The incorporation of impurity ions or doping is a promising method for controlling the electronic and optical properties and the structural stability of halide perovskite nanocrystals (NCs). Herein, we establish relationships between rare‐earth ions doping and intrinsic emission of lead‐free double perovskite Cs2AgInCl6 NCs to impart and tune the optical performances in the visible light region. Tb3+ ions were incorporated into Cs2AgInCl6 NCs and occupied In3+ sites as verified by both crystallographic analyses and first‐principles calculations. Trace amounts of Bi doping endowed the characteristic emission (5D4→7F6‐3) of Tb3+ ions with a new excitation peak at 368 nm rather than the single characteristic excitation at 290 nm of Tb3+. By controlling Tb3+ ions concentration, the emission colors of Bi‐doped Cs2Ag(In1−xTbx)Cl6 NCs could be continuously tuned from green to orange, through the efficient energy‐transfer channel from self‐trapped excitons to Tb3+ ions. Our study provides the salient features of the material design of lead‐free perovskite NCs and to expand their luminescence applications.

The anti-site defect model was established to investigate transposition influence on the optical and electronic properties of the double-perovskite Cs2AgSbCl6.

Recently, lead-based perovskite materials with the formula APbX 3 (A = Cs, methylammonium; X = Cl, Br, I) have received broad attention for their excellent optical and electronic properties in the fields of photovoltaic solar cells, [1] light-emitting diodes (LEDs), [2] sensitive photodetectors, [3] etc. However, the presence of toxic lead and unsatisfactory stability against heat and humidity restrict their further application. [4] An effective method to solve these issues is to replace divalent Pb with tetravalent Sn, forming a molecular salt structure with the formula A 2 SnX 6 (X = Cl, Br, I), which is a 50% Sn defect perovskite derivative featuring isolated [SnX 6 ] 2− octahedra. [5] This substitution can not only result in long-term stability in air but also maintain the high-symmetry cubic structure with a different halogen X Lead-free and stable Sn halide perovskites demonstrate tremendous potential in the field of optoelectronic devices. Here, the structure and optical properties of the "defect" perovskites Cs 2 SnCl 6−x Br x are reported, as well as their use as photodetector materials. Millimeter-sized Cs 2 SnCl 6−x Br x single crystals are grown by the hydrothermal method, with the body color continuously changing from transparent to yellow and finally to dark red. Narrowband single-crystal photodetectors using Cs 2 SnCl 6−x Br x crystals are presented, which show a high detectivity of ≈2.71 × 10 10 Jones, with narrowband photodetection (full-width at half-maximum ≈45 nm) and high ion diffusion barriers. Moreover, the response spectra are continuously tuned from near violet to orange depending on the variation of the bandgap of the single crystals by changing the halide compositions. The strong surface charge recombination of the excess carriers near the crystal surfaces produced by short wavelength light elucidates the narrowband photodetection behavior. This work provides a new paradigm in the design of lead-free, stable, and high-performance perovskite derivatives for optoelectronics applications.

their excellent optoelectronic properties including long carrier diffusion lengths, large absorption coefficients, and remarkable photovoltaic, photodetector, and light-emitting performance. [1] Although much progress has been made, the toxicity of lead is detrimental to the environment and human body. [2] Accordingly, the search for lead-free alternatives has attracted many attentions. One of the most popular methods is the substitution of two divalent Pb 2+ by a monovalent cation and a trivalent cation to form a double perovskite structure with a basic formula (A 2 (B + ,B. 3+ )X 6 ) (A = Cs + ;The double perovskite materials were previously proposed in 1970 since they can be used as ferroelectric materials, such as Cs 2 NaBiCl 6 . [4] In the light of the intense interest in halide perovskites, versatile new lead-free halide double perovskites have been predicted and synthesized, and some of which can grow into single crystals or nanocrystals. Moreover, halide double perovskites have been used as sensitive and fast UV photodetectors, solar cell A 2 (B + ,B 3+ )X 6 can overcome the lead toxicity and enable generally large band gap engineering via B/B sites' transmutation or exotic dopants to fulfill the emerging applications in the optoelectronic fields. Herein, the design and the experimental synthesis of a new family of Mn 2+ -doped Cs 2 NaBi 1-x In x Cl 6 crystals with an intense orangeyellow emission band are reported, and the phase formation stability is discussed via a combined experimental-theoretical approach. Depending on the manipulation of Bi 3+ /In 3+ combination, the band gap increases with In 3+ content, and a subsequent evolution from indirect to direct band gap is verified. The halide double perovskite family represented by

Semiconducting molybdenum ditelluride (2H-MoTe 2 ), a two-dimensional (2D) transition metal dichalcogenide, has attracted extensive research attention due to its favorable physical properties for future electronic devices, such as appropriate bandgap, ambipolar transport characteristic, and good chemical stability. The rational tuning of its electronic properties is a key point to achieve MoTe 2 -based complementary electronic and optoelectronic devices. Herein, we demonstrate the dynamic and effective control of the electronic properties of few-layer MoTe 2 , through the in situ surface modification with aluminum (Al) adatoms, with a view toward high-performance complementary inverter devices. MoTe 2 is found to be significantly electron doped by Al, exhibiting a continuous transport transition from p-dominated ambipolar to n-type unipolar with enhanced electron mobility. Using a spatially controlled Al doping technique, both p-and n-channels are established on a single MoTe 2 nanosheet, which gives complementary inverters with a record-high gain of ∼195, which stands out in the 2D family of materials due to the balanced p-and n-transport in Al-modified MoTe 2 . Our studies coupled with the tunable nature of in situ modification enable MoTe 2 to be a promising candidate for high-performance complementary electronics.