Synthesis and optical properties of ZnO and ZnO/PEO nanonsructured powders

Abstract

In this paper, microwave processing of nanostructured ZnO powder as well as preparation of nanostructured ZnO/PEO composite were described. As a fast processing method which introduces a large amount of energy in the reaction system, the role of microwave processing was to modify ZnO crystal structure, while the role of PEO was to additionally sensitivize surface of ZnO particles; both of the approaches were used in the aim to improve optical properties of zinc oxide in comparison with bulk one. The synthesized powders were characterized by X-ray powder diffraction (XRD), Raman spectroscopy, field emission scanning electron microscopy (FESEM), UV-Vis diffuse reflectance spectroscopy (UV-Vis DRS) and photoluminescence (PL). It was found that point defects (oxygen vacancies and zinc interstitials) were created in the crystal structure of zinc oxide. However, PEO has two-fold role, it passivate surface of the ZnO particles, but also introduce oxygen interstitials on the surface. The influence of the point defects on optical properties of ZnO was studied; it was found that oxygen vacancies, zinc interstitials and oxygen interstitials improved percent of thevisible light absorption, also shift band gap energy toward visible range of the spectrum.

U ovom radu opisan je postupak mikrotalasnog procesiranja nanostrukturnog praha ZnO kao i metoda pripreme nano strukturnog kompozita ZnO/PEO (PEO - polietilen oksid). Uloga mikrotalasnog procesiranja, kao brze metode koja u sistem uvodi veliku količinu energije, bila je da modifikuje kristalnu strukturu ZnO dok je uloga PEO bila da dodatno senzitivizuje površinu čestica ZnO, a sve u cilju modifikovanja (poboljšanja) standardnih optičkih osobina cink oksidnog materijala. Sintetisani prahovi su analizirani metodama rendgenske difrakcije (XRD), Ramanove spektroskopije, skanirajuće elektronske mikroskopije (FESEM), UV-Vis difuzione refleksione spektroskopije (UV-Vis DRS) i fotoluminiscencije (FL). Uočeno je da su se u kristalnoj strukturi ZnO formirali tačkasti defekti, tačnije kiseonične vakancije i intersticije cinka, dok je prisustvo PEO sa jedne strane dovelo do pasivizacije površine čestica, dok je sa druge strane došlo do formiranja kiseoničnih intersticija. Ispitan je uticaj tačkastih defekata na optičke karakteristike prahova ZnO; kiseonične vakancije, kao i intersticije cinka i kiseonika utiču kako na procenat apsorpcije vidljive svetlosti (%) tako i na pomeraj energetskog procepa (eV) ka vidljivom delu spektra