Improvement of Quantum Efficiency of the Nanosized Phosphors Using a Flux

Abstract

Micron-sized phosphors have been widely researched for a near UV-LED by the mean of the convenient solid-state method. The phosphors with micron-sized tend to show good quantum efficiency oriented from their large crystallite size, but present high light-scattering and decrease packing density on the LED device, causing low resolution. Therefore, integration of the phosphors for a near-UV LED package has particles size requirements in order to overcome the issue from bulk size phosphors. The scatter effect in visible and UV radiation region will be negligible when the radii of phosphors particles are less than ~400 nm. However, phosphors with nano-size particles have poor quantum efficiency comparing to phosphors with micron sized particles. In this work, flux effect on quantum efficiency is studied in nano-sized phosphors. Blue colored CaMgSi2O6:Eu2+ phosphors were synthesized by a co-precipitation method and NH4F, NH4Cl, or H3BO3 was added as a flux. Flux is typically used in the solid-state reaction to help diffusion of atoms in the bulk materials, not nano-sized materials. The crystallite size is increased from ~20 nm to ~40 nm, but particles size is unchanged (~ 50 nm) with the addition of a flux in the materials, confirmed by X-ray diffraction, Dynamic Light Scattering analysis, and Scanning Electron Microscopy. The emission wavelength of CaMgSi2O6:Eu2+ is 458 nm under 350 nm as an excitation wavelength. The intensity of emission wavelength is about twice increased when 5wt% NH4F is added as a flux in the phosphors materials comparing to the phosphors without a flux, indicating the improvement of quantum efficiency. This study shows the potential of flux that could improve quantum efficiency in the nano-sized phosphors. This work is supported by the National Science Foundation, Ceramics Program Grant (DMR-1411192).