ZnO is a unique material that offers about a dozen different application possibilities. In spite of the fact that the ZnO lattice is amenable to metal ion doping (3d and 4f), the physics of doping in ZnO is not completely understood. This paper presents a review of previous research works on ZnO and also highlights results of our research activities on ZnO. The review pertains to the work on Al and Mg doping for conductivity and band gap tuning in ZnO followed by a report on transition metal (TM) ion doped ZnO. This review also highlights the work on the transport and optical studies of TM ion doped ZnO, nanostructured growth (ZnO polycrystalline and thin films) by different methods and the formation of unique nano- and microstructures obtained by pulsed laser deposition and chemical methods. This is followed by results on ZnO encapsulated Fe3O4 nanoparticles that show promising trends suitable for various applications. We have also reviewed the non-linear characteristic studies of ZnO based heterostructures followed by an analysis on the work carried out on ZnO based phosphors, which include mainly the nanocrystalline ZnO encapsulated SiO2, a new class of phosphor that is suitable for white light emission.
Reaction of Sn(IV) with phosphonic acids results in the formation of tin phosphonates with a spherical morphology arising from the aggregation of nanosized individual particles. Under high magnification, the spheres are shown to be porous with surface areas of 200-515 m2/g, depending on the type of phosphonic acid and the synthesis conditions used. The pores are largely micro in nature but also somewhat dependent on the type of phosphonic acid utilized in the preparation. Both aliphatic and aromatic organic phosphonates form these spherical aggregates. Functional groups, such as amino and carboxyl, may be introduced as part of the phosphonic acid or subsequently by further reaction, leading to a large family of naturally formed nanoparticles with accompanying microporosity.
A bright red colour emitting Mn doped Ba2ZnS3 phosphor was prepared by an ecologically acceptable carbothermal reduction method without an inert gas or hazardous gas (H2S) environment. The phosphor can be excited with UV wavelength radiation to realize emission in the visible range. X-ray diffraction studies confirm an orthorhombic structure with phase group, pnam. The photoluminescence (PL) emission spectrum shows a broad band with emission maximum at 625 nm under the host excitation of 358 nm, which lies in the near UV region. The concentration of Mn was varied from 0.0025 to 0.20 mole with respect to Zn and the optimum PL emission intensity was obtained at the concentration of 0.01 mole of Mn. The CIE (Commission Internationale de l'Eclairage) colour coordinates measurement (x = 0.654 and y = 0.321) shows that the primary emission is in the red region. The triband phosphors blend containing Sr5(PO4)3Cl : Eu2+ (blue), ZnS : Cu,Al (green) and Ba2ZnS3 : Mn (red) shows white light emission under 365 nm excitation having CIE chromaticity (x = 0.292 and y = 0.251). Since phosphor excitation lies in the near UV excitable region, giving a bright red emission, it can be used for applications in near UV phosphor converted white LED lighting and display devices.
A bright green light emitting Zn 2 SiO 4 :Mn phosphor has been prepared at low temperature 800°C through gel combustion synthesis using zinc nitrate, manganese acetate, urea in a silica gel matrix. The structure and morphology of the phosphors using scanning electron microscopy along with thermogravimetric analysis/differential thermal analysis/Fourier transform infrared study along with X-ray diffraction, diffuse reflectance spectroscopy, and photoluminescence ͑PL͒ data show interesting trends with respect to the phase evaluation of Zn 2 SiO 4 :Mn phosphor. Photoluminescent and crystalline properties are examined as a function of firing temperature and Mn concentration. Maximum PL intensity is observed at em = 522 nm for 0.03 Mn 2+ concentration, which can be attributed to the 4 T 1 ͑G͒ − 6 A 1 ͑S͒ transition of Mn 2+ under short ultraviolet excitation. The PL emission intensity of these phosphors is found to be more superior to that of the corresponding samples prepared using the conventional solid state method implying the suitability of this route for the preparation of device worthy phosphor materials.
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