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Thermal photoluminescence (PL) quenching is fundamentally important for perovskite optoelectronic applications. Herein, we investigated PL characteristics of CsSnBr3 microsquares and micropyramids ...

The development of hole-transport layers (HTLs) that elevate charge extraction, improve perovskite crystallinity, and decrease interfacial recombination is extremely important for enhancing the performance of inverted perovskite solar cells (PSCs). In this work, the nanoporous nickel oxide (NiO x ) layer as well as NiO x thin film was prepared via chemical bath deposition as the HTL. The sponge-like structure of the nanoporous NiO x helps to grow a pinhole-free perovskite film with a larger grain size compared to the NiO x thin film. The downshifted valence band of the nanoporous NiO x HTL can improve hole extraction from the perovskite absorbing layer. The device based on the nanoporous NiO x layer showed the highest efficiency of 13.43% and negligible hysteresis that was better than the one using the NiO x thin film as the HTL. Moreover, the PSCs sustained 80% of their initial efficiency after 50 days of storage. This study provides a powerful strategy to design PSCs with high efficiency and long-term stability for future production.

To realize the refractive index dispersion accurately is essential for the design of optical devices. In this paper, we study hexagonal ZnO microrod cavities. We measure angle-resolved photolumines...

Two new phosphine ligands, diphenylmethylphosphine (DPMP) and triphenylphosphine (TPP), were introduced onto cesium lead bromoiodide nanocrystals (CsPbBrI2 NCs) to improve air stability in the ambient atmosphere. Incorporating DPMP or TPP ligands can also enhance film-forming and optoelectronic properties of the CsPbBrI2 NCs. The results reveal that DPMP is a better ligand to stabilize the emission of CsPbBrI2 NCs than TPP after storage for 21 days. The increased carrier lifetime and photoluminescence quantum yield (PLQY) of perovskite NCs are due to the surface passivation by DPMP or TPP ligands, which reduces nonradiative recombination at the trap sites. The DPMP and TPP-treated CsPbBrI2 NCs were successfully utilized as red emitters for fabricating perovskite light-emitting diodes with enhanced performance and prolonged device lifetime relative to the pristine one.

Nontoxic metal-halide perovskite materials have triggered a revolution of emitting devices as well as solar cells. In this work, we demonstrate a lead-free γ-CsSnI3 perovskite random lasing operate...

In this study, we designed a substrate-free surface plasmon polariton laser composed of ZnO nanowire and aluminum. As a result, we successfully transfer device to another substrate and produced the laser.

The CsPbBr3 microwires with unique isosceles right triangle cross-sections are commonly observed via chemical vapor deposition method. In this work, we study the correlations between measured multi-mode lasing behaviors and the simulation of the mode patterns inside the triangular-rod microcavity. We confirm that lasing action with higher-order transverse modes can well sustain, even when these modes experience large optical loss due to the isosceles triangle cross-section. By comparing the experimental and simulation results, the higher-order transverse modes tend to show up prior to the fundamental transverse modes for wider microwires. We attribute this behavior to the nonuniform field distribution caused by the high absorption efficiency of CsPbBr3. We also elaborate on the difficulties to sustain the whispering gallery mode in the CsPbBr3 triangular-rod microcavity, which implies that the lateral dimension and geometry of the cavity should be considered carefully for the future design of low threshold wire-based laser devices.

We present the growth of ZnO nanorods (NRods) prepared by chemical bath deposition on 100 nm and 200 nm ZnO seed layer sputtered on glass substrate. The structural and optical properties of ZnO NRods were investigated by Field Emission Scanning Electron Microscope (FESEM), energy-dispersive X-ray (EDX), X-Ray Diffraction (XRD), and UV-Visible (UV-Vis) analyses. Random lasing (RL) emission behaviour was characterized by pulsed-wave micro-photoluminescence (pw µ-PL) analysis. Changed in seed layer thickness on 100 nm and 200 nm, allowing for greater particle size of ZnO NRods to form, while maintaining the preferred diffraction of self-organized growth direction with high-quality c-plane. The reduction in optical properties of ZnO NRods also lowering random lasing emission threshold toward higher excitation power density from 37.86 kW/cm2 to 95.40 kW/cm2.

The thermal deposition of lead iodide (PbI2) results in the changes in the contact surface of a poly (3,4-ethylenedioxythiophene) poly (styrene sulfonate) (PEDOT:PSS) layer of solar cells (SCs). The changed contact surface of PEDOT:PSS layer after the thermal deposition of PbI2 remains stable after PbI2 is converted into perovskite and leaves the degraded perovskite/PEDOT:PSS interface. The degraded perovskite/pristine PEDOT:PSS interface leads to a low power conversion efficiency (η%) of SCs at 3.84%. The properties of the contact surface of the PEDOT:PSS layer during the thermal deposition of PbI2 can be retained by treating PEDOT:PSS with dimethyl sulfoxide (DMSO) and maintain the perovskite/PEDOT:PSS interface in good condition after PbI2 is converted. Perovskite SCs with DMSO-treated PEDOT:PSS substantially improves η% from 3.84% to 9.58%.

In this research, we demonstrate regular-type perovskite solar cells based on tungsten trioxide nanoparticles layer (WO3 NL) as the electron transport layer and methylammonium lead iodide nanowires (MAPbI3 NWs) as the absorbing layer. By adjusting the amount of the anti-solvent DMF, MAPbI3 NWs with different diameters ranging from 50 to 100 nm and lengths extending to several micrometers were obtained. [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) and cesium carbonate (Cs2CO3) were introduced between WO3 NL and MAPbI3 NWs to improve film morphology and charge transfer ability. Meanwhile, spiro-MeOTAD doped with bis(trifluoromethane)sulfonimide lithium salt (Li-TFSI) was utilized to enhance hole transport. Finally, the perovskite solar cells with the configuration of ITO/WO3 NL/Cs2CO3/PCBM/MAPbI3 NWs/spiro-MeOTAD/Au were fabricated and evaluated. To date, perovskite NWs treating with the proper amount of the anti-solvent DMF possess higher absorption, faster carrier transportation and lower recombination that are responsible for photovoltaic application.

We realized a single-mode laser with an ultra-high quality factor in individual cesium lead bromide (CsPbBr3) perovskite micro-hemispheres fabricated by chemical vapor deposition. A series of lasing property analysis based on cavity size was reported under this material system. Due to good optical confinement capability of the whispering gallery resonant cavity and high optical gain of CsPbBr3 perovskite micro-hemispheres, single-mode lasing behavior was achieved with an ultra-high quality factor as large as 11,460 at room temperature. To study in detail the physical effects between lasing threshold and cavity, a set of cavity size dependence photoluminescence analyses were performed. We found that the lasing threshold increases while the cavity size decreases. Time-resolved PL analysis was conducted to confirm the relation between cavity size and lasing threshold. The larger cavity stands for longer PL lifetime and indicates easier-to-achieve carrier population inversion. Strong Purcell enhancement could be further investigated by the spontaneous emission coupling factor β and internal quantum efficiency as a function of cavity size. A high β-factor of 0.37 could be obtained from a 2.2 μm diameter hemisphere microcavity and a high Purcell factor of 14 in a 1.9 μm diameter hemisphere microcavity showing strong Purcell enhancement effect in our system.

We report the CsPbI

We construct the ZnO-based superluminescent light-emitting diodes (SLEDs) by spin-coating ZnO nano-particles onto p-GaN/sapphire substrate. By inserting another thin Al layer to form an n-ZnO/Al/n-ZnO/p-GaN sandwich structured SLD, the intensities of the photoluminescence and electroluminescence were greatly enhanced, which can be attributed to the surface plasmon resonance of this Al layer. The tendency of the intensities of the entire electroluminescence spectra shows a super-linearly behavior with increasing the forward bias. Besides, the spectral bandwidth is narrowed down enormously owing to the achievement of the SLD. Furthermore, the interfacial emissions between ZnO/GaN are effectively suppressed by partially oxidizing the Al layer.

Large-grained and well-oriented methylammonium lead tribromide (MAPbBr3) perovskite was formed from the conversion of amorphous lead bromide (PbBr2) doped with phenethylamine (PEA). The addition of PEA ions (with an optimized molar ratio of 0.008%) to the PbBr2 solution assisted the formation of a smooth PEA-doped PbBr2 layer by spin-coating. Then, the PEA-doped PbBr2 thin film would convert into large-grained and well-oriented MAPbBr3 with the help of a solid-vapor reaction under a vaporized methylammonium bromide (MABr) and choline chloride (CC) atmosphere. Furthermore, both PEA and CC would passivate the defects of perovskite to improve the crystal quality of perovskite. By applying this perovskite layer in perovskite light-emitting diodes (PeLEDs), the maximum luminance and current efficiency of PeLEDs could reach 20,869 cd/m2 and 3.99 cd/A, respectively; these values are approximately five and three times larger than those of PeLEDs without PEA. The perovskite converted from spin-coated PbBr2 with a PEA dopant remarkably improved the luminance and current efficiency of its PeLEDs.

ZnO nanowires doped with Aluminium (AZO) grown by chemical bath deposition technique on ITO/glass substrates exhibit random lasing emission with lowest threshold of just 0.07 W/cm2 when 12.5 % of aluminium nitride was added during the growth of the nanorods. Compared to pure ZnO nanorods, grown with the same parameters, threshold was at least 2 orders of magnitude lower. Results overall indicate incorporating aluminium reduces threshold for random lasers however improvements in doping high aluminium content without affecting growth is required to reduce the threshold at high doping levels.

In this paper, we report SiO2 capped Zinc Oxide nanorod array (SiO2 capped-ZnO NAs) for enhancing UV random lasing emissions at room temperature. A simple method chemical bath deposition (CBD) under optimum conditions was used to from vertically aligned ZnO NAs on glass substrate at room temperature. The random lasing emission intensity increased 30 times compared to bare ZnO NAs (without SiO2) at the same pump power. The best sample with 100 nm of SiO2 capping showed superior lasing, whereby the random lasing peaks almost suppressed the spontaneous emission peak completely. This enhancement was attributed to improved light confinement inside the ZnO NAs resonators which increases the performance of the stimulated light emission within the gain medium. To further understand the mechanism behind the enhanced lasing properties, a numerical simulation using finite-element method was performed. The simulation results showed SiO2 capped-ZnO nanorod lead to an enhancement of light confinement within the resonators.

The random laser was investigated in gold-doped Zinc Oxide nanorods (Au-doped ZnO NRs) under a range of pumping power 0.25 - 4.66 mW. The Au-doped ZnO NRs prepared by chemical bath deposition (CBD) on the ZnO seed layer, were pre-coated on glass substrate using radio frequency magnetron sputtering (Rf-sputtering). The morphological of Au-doped ZnO NRs shows a hexagonal and strong vertically alignment against the substrate. The Energy dispersive spectroscopy (EDX) spectrum and elemental mapping results confirmed that Au atoms (at.%) are doped and spread over the ZnO NRs. More interestingly, the random laser of Au-doped ZnO shows a redshift of ~38 nm. This study showed the ability of using doping as a tuning parameter in the random laser, also provided an emphasis on Au-doped ZnO NRs as suitable options for controllable random laser devices.

Random lasing emission was investigated from different ZnO nanostructures: a transition from nanowalls to nanoflakes; prepared on seeded glass substrate using simple chemical bath deposition method. The transition geometry of ZnO nanostructures were achieved simply by tuning the equimolar concentration of the chemical bath solution, zinc nitrate hexahydrate, and hexamethylenetetramine from 0.15 M, 0.20 M to 0.25 M. This leads to the changes in particle size of nanostructures from 168.47 nm to 365.91 nm, and finally to 534.07 nm. The population decreased from 131 nanostructures to 100, and finally to 26 nanostructures based on a surface area of 2.8 µm × 2.5 µm, and accordingly enhanced crystallite size was observed as 90.21 nm, 98.04 nm to 110.79 nm for the nanowalls to nanoflakes respectively. These physical variations of the scattering medium affect random lasing emission threshold whereby the threshold excitation power density was reduced from 40 kW/cm2 to 17.14 kW/cm2, and finally to 14.29 kW/cm2 when the structure was in the form of nanoflakes. The emission wavelength from the structures shows a Stokes shift pattern and self-reliant while maintaining a stable emission at 379.7 nm (0.15 M), 382.7 nm (0.20 M), and 387.2 nm (0.25 M). This work demonstrates that by simply tuning the chemical bath solution molarities, changes in nanostructures from nanowalls to nanoflakes were obtained, and upon optical pumping, nanoflakes showed the lowest threshold for random lasing to occur indicating the best structure for ZnO random lasers.

Vertically aligned Al-doped ZnO nanorods (AZO-NRs) were grown on glass substrate using a chemical bath deposition (CBD) method at various temperatures between 80°C and 130°C. The results showed the Al content in the AZO-NRs strongly depends on the growth temperature. The optimum doping level was attained at 110°C. The morphology was maintained in each sample, and the lasing properties were investigated against the Al-doped variation. The sample with a high doping level exhibited superior random lasing, with high intensity and spectral width of less than 0.08 nm. The same sample also had the lowest pumping threshold of 0.192 mW. More importantly, this study showed the possibility of utilizing doping as a tuning parameter for random lasing, whereby a 7.3 nm redshift in the lasing peak was observed with increasing doping concentration. This study also placed an emphasis on AZO-NRs as potential candidates for tunable random laser devices.

In this paper, we report on room temperature UV lasing emission observed in a mirror-less ZnO sample prepared by two-step chemical bath deposition technique; a popular low cost method for making ZnO nanorods. We attribute the mechanism of the laser emission to coherent multiple light scattering between the nanorods within the illuminated area of excitation. Reduced threshold condition was observed for the nanorods having smallest crystallite size. Furthermore, the ability to maintain the number of modes at different excitation areas of the sample as well as at different pump powers suggests this method of growing the ZnO nanorods as a promising growth method for industry in developing high efficiency low cost random lasers for future integrated photonic devices.

We measure the optical model gain of single Zinc Oxide microrod by Variable Stripe Length method. The pick value of gain spectra in room temperature is well below the bandgap of bulk ZnO, which comes from exciton-exciton scattering, and it can be as a reference for the design of UV-devices.

We report the influence of Mn dopant on magnetic properties of Zn

Time-resolved X-ray excited optical luminescence (TR-XEOL) was developed successfully for the 23A X-ray nanoprobe beamline located at the Taiwan Photon Source (TPS). The advantages of the TR-XEOL facility include (i) a nano-focused X-ray beam (

We propose “the external reflectance versus height conversion (ERHC) method” for measuring the full-field three-dimensional surface topography of a sample height from one micron to 100 micrometers. It is similar to the camera method, capturing images reflected and/or not from a prism by using a lens and a CCD. The reflectance of a point in the image can be converted to the height of the point. The method can obtain large-area full-field real-time three-dimensional measurement results and has the advantages of simple operation, low cost, and easy assembly. The measurement area is in the range of a few square millimeters for each time. The lateral and vertical resolutions are 2 and 0.1 micrometers, respectively, and the error is about 1% compared with the confocal microscope.

Random lasing was demonstrated from aluminum doped ZnO nanorods fabricated on ITO coated glass substrates using simple chemical deposition technique. Different Aluminum (Al) doping parameters were explored in an attempt to realize low threshold ZnO random lasers. Results confirm threshold was strongly dependent on doping concentration and suggestive of resonant coupling with Al in lowering the threshold by 2 orders of magnitude when compared to undoped ZnO nanorods. Lowest threshold was obtained from ZnO nanorods doped with 10 mM of aluminum, suggesting best doping concentration for ZnO random lasers formed by nanorod array. Results further indicate possibility of controlling random lasing properties by adjusting the doping concentration.

We study Raman spectra of ZnO nanoparticles of 5–12 nm size in the whole range of the first-order phonon bands. We apply the 3D phonon confinement model (PCM) for the interpretation of the observed Raman spectra. It is found that PCM is well applicable to the acoustic modes as well as to the optical ones, despite the fact that PCM has been thought not to be suitable for acoustic phonons. We show that the asymptotic behavior of PCM for the small-size limit is more consistent with the observation than that of the elastic sphere model (ESM). Furthermore, PCM gives detailed information on the complex size-dependent shapes of the phonon bands.

The multifunctional hard X-ray nanoprobe at Taiwan Photon Source (TPS) exhibits the excellent ability to simultaneously characterize the X-ray absorption, X-ray excited optical luminescence (XEOL) as well as the dynamics of XEOL of materials. Combining the scanning electron microscope (SEM) into the TPS 23A end-station, we can easily and quickly measure the optical properties to map out the morphology of a ZnO microrod. A special phenomenon has been observed that the oscillations in the XEOL associated with the confinement of the optical photons in the single ZnO microrod shows dramatical increase while the X-ray excitation energy is set across the Zn K-edge. Besides having the nano-scale spatial resolution, the synchrotron source also gives a good temporal domain measurement to investigate the luminescence dynamic process. The decay lifetimes of different emission wavelengths and can be simultaneously obtained from the streak image. Besides, SEM can provide the cathodoluminescence (CL) to be a complementary method to analyze the emission properties of materials, we anticipate that the X-ray nanoprobe will open new avenues with great characterization ability for developing nano/microsized optoelectronic devices.

Single-crystal all-inorganic CsPbBr3 perovskite microplatelets were fabricated to realize lasing at room temperature. Upon optical excitation, whispering-gallery-mode (WGM) lasing was achieved at RT with low threshold (~2.8 μW) and high quality factor (~3000).

Selective-area growth (SAG) of single-crystal wurtzite GaN nanorods (NRs) directly onto Si(001) substrates with un-etched native SiOx amorphous layer, assisted by a patterning TiNx mask fabricated by nanosphere lithography (NSL), has been realized by reactive magnetron sputter epitaxy (MSE). The GaN NRs were grown vertically to the substrate surface with the growth direction along c-axis in the well-defined nano-opening areas. A 5-step structural and morphological evolution of the SAG NRs observed at different sputtering times depicts a comprehensive growth model, listed in sequence as: formation of a polycrystalline wetting layer, predominating c-axis oriented nucleation, coarsening and coalescence of multi-islands, single NR evolution, and finally quasi-equilibrium crystal shape formation. Room-temperature cathodoluminescence spectroscopy shows a strong GaN bandedge emission with a uniform luminescence across the NRs, indicating that the SAG NRs are grown with high quality and purity. In addition, single-longitudinal-mode lasing, attributed to well-faceted NR geometry forming a Fabry–Pérot cavity, was achieved by optical pumping, paving a way for fabricating high-performance laser optoelectronics using MSE.

We report the influence of Mn dopant on magnetic properties of Zn0.95Mn0.05O (ZMO)/Al2O3(0 0 0 1) hetero-epitaxial systems grown by using pulsed-laser deposition. The room temperature (RT) intrinsic ferromagnetic (FM) ordering verified by superconducting quantum interference device magnetometer and x-ray magnetic circular dichroism spectrum of Mn L 2,3 edges is ascribed to the substitutional Mn atoms in the Zn site of ZnO. Mn in ZMO has a tetrahedral local symmetry instead of the octahedral symmetry of MnO, after verifying the absence of the Mn-related impurities or clusters in ZMO epitaxial film by Mn K-edge and Zn K-edge x-ray absorption spectroscopy spectrum, as well as the analysis of long-range structural ordering on Renninger scan of forbidden (0 0 0 5) reflection in x-ray diffraction, transmission electron microscopy and Raman spectrum. Comparison of x-ray absorption spectra of ZMO with those of ZnO epilayers at O K-, Zn K-, and L 3-edges indicates that the substitution of the Zn site with Mn enhances the charge-transfer (CT) transition and the presence of Zn vacancies (VZn) also dominate the photoluminescence (PL) spectrum, implying that the formation of numerous VZn defects plays an important role in activating FM interactions. The strong CT effect and the existence of high-density VZn suggest that the intrinsic RT FM ordering of insulating ZMO is a result of the formation of the bound magnetic polarons (BMPs) that interact with each other via intermediate magnetic impurities.

CH3NH3PbI3 perovskite material has demonstrated great promise in high-performance solar cells and light-emitting devices (LEDs). In this work, we investigated the impact of the coexistence of PbI2 and CH3NH3PbI3 perovskite on photoluminescence (PL) properties. In absorbance and PL measurements performed at room temperature, we observed an emission peak at 780 nm, which is consistent with the band-edge absorption of CH3NH3PbI3. On the top surface, we observed dissolved PbI2, which could serve as a passivation species for improving PL stability upon exposure to ambient conditions. Specifically, dual-peak PL spectra were observed at room temperature. The peak at 780 nm originates from the free-carrier transition of CH3NH3PbI3 and the peak at 796 nm originates from the PbI2-related recombination. Based on time-resolved PL and X-ray diffraction measurements, we can conclude that unconverted and dissolved PbI2 in CH3NH3PbI3 forms a type-II band alignment at the CH3NH3PbI3/PbI2 interface. This type II hetero-structure indeed influences the quality and PL performance of perovskites. To check this structure or quality of perovskite, x-ray diffraction (XRD) and x-ray photoemission spectroscopy (XPS) are common ways. Here, we demonstrated a cheaper, faster and more convenience method, PL measurement, to check the quality of CH3NH3PbI3 perovskite films. It should be a useful way to check the quality perovskite-based LEDs and solar cells merely by observing whether the dual peaks exist or not in the PL spectra.

Taijiang National Park, established at the end of 2009, brought about a structural change from a top down to a bottom up policy process and marked a turning point in the establishment of national parks in Taiwan. This paper used a political ecology perspective and analytical matrices of stakeholders to discuss the creation of Taijiang National Park, and also attempted to establish an assessment structure and indicators to assess whether Taijiang National Park has gradually become a provider of “benefits beyond boundaries” or not? Finally, the authors identified that involving the local community to integrate Taijiang's ecotourism with local values should be Taijiang National Park Headquarters' main strategy and primary responsibility for future sustainable development of ecotourism.