In this work, Mn 2+ has been efficiently and homogeneously doped into two-dimensional (2D) distorted single-layered EA 2 PbBr 4 (EA: ethylammonium) via a reprecipitation method. Both the doped and undoped 2D layered lead halide perovskites (LHPs) were characterized using a combination of X-ray, electron microscopy, and spectroscopy techniques. The Mn 2+ -doped EA 2 PbBr 4 (EA 2 PbBr 4 :Mn 2+ ) shows a 78% photoluminescence (PL) quantum yield (QY) with complete quenching of self-trapped exciton emission because of efficient exciton trapping by defects created by dopants and small activation energy (∼9.8 meV) between the defect states and Mn 2+ d states. Compared to the long lifetime (∼1.5 ms) of Mn 2+ emission in CsPbCl 3 , the lifetime in 2D EA 2 PbBr 4 is found to be ∼0.75 ms, resulting from the heavy atom effect. Additionally, the PL QY of Mn 2+ emission can be further increased by codoping Zn 2+ or Cd 2+ , which is attributed to a high density of trap states created by codoping, facilitating exciton to Mn 2+ energy transfer. These results reveal the key role of trap states in the energy transfer of Mn 2+ -doped 2D LHPs.

Antimony-based metal halide hybrids have attracted enormous attention due to the stereoactive 5s2 electron pair that drives intense triplet broadband emission. However, energy/charge transfer has been rarely achieved for Sb3+-doped materials. Herein, Sb3+ ions are homogeneously doped into 2D [NH3(CH2)4NH3]­CdBr4 perovskite (Cd-PVK) using a wet-chemical method. Compared to the weak singlet exciton emission of Cd-PVK at 380 nm, 0.01% Sb3+-doped Cd-PVK exhibits intense triplet emission located at 640 nm with a near-unity quantum yield. Further increasing the doping concentration of Sb3+ completely quenches singlet exciton emission of Cd-PVK, concurrently with enhanced Sb3+ triplet emission. Delayed luminescence and femtosecond-transient absorption studies suggest that Sb3+ emission originates from exciton transfer (ET) from Cd-PVK host to Sb3+ dopant, while such ET cannot occur with Pb2+-doped Cd-PVK because of the mismatch of energy levels. In addition, density function theory calculations indicate that the introduced Sb3+ likely replace the Cd2+ ions along with the deprotonation of butanediammonium for charge balance, instead of generating Cd2+ vacancies. This work provides a deeper understanding of the ET of Sb3+-doped Cd-PVK and suggests an effective strategy to achieve efficient triplet Sb3+ emission beyond 0D Cl-based hybrids.

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All-fiber magnetic-field sensor based on a device consisting of a microfiber knot resonator and magnetic fluid is proposed for the first time in this Letter. Sensor principles and package technology are introduced in detail. Experimental results show that the resonance wavelength of the proposed sensor regularly varies with changes to the applied magnetic field. When the magnetic field is increased to 600 Oe, the wavelength shift reaches nearly 100 pm. Moreover, the sensor responding to the 50 Hz alternating magnetic field is also experimentally investigated, and a minimal detectable magnetic-field strength of 10 Oe is successfully achieved.

In this work, a new two-dimensional Cd-based (F 2 CHCH 2 NH 3 ) 2 CdBr 4 perovskite (Cd−P) with indirect bandgap and a direct Pb-based (F 2 CHCH 2 NH 3 ) 2 PbBr 4 (Pb−P) are successfully synthesized with isostructural features. Compared to the blueish white light emission of Pb−P, almost no white light can be observed for Cd−P due to the forbidden transition of self-trapped exciton (STE) emission. Interestingly, the white light emission of Cd x Pb 1−x −P (x represents the feed ratio of Cd) is significantly improved with the photoluminescence (PL) quantum yield (QY) raising from <1% to 32.5% by alloying these two isostructural perovskites, which is attributed to the breaking of selection rules for forbidden transitions of STEs with Jahn−Teller like octahedral distortion, as suggested by the results from density functional theory (DFT) calculations and time-resolved spectroscopies. This study demonstrates the intriguing effect of alloying on activating STE emission as an effective approach to control and enhance the optical properties of metal halide perovskites.