Dependence of photoluminescent properties of cubic Y2O3:Tb3+ nanocrystals on particle size and temperature

Temperature-dependent spectral properties in the cubic Y2O3:Tb3+ nanocrystals (NCs, 10-70 nm) under 488 nm excitation were studied and compared to that in the bulk. In NCs, emission lines assigned to the 5D4-7FJ (J=1-6) transitions of Tb3+ ions and a broad band originated from oxygen defects were observed. As a function of temperature, two intensity maximums of the 5D4-Σ7FJ transitions appeared in the NCs, at ∼250 and ∼500 K, while in the bulk only one maximum appeared at ∼250 K. The relative intensity of the maximum at ∼500 K to that at ∼250 K increased with decreasing particle size. The intensity maximum of the band emissions that came from the oxygen defects appeared in the range of 500-600 K. The appearance of intensity maximum as a function of temperature was attributed to the rivalry between thermal quenching process and phonon-assisted excitation. The appearance of two maxima in the NCs was attributed to the luminescence contributed by different Tb3+ centers, the internal and the surface. The emission for the surface Eu3+ centers has higher quenching temperature in contrast to that for the internal centers.