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The effect of different light wavelengths on methylene blue dye doped poly(methyl methacrylate) thin films during casting was investigated. The colour of the thin films which casted under the light sources of short wavelength ultraviolet light (254 nm), long wavelength ultraviolet light (367 nm) and sunlight were compared with the film casted in the dark. UV–vis spectrometer was used to measure the transmittance and absorbance of the fabricated films, and moreover, band gap energies were calculated. Results show that the wavelength of the applied light influences on the colour stability of methylene blue due to the photolysis of poly methyl methacrylate or chloroform (solvent). The highest decolourization rate was observed under the illumination of 254 nm, in which 90% of the colour was discharged after 30 min of illumination's time. However, no colour change was observed when the thin films were kept in dark during the casting step. [ABSTRACT FROM AUTHOR]

A p-ZnTe/n-CdSe heterojunction was used for making polycrystalline ZnTebased UV sensors. The heteropair components have the same crystal structure and close lattice parameters. ZnTe and CdSe were grown using thermal evaporation and quasiclosed space condensation. A transparent current collecting electrode for the surfacebarrier structure of p-ZnTe/n-CdSe heterojunction was made of degenerate p-Cu1.8S. Surface relief of ZnTe grown on different substrates was studied with scanning atomic force microscopy. The energy band offset diagrams of heterojunction are built and photosensitivity spectra are presented. [ABSTRACT FROM AUTHOR]

The Eu(DBM) 3 Phen complex has been synthesized and dispersed in poly(methyl methacrylate) and polyvinyl alcohol matrices in order to explore its versatile applicability. Excitation spectroscopy monitored at 611 nm show intense ultraviolet-blue spectra (∼250 to 450 nm) pointing to efficient energy transfer from the organic ligands to the central Eu 3+ ion. The excellent photoluminescence properties, i.e., broad-band excitation spectra, sharp and intense emission, and long lifetime open the door for appealing multi-applications such as temperature sensing, ultraviolet light detection, and laser applications. Photoluminescence based temperature sensing with a sensitivity of up to 1.75% per K is demonstrated for the temperature range of 50–318 K, and additionally, ultraviolet radiation detection is demonstrated, whilst impinging ultraviolet intensities as weak as 96 nW/cm 2 can be detected. The work further reports several essential device characteristics, such as emission dependence on impinging excitation intensity, sensor stability, and photoluminescence response times. Finally, by increasing the optical excitation, amplification in spontaneous emission and decrease of full width at half maximum take place, pointing to stimulated emission. This feature, in conjunction with the stimulated emission cross-section of 3.24 × 10 −20 cm 2 , which is comparable to the Nd-Glass laser, suggests the suitability of the investigated lanthanide-polymer merger for laser realizations. [ABSTRACT FROM AUTHOR]

Abstract: Novel nanostructured thin-film arrays of nanohole-enhanced aligned aluminium (Al)-doped zinc oxide (ZnO) nanorods were prepared using sonicated sol–gel and immersion methods for metal–semiconductor–metal (MSM)-type ultraviolet (UV) photoconductive sensor applications. These nanorod arrays were grown on a glass substrate coated with ZnO nanoparticle thin film as a seed layer at immersion times ranging from 10 to 120min. Notably, the nanoholes appeared on the nanorods after the annealing process due to the evaporation of water and impurities. The photocurrent properties for the Al-doped ZnO nanorod arrays were significantly improved, increasing by more than five-fold compared to the seed layer when the sensor was illuminated with 365nm UV light at a density of 750μA/cm2. Interestingly, the highest responsivity using the Al-doped ZnO nanorod arrays was 1350.84A/W with an improved photocurrent-to-dark current ratio of 22.7, achieved for the samples prepared with a 50min immersion time and a gap between metal contacts of 0.07mm. Our results show that high-performance UV photoconductive sensors can be achieved using a novel structure of nanohole-enhanced aligned Al-doped ZnO nanorod arrays prepared at low immersion times which reduces fabrication time and cost. [Copyright &y& Elsevier]

Highlights: [•] First time growth of high quality, ultra long SnO2 nanowires on black silicon. [•] UV and visible light detection at room temperature. [•] Fast response under 1s and recovery around 10s at room temperature. [•] Response of 92% for 320–400nm UV at 2.7mW/cm2. [ABSTRACT FROM AUTHOR]

Highlights: [•] Hybrid structures composed of 1D ZnO and 2D NiO nanosheets were demonstrated. [•] The decrease of the trap-state emission and recombination of excitons was observed. [•] The hybrid structures showed over ten folds improved UV sensitivity due to the synergetic effects. [Copyright &y& Elsevier]

Abstract: Ultra-long and flexible single-crystalline lead zirconate titanate Pb(Zr0.52Ti0.48)O3 (PZT) nano/micro-wires (N/MWs) were synthesized via a hydrothermal method. Owing to the self-polarization effect of the as-synthesized PZT N/MWs, the N/MWs can be used to directly fabricate a nanogenerator (NG) without being poled under electric field. Using such an NG, we demonstrated a flexible, self-powered system for detecting UV irradiance by utilizing the cycled contraction-expansion of a flexible rubber membrane. [Copyright &y& Elsevier]

Abstract: This paper describes the characteristics of surface acoustic wave (SAW) ultraviolet (UV) sensors fabricated from a ZnO thin film using the third harmonic mode. A ZnO thin film was used as an active layer for UV detection, and a piezoelectric layer was sputtered using magnetron sputtering. The X-ray diffraction (XRD) and photoluminescence (PL) spectra showed that the ZnO sputtered onto Si(100) was highly (002)-oriented and had good optical properties. The two-port SAW resonator was based on an inter-digital transducer (IDT)/ZnO/Si structure and was fabricated and exposed under UV light at a wavelength of 380 nm. As a result, under a UV intensity of 3 mW/cm2, the SAW UV sensor was greatly shifted by 400 kHz at the third harmonic mode compared to a frequency shift of 10 kHz in the fundamental mode. [Copyright &y& Elsevier]

Abstract: Highly oriented TiO2 nanorod arrays were fabricated directly on fluorine-doped tin oxide-coated glass (FTO) substrate by the hydrothermal method. The diameter, length, and density of the nanorods could be varied by changing the growth parameters, such as time, temperature, and initial reactant concentration. The fabricated samples were characterized with X-ray diffraction, field-emission-scanning electron microscopy, transmission electron microscopy, high resolution transmission electron microscopy and energy dispersive X-ray spectroscopy. The TiO2 nanorod array was applied to construct photoelectric devices, by which highly sensitive and steady photocurrent responses were obtained. [Copyright &y& Elsevier]

Abstract: Transferable ZnO tetrapods were grown by an aqueous solution method. An individual ZnO tetrapod-based sensor was fabricated by in situ lift-out technique and its ultraviolet (UV) and gas sensing properties were investigated. This single tetrapod-based device responds to the UV light rapidly and showed a recovery time of about 23s. The sensitivity of a single ZnO tetrapod sensor to oxygen concentration was also investigated. We found that when UV illumination is switched off, the oxygen chemisorption process will dominate and assists photoconductivity relaxation. Thus relaxation dynamics is strongly affected by the ambient O2 partial pressure as described. We also studied the response of ZnO tetrapod-based sensor in various gas environments, such as 100ppm H2, CO, i-butane, CH4, CO2, and SO2 at room temperature. It is noted that ZnO tetrapod sensor is much more sensitive to H2, i-butane and CO. It is demonstrated that a ZnO tetrapod exposed to both UV light and hydrogen can provide a unique integrated multiterminal architecture for novel electronic device configurations. [Copyright &y& Elsevier]

Nanosized TiO2 thin films were deposited by conventional vacuum thermal evaporation and triode-cathode sputtering of Ti on silicon and quartz substrates. To form TiO2 a high temperature annealing of the Ti films was carried out in the range of 450÷800 °C. The optical properties of TiO2 were studied by measuring UV-VIS transmittance spectra and the indirect band gap was evaluated. Scanning electron microscope (SEM), atomic force microscope (AFM) and energy-dispersive spectroscopy were employed for surface and structure analysis. Structures for UV sensors were formed by thermal evaporation of various combing contacts on the TiO2/Si substrates. The photoresponse of the structures was detected in the wavelength range of 235÷420 nm. An increase in photocurrent with an order of magnitude was detected by exposing samples to UVA illumination and applying 6÷10 V bias voltage. The obtained results indicated that the studied structures are suitable for UV sensors. [ABSTRACT FROM AUTHOR]

Abstract: In this paper we present an improved structure of an amorphous silicon/amorphous silicon carbide ultraviolet sensor, previously presented in literature, whose overall performances have been enhanced by growing a very thin layer of chromium silicide film on the top of the sensor. The sensor is a n-type amorphous silicon/intrinsic amorphous silicon/p-type amorphous silicon carbide stacked structure deposited on a glass substrate. The substrate is covered with a chromium film that acts as back metal contact. The top metal contact is a grid shaped chromium/aluminum/chromium metal stack that allows the incident radiation to reach the active p-type layer. The responses of two sets of sensors fabricated with and without the alloy film under ultraviolet radiation have been studied. The role of the very thin chromium silicide layer is to increase the conductivity of the top surface without attenuating the UV radiation absorbed in the device active layer. The increased top-surface conductivity ensures a better collection of the photogenerated carriers and hides the resistivity variation of the underlying p-doped layer under ultraviolet light caused by dopant activation, leading to a stable and linear behavior. Comparing the photocurrent values obtained on sensors with different area and distance between the grid electrodes, we found that the presence of the chromium silicide film extends the charge collection length by a factor of 10, allowing a better device photoresponse. [Copyright &y& Elsevier]

Abstract: A fiber-optic UV sensor based on azobenzene dye-doped polycarbonate film coated on a side-polished single mode fiber is proposed and demonstrated. The change of the refractive index of the film by exposure to UV results in a shift of the resonance wavelength in the device. The repeatable operation of the sensor is verified. The sensitivity, which is the shift of resonance wavelength per unit UV power density, is measured to be 2.35nm/(mW/cm2). The response time of the sensor is shown to be 26s. [Copyright &y& Elsevier]

Abstract: The characteristics of a 6H–SiC UV SENSOR with n+–p junction fabricated by N+-implantation, were investigated at high temperatures of up to 500 °C. Photocurrent was measured as a function of the incident light wavelength and the temperature of the sensor. The photocurrent was increasing with temperature elevation to be two to three times its room temperature value at 500 °C. The temperature coefficient of photocurrent was estimated to be about 0.5%/°C in the range of 100–500 °C at 250–300 nm. [Copyright &y& Elsevier]

We presented an ultraviolet (UV)-sensitive photofunctional device using a principle of evanescent field coupling occurring between SU-8 waveguide and photochromic dye (spirooxazine). The feasibility as a UV sensor was evaluated. When the 5-mm sensing area was irradiated with UV for 3 s, the absorption and the output intensity of the UV sensor was 0.0396 ∼ 0.114 absorbance/mW and 1 ∼ 10 mW, respectively. The UV sensor had linearity by variation of sensing area. The sensitivity of the proposed sensor was higher than the spectrophotometers method and optical fiber sensors. [ABSTRACT FROM PUBLISHER]