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 (image) 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.