Study of the Distribution of Radiative Defects and Reabsorption of the UV in ZnO Nanorods-Organic Hybrid White Light Emitting Diodes (LEDs)

Ijaz Hussain,Yousuf Soomro,Omer Nur,Magnus Willander,Nargis Bano,Sajjad Hussain

doi:10.3390/ma4071260

Abstract

In this study, the low temperature aqueous chemical growth (ACG) method was employed to synthesized ZnO nanorods to process-organic hybrid white light emitting diodes (LEDs) on glass substrate. Electroluminescence spectra of the hybrid white LEDs demonstrate the combination of emission bands arising from radiative recombination of the organic and ZnO nanorods (NRs). Depth resolved luminescence was used for probing the nature and spatial distribution of radiative defects, especially to study the re-absorption of ultraviolet (UV) in this hybrid white LEDs structure. At room temperature the cathodoluminescence (CL) spectra intensity of the deep band emission (DBE) is increased with the increase of the electron beam penetration depth due to the increase of defect concentration at the ZnO NRs/Polyfluorene (PFO) interface and probably due to internal absorption of the UV. A strong dependency between the intensity ratio of the UV to the DBE bands and the spatial distribution of the radiative defects in ZnO NRs has been found. The comparison of the CL spectra from the PFO and the ZnO NRs demonstrate that PFO has a very weak violet-blue emission band, which confirms that most of the white emission components originate from the ZnO NRs.

Highlights

Zinc oxide (ZnO) nanostructures possess a promising future owing to the variety of optical and electrical properties which are technologically useful for many nanoscale electronic and photonic devices
The distribution of the radiative defects and reabsorption of the UV are responsible for the wide modification of the luminescence properties of hybrid white light emitting diodes (LEDs) based on ZnO NRs
The room temperature (RT)-EL measurement of the ZnO nanorods-organic hybrid white LEDs was carried out using a photo multiplier detector under dc-bias conditions

Summary

Introduction

Zinc oxide (ZnO) nanostructures possess a promising future owing to the variety of optical and electrical properties which are technologically useful for many nanoscale electronic and photonic devices. For detailed emission information and to explain the origin of the specific emission from specific small area, or even from individual nanostructures, a probe with high spatial and spectral resolutions is preferable In this respect, depth resolved cathodoluminescence (CL) spectroscopy is a powerful technique for probing the nature of defects, both electronically and spatially on the nanoscale [7,9]. The information derived from the depth resolved luminescence provides a tool for the growth and processing the state-of-the-art hybrid white LEDs. The distribution of the radiative defects and reabsorption of the UV are responsible for the wide modification of the luminescence properties of hybrid white LEDs based on ZnO NRs. it is important to obtain a detailed information of the luminescence and verify the origin of specific emissions from ZnO nanorods-organic hybrid white LEDs

Results and Discussion

Experimental Section

Conclusions