Facile solvothermal synthesis of high refractive index ZrO2 spheres: estimation of the enhanced light extraction efficiency

Abstract

Sub-micron sized ZrO₂ spheres were synthesized by a facile solvothermal reaction method. The influence of Zr(OPr)₄ concentration on the size and size distribution of ZrO₂ spheres were examined by taking the scanning electron microscope and transmission electron microscope images. When the concentration of Zr(OPr)₄ was increased from 0.031 to 0.045 mol, the average size of the spheres also increased from 305 to 920 nm. The diffused reflectance spectra of the calcined ZrO₂ spheres exhibited the higher reflectivity than that of as-prepared ZrO₂ spheres. As compared to the bare LEDs, light extraction efficiency was improved to 23% when the ZrO₂ spheres were coated on the ITO surface, however, 70.12% was improved when the ZrO₂ spheres were coated on the GaN surface due to the spherical morphology induced photon escape cone enhancement.