Concentration Dependent Fluorescence Lifetime in Nanocrystalline Y₂O₃:Eu Phosphors

Nanocrystalline (Y1-xEux)2O3 powder was synthesized via a chemical vapour reaction. Xray diffraction revealed the structure of cubic yttria with crystallite sizes of about 5 nm. The Eudopand concentrations x for the samples in the range from 0.003 up to 0.165 were determined by EDX-spectra. The luminescence of the nanopowders was investigated by continuous and timeresolved UV-fluorescence spectroscopy and compared to a microcrystalline Y2O3:Eu phosphor as a reference. The emission spectra show an increasing intensity for higher doping concentrations. However, compared to the microcrystalline material the yield was significantly lower. The lifetime of the 5D0 – 7FJ transition in the nanocrystalline Y2O3:Eu was found to be significantly longer than for the microcrystalline reference sample. For increasing Eu-content the lifetime in the nanocrystalline samples decreased continuously from 3.71 ms to a value of 1.20 ms for the highest doping concentration. The concentration dependent lifetime behaviour was interpreted by energy transfer between Eu ions and from Eu ions to impurities as a competing process to the radiative 5D0 – 7F2 transition.