Optical and Structural Characteristics of Rare Earth-Doped ZnO Nanocrystals Prepared in Colloidal Solution

Abstract

ZnO nanocrystals doped with Nd, Gd, and Er were synthesized using a soft chemical process in ambient atmosphere. Pseudospherical and hexagonal nanocrystals (NC) of the wurtzite phase with a mean size of (7.4 ± 1.7) nm were obtained. The presence of rare earth (RE) dopants was confirmed by X-ray fluorescence (XRF) spectroscopy. The ZnO nanocrystals exhibited simultaneously narrow excitonic- and broad trap/surface-related photoluminescence (PL), both of which were affected by doping with RE atoms. Doping reduced the total PL intensity, suppressing the excitonic emission by a greater extent than the broad band PL. Also, doping resulted in a blue shift of the trap/surface-related emission, while the energy of the excitonic peak remained unchanged. Resonant Raman spectra additionally confirmed the wurtzite phase of ZnO NCs and revealed a shift of the A1-LO mode towards lower frequency upon doping that could be caused by the mass effect of RE atoms, point defects, and increases in charge carrier concentration. Fitting of the spectra with Voigt profiles showed better results with two surface optical (SO) phonon modes that were previously theoretically predicted for the wurtzite ZnO phase. The influence of RE doping on PL and Raman spectra can be explained by the incorporation of RE ions into the ZnO nanostructures, where the dopants act as non-radiative defects.

ZnO and Ag NP-decorated ZnO nanoflowers: green synthesis using Ganoderma lucidum aqueous extract and characterization

“…35 In the NPs, the LO peak and its overtones usually dominate the Raman spectrum under the resonant excitation with a 325 nm laser source. 4,36,37 The moderate intensity of the LO and 2LO features and their comparable intensity in our non-resonant spectra are fully consistent with the 12–13 nm size of the nanocrystallites obtained from the XRD measurements.…”

“…37,38 The excitonic PL (EPL) is more typical for NPs and polycrystalline lms obtained at higher temperatures, 36,39 while NPs synthesized under mild conditions also showed pronounced EPL in some previous work. 37,40 The spectrum of the as-synthesized ZnO NPs in the present work exhibits distinct bands centered at 460 and 550 nm, and another band is seen as a shoulder at 415 nm (Fig. 4a).…”

“…ZnO NPs synthesized in water or under other mild conditions usually exhibit only a broad-band PL in the visible range, centered around 550 nm, attributed to defects such as oxygen vacancies (primarily on the NP surface). 37,38 The excitonic PL (EPL) is more typical for NPs and polycrystalline lms obtained at higher temperatures, 36,39 while NPs synthesized under mild conditions also showed pronounced EPL in some previous work. 37,40 The spectrum of the as-synthesized ZnO NPs in the present work exhibits distinct bands centered at 460 and 550 nm, and another band is seen as a shoulder at 415 nm (Fig.…”

“…Modifying the NP surface is a well-known approach to both modifying the properties of the NPs and clarifying the nature of some properties, particularly the origin of different PL bands. 40,45,46 Dimethyl sulfoxide (DMSO), for instance, a very useful solvent, miscible with water, oen used in biomedical applications and the synthesis of nanoparticles, [47][48][49] was shown to be an efficient stabilizer of the ZnO colloidal NPs, 37,38 ensuring a very high intensity of both surface-related (DPL) 38,45 Fig. 3 XRD patterns (a) and Raman spectra (b) of ZnO NPs synthesized using G. lucidum extract.…”

“…Raman spectra for sample #1 were measured at different laser powers: 10 4 W cm −2 (curve 1) and 10 5 W cm −2 (curve 2). and excitonic (EPL) 37,40 bands. Therefore, we investigated the inuence of adding DMSO (aer synthesis) on the PL spectrum of the present ZnO NPs.…”