X-ray Excited Optical Luminescence Studies of ZnO and Eu-Doped ZnO Nanostructures

Abstract

Pure (ZnO) and Eu-doped ZnO (Eu:ZnO) nanostructures have been grown in different morphologies by thermal evaporation. The growth of the structures depends on the temperature and concentration gradient during material deposition as well as on the doping species. X-ray excited optical luminescence (XEOL) from nanostructured ZnO and Eu:ZnO shows a correlation of optical properties with morphology on a nanoscale. In particular, the relative intensity of band gap and defect emission (green light) changes drastically in Eu:ZnO and ZnO nanostructures with different morphology. In this Article, we present experimental results from Eu:ZnO and ZnO nanostructures, using synchrotron radiation-based XEOL, time-gated XEOL, and element specific XANES with partial and total photoluminescence yield (PLY). Our results suggest that the rare earth dopant most likely affects the energy transfer and structural changes by nucleation, rather than direct radiative decay from Eu sites.

Obtaining strong ferromagnetism in diluted Gd-doped ZnO thin films through controlled Gd-defect complexes

“…22 The peaks are pronounced in GdZnO films due to strong O 2p state hybridization with the Gd 4f and Zn 3d states. 23 The intensity of these peaks increases with Gd concentration, confirming that they arise from hybridization and are associated with a decrease in the occupation of O 2p states. This is related to the higher electronegativity of Gd relative to Zn.…”

The Origin and Dynamics of Soft X‐Ray‐Excited Optical Luminescence of ZnO

“…The nanoneedles form in a warmer region while the microcrystallites form in a colder one. [29,32] The nanosample has an average tapering radius of tens to several nm and a base of larger nanocrystallites of 0.1-1 mm, which aggregate in clusters of 5-10 mm. The microsample has a characteristic size in the 1-10 mm range (Figure 1).…”

“…[29,32] Two different ZnO morphologies were selected for this study (Figure 1), namely nanoneedles and microcrystallites, henceforth denoted nanosample and microsample respectively. Indeed, through a careful control of synthesis parameters, oxide structures in a steadily changing morphology are grown due to a substrate temperature gradient (see the Experimental Section).…”

“…Herein we show that tunable soft X-rays and nanosized ZnO structures make it easier to investigate the effects of site specificity of XEOL in a greater detail. [32] Soft X-rays have a rather shorter penetration depth, for example,~200 nm at the O K edge (~540 eV) and the Zn L 3,2 edge (~1130 eV) for ZnO. [33] According to the universal curve for electron escape depth, [34] the emitted Auger electrons (~500-1000 eV kinetic energy) have an attenuation length (mean free path) of 5-10 nm in the solid.…”

XANES and photoluminescence studies of crystalline GeO2(Tb) nanowires

“…GeO 2 (Tb) NWs on a SiO 2 (silica) substrate were prepared by vapor deposition in a horizontal tube furnace as described previously [9][10][11]. Ge powder (99.9%, Alfa Aesar) was used as source compounds for GeO 2 .…”