A layer-by-layer deposition of two conducting polymers, each layer of which is a few tenths of nanometer thick, has been successfully performed to enhance the thermoelectric power factor of organic thin films.
The effect of Mg incorporation on structural and optical characteristics of rhombohedral Zn 2 GeO 4 doped with manganese was systematically studied, fixing the concentration of manganese at 2 atom %. The phosphors were prepared by a high-temperature solid-state-reaction technique. The structural properties were studied using X-ray diffraction ͑XRD͒ and optical properties were characterized by diffuse reflectance spectra ͑DRS͒, photoluminescent excitation ͑PLE͒, and photoluminescent ͑PL͒ emission spectra. The XRD and DRS analyses reveal that Mg can be successfully alloyed in Zn 1.96−1.96x Mg 1.96x GeO 4 :Mn 0.04 up to x = 0.30 and forms a solid solution. The PL emission was maximum when 5 atom % Zn was replaced with Mg in comparison to an Mg-free Zn 1.96 GeO 4 :Mn 0.04 sample. The mechanism of luminescence is identified as resonant transfer from a subbandgap state in the host to Mn 2+ . The PLE and DRS spectra of Zn 1.96−1.96x Mg 1.96x GeO 4 :Mn 0.04 ͑0 ഛ x ഛ 0.5͒ exhibited a blue shift with an increase in Mg concentration. The cell volume was found to be a monotonously increasing function of Mg concentration up to x = 0.25, beyond which it varied randomly.
Phosphor-converted white light-emitting diodes (pc-WLEDs) are excellent energy-efficient light sources for artificial lighting applications. One goal of artificial lighting is to make objects/images look natural – as they look under the sunlight. The ability of a light source to accurately render the natural color of an object is gauged by the parameter – color rendering index (CRI). A conventional pc-WLED has an average CRI ~ 80, which is very low for accurate color reproduction. To utilize the pc-WLEDs for artificial lighting applications, all the CRI points (R1 – R15) should be above 95. However, there is a trade-off between CRI and luminous efficacy (LER), and it is challenging to increase both CRI and LER. Herein we propose a novel LED package (PKG) design to achieve CRI points ≥95 and efficiency ~100 lm/W by introducing two blue LEDs and a UV LED in combination with green and red phosphors. The silicone encapsulant, the current through the LEDs, and the green/red phosphor ratio were optimized for achieving high CRI and LER. Our re-designed LED PKG will find applications in stadium lighting as well as for ultra-high-definition television production where high CRI points are required for the artificial light source.
Multilayer structures of graphene oxide‐zinc oxide nanorods (GO‐ZnONRs) hybrids are successfully grown for use as an active material in resistive switching random access memory (RRAM) devices. A considerable reduction in the OFF current is achieved through a layer‐by‐layer growth of GO‐ZnONR multilayers up to three repeating layers as the active material. The scanning electron microscope images and X‐ray diffraction patterns of the hybrid multilayer structures reveal that vertically oriented ZnONRs are sandwiched between GO sheets. A Raman analysis shows that the G peak position in GO redshifts, due to the COZn bonding at interfaces of the hybrid multilayer structures. X‐ray photoelectron spectroscopy analysis of the hybrid multilayer structures also confirms the growth of GO on ZnONRs and secondary ZnONRs on GO, through a COZn bonding. This study realizes the growth of vertically oriented secondary and tertiary ZnONRs on GO, accompanying a tuning of photoluminescent emission wavelength. This hybrid multilayer structure‐based resistive memory device exhibits a stable resistive switching behavior with an ON–OFF ratio up to 3.3 × 105, which is higher by three orders of magnitude than the ON–OFF ratio of a single‐layer ZnONRs based device.
Bismuth telluride (Bi2Te3) and poly(3,4‐ethylenedioxythiophene) doped with poly(styrene sulfonate) (PEDOT:PSS) are two major inorganic and organic thermoelectric (TE) materials that are widely investigated for TE device applications. An inorganic–organic composite, based on Bi2Te3 and PEDOT:PSS possessing a high TE figure of merit, has immense potential in fabricating highly efficient and flexible TE generators. In order to achieve an enhanced TE performance, the interdependent TE parameters such as electrical conductivity and Seebeck coefficient of the composite should be decoupled. In this study, the TE properties of the composites are enhanced through the creation of additional defects in Bi2Te3 via proton irradiation. The structural variations occurred in Bi2Te3 via proton irradiation are analyzed using X‐ray diffraction, X‐ray photoelectron spectroscopy, and transmission electron microscopy, which quantitatively reveal structural damages as well as deviations from the Bi2Te3 stoichiometry. The proton irradiation‐induced antisite defects in the Bi2Te3 crystal are found to be beneficial in decoupling the interdependent TE parameters of Bi2Te3/PEDOT:PSS composite thin films, through which enhanced TE performance is achieved. The findings demonstrate that proton irradiation of Bi2Te3 is an effective method to engineer the TE properties through inducing defects in Bi2Te3 and enhancing the interaction between Bi2Te3 and PEDOT:PSS.
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