Photoluminescence enhancement of PEG-modified YAG:Ce³⁺ nanocrystal phosphor prepared by glycothermal method

Y₃A1 ₅O₁₂:Ce₃₊ (YAG:Ce3+) nanocrystals were synthesized in 1,4-butylene glycol (BG) with and without poly(ethylene glycol) (PEG) by the glycothermal method. The internal quantum efficiency of the photoluminescence (PL) corresponding to the 5d →4f transition of Ce³⁺in the YAG:Ce³⁺nanocrystal increased from 21.3 to 37.9% by addition of PEG, while no appreciable change in the primary particle size, the crystallite size, and the lattice distortion was recognized by transmission electron microscopy and X-ray diffractometry. The thermogravimetry-differential thermal analysis, Fourier transform infrared absorption spectroscopy and ¹H → ¹³C cross-polarization magic angle spinning nuclear magnetic resonance (CP-MAS NMR) confirmed the preferential coordination of PEG to the YAG:Ce³⁺ nanocrystal. ²⁷ A1 single-pulse excitation MAS NMR reveals that the ratio of the 4-fold coordination site to the 6-fold coordination site increased from 0.53 to 0.72 by addition of PEG. We conclude that the surface modification of the YAG:Ce³⁺ nanocrystal by PEG induces the surface passivation, the prevention of the oxidation of Ce³⁺ to Ce⁴⁺, the promotion of the incorporation of Ce³⁺ into YAG and the local structural rearrangement, resulting in the PL enhancement.