Cesium lead halide perovskite materials have recently attracted attention in view of their optical and electronic properties which make them excellent candidates for potential applications in lasers, light emitting diodes and photodetectors. In this work, we provide the experimental and theoretical evidence for sequential photon absorption/re-emission in CsPbBr3 perovskite microwires. Using two-photon excitation, we recorded PL lifetimes and emission spectra as a function of the lateral distance between PL excitation and collection positions along the microwire, with separations exceeding 100 µm. As the propagation length increases, the PL spectrum develops a new emission peak that is red-shifted by 20 nm from the main emission and is accompanied by the appearance of the well-resolved rise times in the PL kinetics. We undertake quantitative modeling that accounts for bimolecular recombination and photon recycling within the microwire waveguide, and find that it is sufficient to account for the observed decay modifications. The model relies on a high radiative efficiency in CsPbBr3 perovskite microwires to explain the photon recycling observed. Such findings provide crucial information about the potential impact of photon recycling and waveguide trapping on optoelectronic properties of cesium lead halide perovskite materials
An intensity-modulated refractometer is proposed and experimentally demonstrated by using a long period fiber grating
(LPG) cascaded with a chirped-fiber Bragg grating (CFBG). The reflection wavelength band of the CFBG was properly
selected to contain the most sensitive spectral part of the LPG. As a result, intensity of the reflected signal was
modulated linearly by refractive index (RI) of surrounding liquid outside the LPG. RI measurement in a range from 1.33
to ~1.45 was realized with enhanced sensitivity up to 48.93 μW/R.I.U.
An optical fiber Fabry-Perot interferometer (FPI) coated with polyvinyl alcohol/poly-acrylic acid (PVA/PAA) hydrogel film for toxic gases measurement has been developed. Splicing a short section of hollow core fiber between two single mode fibers forms the FPI. Dip-coated pH-sensitive PVA/PAA hydrogel film on the fiber end performs as a receptor for binding of volatile acids or ammonia, which makes the sensing film swelling or shrinking and results in the dip wavelength shift of the FPI. By demodulating the evolution of reflection spectrum for various concentrations of volatile acids, a sensitivity of 20.8 nm/ppm is achieved with uniform linearity.
A novel magnetic field sensor by using an optical fiber Bragg grating (FBG) cascaded by a cleaved optical fiber end, which is face surrounded with magnetic fluid (MF), is experimentally demonstrated. Through Fresnel reflection (FR) of the fiber end face, side mode suppression ratio (SMSR) of reflection spectrum of the FBG is tuned by refractive index (RI) of the MF, which is sensitivity to the external magnetic field. As a result, magnetic field measurement is successfully achieved. Compared with previously reported methods based on FR of a fiber end only, it eliminates the influence of power level fluctuation of the optical source and therefore improves the measurement accuracy and stability. Furthermore, temperature can be measured simultaneously by monitoring wavelength shift of the FBG.
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