag 0.6 Na 0.4 InCl 6 perovskite material is reported as an efficient multimodal luminescence material. Beyond the excitation of ultraviolet light and nearinfrared laser (980 nm), this work extends multimodal luminescence to the excitation of X-ray. Besides the flexible excitation sources, this material also shows the exceptional luminescence performance, in which the X-ray detection limit reaches the level of nGy s −1 , indicating a great potential for further application as a colorless pigment in the anti-counterfeiting field. More importantly, the obtained double perovskite features high stability against both humidity and temperature up to 400 °C. This integrated multifunctional luminescent material provides a new directional solution for the development of multifunctional optical materials and devices.

Ultrathin 2D nanomaterials possess promising properties due to electron confinement within single or a few atom layers. As an emerging class of functional materials, ultrathin 2D rare‐earth nanomaterials may incorporate the unique optical, magnetic, and catalytic behaviors of rare‐earth elements into layers, exhibiting great potential in various applications such as optoelectronics, magnetic devices, transistors, high‐efficiency catalysts, etc. Despite its importance, reviews on ultrathin 2D rare‐earth nanomaterials or related topics are rare and only focus on a certain family of ultrathin 2D rare‐earth nanomaterials. This work is the first comprehensive review in this impressive field, which covers all families of ultrathin 2D rare‐earth nanomaterials, illustrating their compositions, syntheses, and applications. After summarizing the current achievements, the challenges and opportunities of future research on ultrathin 2D rare‐earth nanomaterials are evaluated.

The interplay between electronic correlations and topological protection may offer a rich avenue for discovering emergent quantum phenomena in condensed matter. However, electronic correlations have so far been little investigated in Weyl semimetals (WSMs) by experiments. Here, we report a combined optical spectroscopy and theoretical calculation study on the strength and effect of electronic correlations in a magnet Co 3 Sn 2 S 2. The electronic kinetic energy estimated from our optical data is about half of that obtained from single-particle ab initio calculations in the ferromagnetic ground state, which indicates intermediate-strength electronic correlations in this system. Furthermore, comparing the energy and side-slope ratios between the interband-transition peaks at high energies in the experimental and single-particle-calculation-derived optical conductivity spectra with the bandwidth-renormalization factors obtained by many-body calculations enables us to estimate the Coulomb-interaction strength (U ∼ 4 eV) in Co 3 Sn 2 S 2. Besides, a sharp experimental optical conductivity peak at low energy, which is absent in the single-particlecalculation-derived spectrum but is consistent with the optical conductivity peaks obtained by many-body calculations with U ∼ 4 eV, indicates that an electronic band connecting the two Weyl cones is flattened by electronic correlations and emerges near the Fermi energy in Co 3 Sn 2 S 2. Our work paves the way for exploring flat-band-generated quantum phenomena in WSMs.