Composition and excitation wavelength dependent photoluminescence color tuning in nanocomposite of PMMA and ZnO nanorods for PLED

Abstract

Semiconducting nanocomposites of PMMA and ZnO are obtained by bulk polymerization of MMA in presence of hydrothermally synthesized ZnO nanorods. Three different phenomena i.e. FRET from PMMA to ZnO, red edge effect in PMMA, self-absorption in ZnO are found to be mainly responsible for the tunable luminescence in PMMA-ZnO nanocomposite. At excitation wavelength 285 nm, due to significant overlap between emission spectrum of PMMA and absorption spectrum of ZnO, FRET occurs from PMMA to ZnO and enhanced blue emission from the composite is obtained. Due to self-absorption in ZnO, the emission shows red shift up to few nanometers with increase in ZnO content. Again the energy transfer efficiency decreases with increase in ZnO content in the composite due to which emission intensity also decreases. Due to red edge effect the emission from PMMA shifts towards higher wavelength with the red shift of excitation wavelength. This causes no spectral overlap between PMMA and ZnO and no significant FRET occurs at excitation wavelength 377 nm. Here the emission from both PMMA and ZnO is observed and with increment of ZnO content the emission from ZnO becomes dominant. Thus with proper tuning of ZnO content in the composite, the emission from the composites excellently changes from deep blue to white upon illumination with photon of wavelength 377 nm. To get an insight of the applicability of the composites for polymer light emitting diode (PLED), electroluminescent property of the composites is investigated with the help of a mathematical model. From the calculated results, the external quantum efficiency (ηext) using the nanocomposite with 5 wt% of ZnO as emissive layer which emits light of wavelength 440 nm, is found to be the highest i.e. 5% at a turn-on voltage of 2.6 V. The other composites also show quite good ηext and hence become promising candidates for application in blue as well white light emitting PLED.