High-efficiency upconversion luminescence in UCNPs/CsPbBr3 nanocomposites enhanced by silver nanoparticles.

Upconversion nanocomposites with multiple light-emitting centers have attracted great attention as functional materials, but their low efficiency limits their further applications. Herein, a novel, to the best of our knowledge, system for nanocomposites consisting of upconversion nanoparticles (UCNPs) and perovskite quantum dots (PeQDs) assembled with Ag nanoparticles (NPs) is proposed. Upconversion luminescence (UCL) operation from PeQDs is triggered by near-infrared (NIR) sensitization through Förster resonance energy transfer (FRET) and photon reabsorption (PR). Especially, the photoluminescence (PL) emission efficiency is found to be significantly enhanced due to the increased energy transfer efficiency and radiative decay rate in the UCNPs/CsPbBr3 nanocomposites. The results offer new opportunities to improve the UCL properties of perovskites and open new development in the fields of LED lighting, solar cells, biomedicine, and so on.

Multi-color UCNPs/CsPb(Br1-xIx)3 for upconversion luminescence and dual-modal anticounterfeiting.

Advanced hybrid materials have attracted extensive attention in optoelectronics and photonics application due to their unique and excellent properties. Here, the multicolor upconversion luminescence properties of the hybrid materials composed of CsPbX3(X = Br/I) perovskite quantum dots and upconversion nanoparticles (UCNPs, core-shell NaYF4:25%Yb3+,0.5%Tm3+@NaYF4) is reported, achieving the upconversion luminescence with stable and bright of CsPbX3 perovskite quantum dots under 980 nm excitation. Compared with the nonlinear upconversion of multi-photon absorption in perovskite, UCNPs/CsPbX3 achieves lower power density excitation by using the UCNPs as the physical energy transfer level, meeting the demand for multi-color upconversion luminescence in optical applications. Also, the UCNPs/CsPbX3 combined with ultraviolet curable resin (UVCR) shows excellent water and air stability, which can be employed as multicolor fluorescent ink for screen printing security labels. Through the conversion strategy, the message of the security labels can be encrypted and decrypted by using UV light and a 980 nm continuous wave excitation laser as a switch, which greatly improves the difficulty of forgery. These findings provide a general method to stimulate photon upconversion and improve the stability of perovskite nanocrystals, which will be better applied in the field of anti-counterfeiting.

Synergistic luminescence effect and high-pressure optical properties of CsPbBr2Cl@EuMOFs nanocomposites.

Metal-organic frameworks (MOFs) are a class of highly porous materials that have garnered significant attention in the field of optoelectronics due to their exceptional properties. In this study, CsPbBr2Cl@EuMOFs nanocomposites were synthesized using a two-step method. The fluorescence evolution of the CsPbBr2Cl@EuMOFs was investigated under high pressure, revealing a synergistic luminescence effect between CsPbBr2Cl and Eu3+. The study found that the synergistic luminescence of CsPbBr2Cl@EuMOFs remains stable even under high pressure, and there is no energy transfer among different luminous centers. These findings provide a meaningful case for future research on nanocomposites with multiple luminescent centers. Additionally, CsPbBr2Cl@EuMOFs exhibit a sensitive color-changing mechanism under high pressure, making them a promising candidate for pressure calibration via the color change of the MOF materials.

STED microscopy reveals in-situ photoluminescence properties of single nanostructures in densely perovskite thin films.

All-inorganic perovskite nanomaterials have attracted much attention recently due to their prominent optical performance and potential application for optoelectronic devices. The carriers dynamics of all-inorganic perovskites has been the research focus because the understanding of carriers dynamics process is of critical importance for improving the fluorescence conversion efficiency. While photophysical properties of excited carrier are usually measured at the macroscopic scale, it is necessary to probe the in-situ dynamics process at the nanometer scale and gain deep insights into the photophysical mechanisms and their localized dependence on the thin-film nanostructures. Stimulated emission depletion (STED) nanoscopy with super-resolution beyond the diffraction limit can directly provide explicit information at a single particle level or nanometer scale. Through this unique technique, we firstly study the in-situ dynamics process of single CsPbBr3 nanocrystals(NCs) and nanostructures embedded inside high-dense samples. Our findings reveal the different physical mechanisms of PL blinking and antibunching for single CsPbBr3 NCs and nanostructures that correlate with thin-film nanostructural features (e.g. defects, grain boundaries and carrier mobility). The insights gained into such nanostructure-localized physical mechanisms are critically important for further improving the material quality and its corresponding device performance.

Photocontrol of a microbubble in a fiber-based hollow microstructure.

We experimentally demonstrated a novel photocontrol scheme of a microbubble. The microbubble was confined in a fiber-based hollow microstructure and its movement was driven by the laser-induced photothermal Marangoni force. The position of the microbubble was controlled at a micrometer scale by simply adjusting the drive laser power. This scheme permitted the firsthand control of a microbubble with a divergent single laser beam. As a practical demonstration, we proposed a variable fiber all-optical attenuator by exploiting the total internal reflection on the surface of the photo-controlled microbubble to modulate the target light beam. The experimental results showed that such a compact fiber attenuator possessed a low insertion loss of 0.83 dB, a maximum extinction ratio of 28.7 dB, and had potential to be integrated into the lab-on-a-chip for the modulation of the light beam power.

Ultracompact fiber all-optical router using a photo-controlled microbubble.

An ultracompact fiber router based on a photo-controlled microbubble was proposed in this Letter. Because the microbubble can be repositioned precisely in the fiber microcavity by adjusting the drive laser power, the target light beam that was incident on the gas-liquid interface of the microbubble was routed toward different directions by the light refraction inside the photo-controlled microbubble. Experimental results showed that the device had a low insertion loss of 0.64 dB, response time of (1.2-1.8s), and can achieve the continuous beam redirections within an angle range of 56° by exploiting a drive laser power of only 1.8 mW. With the characteristics of excellent controllability, low consumption, and no electromechanical parts, such a fiber all-optical router has potential to be used for the multiplex treatments and analysis applications of the photonic laboratory on a chip (PLOC).

Laser-induced suspension of a microbubble in a liquid-filled fiber microcavity for large-range tilt sensing.

In this Letter, we propose a compact fiber tilt sensor based on a microbubble suspended in a liquid-filled microcavity at the end of a single-mode fiber. By coupling a single-frequency laser with enough power, the microbubble could suspend in the microcavity due to the Marangoni effect, which constitutes a Fabry-Perot interferometer. When the tilt angle changes, the position of the microbubble changes as well, which causes the variation of the dominant frequency of the interference fringes in the spectrum. The experimental results show that the tilt angle sensitivity of the sensor reaches ${3.64} \times {{10}^{ - 4}}\;{{\rm nm}^{ - 1}}/{\rm Deg}$3.64×10-4nm-1/Deg at a wide sensing range from ${-}{45}^\circ $-45∘ to 45° with a good repeatability.

Temperature-insensitive optical fiber strain sensor with ultra-low detection limit based on capillary-taper temperature compensation structure.

An optical fiber strain sensor based on capillary-taper compensation structure was proposed. The theoretical simulation by using the finite element analysis method shows a matching condition between the capillary length and the interference-cavity length to achieve the zero temperature crosstalk. Meanwhile, the strain sensitivity can also be improved greatly at the matching condition. We then set up an insertion controller system with high accuracy to make sure the interference-cavity length can match the capillary length. Finally the fiber strain sensor with both ultra-low temperature-crosstalk (0.05 pm/°C) and ultra-high sensitivity (214.35 pm/µÎµ) was achieved, and the experimental results agreed well with the calculated results. The "ladder-mode" and repeatability experiments showed that the proposed sensor was actually with the ultra-low detection limit of 0.047 µÉ›.

Ultrasensitive fiber tilt sensor based on a mobile inscribed microbubble along the arc-shaped inwall of the microcavity: publisher's note.

This publisher's note corrects an error in the funding section in Opt. Lett.42, 4418 (2017).OPLEDP0146-959210.1364/OL.42.004418.

Compact optical fiber temperature sensor with high sensitivity based on liquid-filled silica capillary tube.

We propose a highly sensitive fiber temperature sensor based on a section of liquid-sealed silica capillary tube inserted in a single-multi-single-mode fiber structure. The liquid polymer is filled into the silica capillary tube through two micro-holes drilled by a femtosecond laser. Then the micro-holes are blocked by UV curable adhesive with ultra-small volume. Obvious Mach-Zehnder interference peaks were shown in its transmission spectrum. The proposed fiber temperature sensor can be reliably used for actual point detection owing to its high sensitivity (8.09 nm/°C), good linearity (99.93%), compact size, good mechanical property, high fabrication efficiency, and good repeatability and stability.

Quantitative microfluidic delivery based on an optical breakdown-driven micro-pump for the fabrication of fiber functional devices.

An optical breakdown-driven micro-pump was reported to deliver the quantitative liquid to the fiber microstructure efficiently. The amount of the pumped liquid can be controlled by adjusting the irradiation time of the femtosecond laser pulses. Such a method of microfluidic delivery has potential for the fabrication of fiber functional devices and the rapid injection of analytes into a lab-in-fiber for chemical and biological analysis. As a demonstration, a fiber spirit level based on a mobile microbubble was achieved by pumping nanoliter scale liquid into a fiber micro-cavity with this method.

Compact fiber biocompatible temperature sensor based on a hermetically-sealed liquid-filling structure.

A compact and robust fiber temperature sensor based on a hermetically-sealed liquid-filling Fabry-Perot (FP) cavity was fabricated by low-cost but efficient processes, including fusion splicing, liquid injection, and fused tapering. Owing to the high thermal optical coefficient (TOC) of the ethanol, the optical path difference (OPD) in the FP cavity varied strongly with temperature, which consequently induced a drastic wavelength shift of the reflection spectrum. Meanwhile, the low freezing point of the ethanol caused the fiber sensor to have the ability of detecting the sub-zero temperatures. As a result, a linear sensitivity as high as 429 pm/°C was achieved in the range between -5 °C and 30 °C. In addition, our fiber temperature sensor also exhibited rapid response time, good repeatability, and stability. The biocompatible structure, low fabrication cost, and high performance of such a temperature sensor can provide it potential for biological applications.

Ultrasensitive fiber tilt sensor based on a mobile inscribed microbubble along the arc-shaped inwall of the microcavity.

We report a novel fiber tilt sensor based on a mobile microbubble inscribed in an ellipsoidal liquid-filled microcavity. When the tilt angle changes, the microbubble in the liquid can drift along the upper arc-shaped inwall of the microcavity and stay at a vertex to get a state of mechanical equilibrium. The drifting microbubble induces a drastic change on the optical path difference between the light beams in the microcavity and, consequently, on the reflection spectrum, which makes it a tilt angle sensitive element. The experimental results show that the tilt angle sensitivity is as high as 160.21 nm/deg, and the detection resolution of such a sensor can reach up to 2.3×10-3 deg. Moreover, such a fiber tilt sensor is capable of distinguishing the tilt direction, since the movement of the microbubble is tilt direction dependent.

Highly sensitive temperature sensor based on cascaded polymer-microbubble cavities by employing a subtraction between reciprocal thermal responses.

A miniature, robust, and highly sensitive optical fiber temperature sensor based on cascaded polymer-microbubble cavities was fabricated by polymer-filling and subsequent heat-curing process. The expansion of polymer cavity results in the compression of microbubble cavity when the sensor is heated. We demodulated the interference spectrum by means of the fast-Fourier transform (FFT) and signal filtering. Since the thermal response of the polymer cavity is positive and that of the microbubble cavity is negative, a high sensitivity of the temperature sensor is achieved by a subtraction between the two reciprocal thermal responses. Experimental results show that the sensitivity of the temperature sensor is as high as 5.013 nm/°C in the measurement range between 20 °C and 55 °C. Meanwhile, such a sensor has potential for mass production, owing to the simple, nontoxic, and cost-effective process of fabrication.

Pressure-induced distinct excitonic properties of 2D perovskites with isomeric organic molecules for spacer cations.

Spacer organic cations in two-dimensional (2D) perovskites play vital roles in inducing structural distortion of the inorganic components and dominating unique excitonic properties. However, there is still little understanding of spacer organic cations with identical chemical formulas, and different configurations have an impact on the excitonic dynamics. Herein, we investigate and compare the evolution of the structural and photoluminescence (PL) properties of [CH3(CH2)4NH3]2PbI4 ((PA)2PbI4) and [(CH3)2CH(CH2)2NH3]2PbI4 ((PNA)2PbI4) with isomeric organic molecules for spacer cations by combining steady-state absorption, PL, Raman and time-resolved PL spectra under high pressures. Intriguingly, the band gap is continuously tuned under pressure and decreased to 1.6 eV at 12.5 GPa for (PA)2PbI4 2D perovskites. Simultaneously, multiple phase transitions occur and the carrier lifetimes are prolonged. In contrast, the PL intensity of (PNA)2PbI4 2D perovskites exhibits an almost 15-fold enhancement at 1.3 GPa and an ultrabroad spectral range of up to 300 nm in the visible region at 7.48 GPa. These results indicate that the isomeric organic cations (PA+ and PNA+) with different configurations significantly mediate distinct excitonic behaviors due to different resilience to high pressures and reveal a novel interaction mechanism between organic spacer cations and inorganic layers under compression. Our findings not only shed light on the vital roles of isomeric organic molecules as organic spacer cations in 2D perovskites under pressure, but also open a route to rationally design highly efficient 2D perovskites incorporating such spacer organic molecules in optoelectronic devices.

Revealing photoluminescence mechanisms of single CsPbBr3/Cs4PbBr6 core/shell perovskite nanocrystals.

CsPbBr3 nanocrystals (NCs) encapsulated by Cs4PbBr6 has attracted extensive attention due to good stability and high photoluminescence (PL) emission efficiency. However, the origin of photoluminescence (PL) emission from CsPbBr3/Cs4PbBr6 composite materials has been controversial. In this work, we prepare CsPbBr3/Cs4PbBr6 core/shell nanoparticles and firstly study the mechanism of its photoluminescence (PL) at the single-particle level. Based on photoluminescence (PL) intensity trajectories and photon antibunching measurements, we have found that photoluminescence (PL) intensity trajectories of individual CsPbBr3/Cs4PbBr6 core/shell NCs vary from the uniform longer periods to multiple-step intensity behaviors with increasing excitation level. Meanwhile, second-order photon correlation functions exhibit single photon emission behaviors especially at lower excitation levels. However, the PL intensity trajectories of individual Cs4PbBr6 NCs demonstrate apparent "burst-like" behaviors with very high values of g 2(0) at any excitation power. Therefore, the distinguishable emission statistics help us to elucidate whether the photoluminescence (PL) emission of CsPbBr3/Cs4PbBr6 core/shell NCs stems from band-edge exciton recombination of CsPbBr3 NCs or intrinsic Br vacancy states of Cs4PbBr6 NCs. These findings provide key information about the origin of emission in CsPbBr3/Cs4PbBr6 core/shell nanoparticles, which improves their utilization in the further optoelectronic applications.