The local structure of europium doped and impregnated ZrO 2 in the amorphous state and during crystallization is investigated by in situ X-ray diffraction and in situ Raman, high-resolution transmission electron microscopy (HRTEM) and time-resolved photoluminescence spectroscopy. From Raman spectra excited at three different wavelengths (λ ex = 488, 514, and 633 nm), both phonon modes of ZrO 2 and photoluminescence (PL) corresponding to europium electronic transitions were investigated. In the assynthetized state, samples were X-ray and Raman amorphous with few tetragonal (also monoclinic) crystallites being observed under HRTEM microscopy. In situ XRD patterns show that all samples crystallize in the tetragonal phase around 450 °C. The time-resolved PL spectra of europium doped and impregnated ZrO 2 show spectral dynamics with time delay after lamp/laser pulse which is assigned to the coexistence of the different amorphous and crystalline components or unreacted europium precursor. From in situ Raman spectra, crystallization was detected at 300−350 °C, monitoring for the characteristic tetragonal-like 5 D 0 − 7 F 2 emission of europium at 606 nm. The ratio of tetragonal to amorphous emission increased abruptly from ca. 2−4% at 300−400 °C to almost 25% at 400−450 °C, whereas at 500 °C the emission is mostly tetragonal. A similar trend was found with the ex situ calcined samples, but relative strong tetragonal emission was observed at lower temperature in the range of 350 to 400 °C.
Crystalline ZnO and ZnO 2 nanoparticles (NPs) were prepared in one-pot oil-in-water (O/W) microemulsion media at room temperature by adding an aqueous solution of sodium hydroxide (followed by H 2 O 2 in the case of synthesis of ZnO 2 ) to the O/W microemulsion containing a Zn(II) organometallic precursor dissolved in the oil phase. After calcination of ZnO 2 NPs, ZnO NPs were also obtained, and their characteristics were compared with those of ZnO NPs prepared directly in O/W microemulsion. The materials were characterized by X-ray diffraction, scanning electron microscopy, and high-resolution transmission electron microscopy. Nanostructured ZnO materials have attracted a lot of attention in recent years because of their optical, electrical, and chemical properties, as well as their low toxicity. These materials are n-type semiconductors with a band gap of 3.37 eV and an exciton binding energy of 60 meV; in addition, they exhibit efficient UV-stimulated emission 1 at room temperature. Nanostructured ZnO has great potential for use in a wide range of applications, for example, in phosphors, 2,3 varistors, 4a,4b gas sensors, 57 UV absorbers, 8 and antimicrobial agents, 9 and more recently, in solar cells.
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