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We demonstrate that the upconversion nanoparticles (UCNPs) fluoresce 50 times more on a gold (Au) coated Cicada wing. UCNPs are attractive bioimaging, and therapeutic materials as it is excited in the infrared, limited only by the low fluorescence quantum yield. Here, a plasmonic effect, coupled with an anti-reflecting (AR) Cicada wing substrate coated with Au is demonstrated to enhance the fluorescence of the UCNPs. Silica (SiO2) coated Erbium doped green emitting core-shell UCNPs (NaYF4: Yb3+, Er3+@SiO2) show conventional metal enhanced fluorescence. The AR property of the Cicada wing (R ~0.2% @ 1000 nm) contributes >6-fold enhancement as compared to flat (silicon, and quartz) substrates (R~10–30% @ 1000 nm). Upon plasmon coupling, with an optimally sputtered Au coating, an unprecedented enhancement of >50-fold for the 520, and 655 nm emission was obtained on the Au coated Cicada wings, vis-a-vis planar uncoated (silicon, and quartz) substrates. The enhancement was also confirmed by direct fluorescence imaging of the photonic substrates used. The fluorescence lifetime of the core, and the core-shell UCNPs (~300 μs) decreased by ~30–40%, and 10–30%, respectively, when placed on Au coated substrates.

We report electrostatically conjugated core- silica (SiO2) shell upconversion nanoparticle (UCNPs@SiO2), and gold nanorod (AuNR) nanocomposite (NC) combined with graphene to demonstrate > 200-fold UC fluorescence enhancement. Plasmonic AuNR and graphene, resulted in enhanced fluorescence in UCNP with a maximum for the SiO2 shell thickness of 7 nm supported by finite difference time domain simulation of electric field distribution. In addition to the conventionally reported spectroscopic evidence, the plasmon aided UC fluorescence enhancement was demonstrated by direct confocal fluorescence imaging also, which was corroborated by a ~40% decrease in fluorescence lifetime. Finally, we have fabricated a NC/graphene hybrid photodetector (PD) that showed broadband (455–980 nm) photoresponse, with photoresponsivity of ~5000 AW−1, and response times of 80–200 ms under 980 nm illumination. The multiphoton infrared (IR, ~980 nm) absorbing UCNPs also show interesting high energy (blue (B), green (G), and red (R)) photoresponse which is now conclusively attributed to one-photon absorption in the UCNPs. We report, probably for the first time, the performance of the hybrid PD under monochromatic and polychromatic illumination of B, G, R, B + G, B + R, G + R, and B + G + R, among others. The photocurrent under polychromatic conditions is dominated by the strongest monochromatic response, and does not scale with net power of the illumination. The loss in photocurrent is attributed to saturation in absorption, and photothermal heating. The fast response of the PD device has been demonstrated while detecting high frequency modulated AC remote controller signals, and attributed to the fast charge sweeping by the AuNRs.

Photolithography has been widely implemented with a photomask in contact or in close proximity to the photoresist layer. The flatness of the substrates is a crucial factor to guarantee the quality of the entire patterned photoresist (PR) layer especially for large-area photolithography. However, some substrates, such as sapphire wafers, do not possess highly uniform thickness as silicon wafer does. In this work, we demonstrate that a flexible polydimethylsiloxane (PDMS) photomask with optical total-internal-reflection structure can effectively circumvent this problem for mass production. Different from conventional photomask that the light is blocked by the patterned reflective/absorbing materials, the distributions of light intensity on the PR is engineered by the geometric structure of the transparent PDMS photomask. We demonstrate that 4 in. patterned sapphire wafers can be successfully fabricated by using this PDMS photomask, which can be easily integrated into the present techniques in industry for mass production of substrates for GaN-based optoelectronic devices.

The nanopatterned c -plane sapphire substrate with different morphologies can be successfully used to grow polar and nonpolar GaN epilayers. The nanopattern of sapphire substrate was prepared with natural lithography and dry-etching methods and the following GaN epilayer was grown by MOCVD. The GaN crystal orientation and crystalline quality were then characterized by high resolution X-ray diffraction, which reveals the GaN epilayer can be c -plane (0001) or m -plane (1010) orientation depending on the surface morphology of nanopatterned sapphire substrate. The corresponding full width at half maximum of the rocking curves for c - and m -plane GaN are 211 and 316 arcsec, respectively. The rms surface roughness was measured to be 0.3 nm by atomic force microscopy. The atomic structure of the sapphire-GaN heterointerface was studied by high resolution transmission electron microscope to reveal the growth mechanism. Furthermore, photoluminescence, time-resolved photoluminescence, and polarization Raman spectroscopy were employed to realize the optical and structural properties of these GaN epilayers.

Nonpolar ( 10 1 ¯ 0 ) m-plane GaN epilayer was grown on nanoscale patterned c-plane sapphire substrates by MOCVD. The nanoscale patterned sapphire substrates were fabricated by natural lithography and dry etching methods. The nanopatterns are defined particularly with no c-plane surfaces exposed. The ( 10 1 ¯ 0 ) m-plane GaN epilayer was characterized by X-ray diffraction and atomic force microscope, which indicated the FWHM of the rocking curve is 316 arcsec and the rms surface roughness is 0.3 nm, respectively. The SEM and TEM studies reveal that the m-plane GaN grains nucleate on the exposed n-plane facets of the etched c-plane sapphire substrates.

The use of a horn sonicator (Misonix, 20 kHz) to recover the flux in the ultrafiltration (UF) of suspended solutions was studied. Two types of solutions, i.e., the Cu2+–polyethylenimine (PEI) solution and the W/O emulsions dispersed in aqueous solution, were selected, which were widely found in binding-UF and liquid surfactant membrane (LSM) processes, respectively, for removal of toxic heavy metals from effluents. The Amicon YM10 membrane (regenerated cellulose, MWCO 10,000) was used. Experiments were performed as a function of tip position, ultrasonic power, and solution properties such as target ion concentration, percentage of emulsification, and volume ratio of W/O emulsions to the external aqueous phase. It was shown that ultrasound associated with a hydraulic pressure of 10 psi was a promising method for the recovery of UF flux, particularly for the solution with less fouling potential. Careful control of the ultrasonic intensity could keep the membranes durable and prevent the organic compounds (PEI in the Cu2+–PEI solution; carrier, surfactant, and solvent in the W/O/W solution) from degradation. Finally, the fouling of membrane during UF of W/O/W solutions was analyzed by the resistance-in-series model.

Liquid surfactant membrane (LSM) process is a novel and effective method for the recovery and separation of heavy metals and amino acids from aqueous solutions. Repeated production and destruction of W/O emulsions plays a crucial role in the LSM process. The aim of this work was to study the efficiency of emulsification with horn ultrasound (20 kHz), in which the organic phase contained the surfactant Span 80 and the acidic carrier di(2-ethylhexyl)phosphoric acid (D2EHPA) in kerosene. The (internal) aqueous phase consisted of divalent Cu(II)-EDTA chelated anions as the tracers. All experiments were performed as a function of emulsification time, surfactant and carrier concentrations, ultrasonic power, and volume ratio of the internal aqueous phase to organic phase. It was shown that in most cases the emulsification was finished with 1 min. With ultrasound, the droplet sizes of W/O emulsions (Sauter diameter, d32) were much smaller than those reported previously by mechanical agitation. The effect of ultrasonic power and surfactant concentration on the droplet size was also investigated. Finally, the possibility of ultrasound demulsification was evaluated and discussed.