Mechanism of Photoinduced Phase Segregation in Mixed-Halide Perovskite Microplatelets and Its Application in Micropatterning

Light Amplification in Fe-Doped CsPbBr3 Crystal Microwire Excited by Continuous-Wave Laser

Electrically pumped halide perovskite laser diodes remain unexplored, and it is widely acknowledged that continuous-wave (CW) lasing will be a crucial step. Here, we demonstrate room-temperature amplified spontaneous emission of Fe-doped CsPbBr₃ crystal microwire excited by a CW laser. Temperature-dependent photoluminescence spectra indicate that the Fe dopant forms a shallow level trap states near the band edge of the lightly doped CsPbBr₃ microcrystal. Pump intensity-dependent time-resolved PL spectra show that the introduced Fe dopant level makes the electron more stable in excited states, suitable for the population inversion. The emission peak intensity of the lightly Fe-doped microwire increases nonlinearly above a threshold of 12.3 kW/cm² under CW laser excitation, indicating a significant light amplification. Under high excitation, the uniform crystal structure and surface outcoupling in Fe-doped perovskite crystal microwires enhanced the spontaneous emission. These results reveal the considerable promise of Fe-doped perovskite crystal microwires toward low-cost, high-performance, room-temperature electrical pumping perovskite lasers.

Tunable Key-Size Physical Unclonable Functions Based on Phase Segregation in Mixed Halide Perovskites

Optical physical unclonable functions (PUFs) have been considered as an effective tool for anti-counterfeiting owing to the uncontrollable manufacturing process and excellent resistance to machine-learning attacks. However, most optical PUFs exhibit fixed challenge-response pairs and static encoding structures after they are manufactured, which significantly impedes the actual development. Herein, we propose a tunable key-size PUF based on reversible phase segregation in mixed halide perovskites with uncontrollable Br/I ratios under variable power densities. The basic performance of encryption keys of low and high power density was evaluated and indicated a high degree of uniformity, uniqueness, and readout repeatability. Merging the binary keys of low and high power density, tunable key-size PUF is realized with higher security. The proposed tunable key-size PUF offers new insights into the development of dynamic-structure PUFs and demonstrates a novel scheme for achieving higher security of anti-counterfeiting and authentication.

Snapshot multi-frame parallel spectral holographic microscopy based on a reconfigurable optical comb

We present a snapshot multi-frame parallel holographic microscopy system through a reconfigurable optical comb source, which consists of a digital micromirror device (DMD) based spectrum filter system and a spectroscopic Michelson interferometric system. The proposed system allows arbitrarily tuning comb spacing and comb number, and the capturing of multi-frame images without overlap in one exposure. As a result, high-quality spectral holograms can be obtained with less acquisition time. The performance of the system is detailed in the experiment and 45-wavelengths holographic imaging for perovskite micro-platelets is conducted, which proves the system has the ability to realize high-performance four-dimensional (4D) imaging.

Tunable Multicolor Fluorescence of Perovskite-Based Composites for Optical Steganography and Light-Emitting Devices

Multicolor fluorescence of mixed halide perovskites enormously enables their applications in photonics and optoelectronics. However, it remains an arduous task to obtain multicolor emissions from perovskites containing single halogen to avoid phase segregation. Herein, a fluorescent composite containing Eu-based metal-organic frameworks (MOFs), 0D Cs₄PbBr₆, and 3D CsPbBr₃ is synthesized. Under excitations at 365 nm and 254 nm, the pristine composite emits blue (B) and red (R) fluorescence, which are ascribed to radiative defects within Cs₄PbBr₆ and ⁵D₀→⁷F_J transitions of Eu³⁺, respectively. Interestingly, after light soaking in the ambient environment, the blue fluorescence gradually converts into green (G) emission due to the defect repairing and 0D-3D phase conversion. This permanent and unique photochromic effect enables anticounterfeiting and microsteganography with increased security through a micropatterning technique. Moreover, the RGB luminescence is highly stable after encapsulation by a transparent polymer layer. Thus, trichromatic light-emitting modules are fabricated by using the fluorescent composites as color-converting layers, which almost fully cover the standard color gamut. Therefore, this work innovates a strategy for construction of tunable multicolor luminescence by manipulating the radiative defects and structural dimensionality.