Dependence of photoluminescent properties of cubic Y_2O_3:Tb~(3+) nanocrystals on particle size and temperature

摘要

Temperature-dependent spectral properties in the cubic Y_2O_3:Tb~(3+) 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 ~5D_4-~7F_J (J = 1-6) transitions of Tb~(3+) ions and a broad band originated from oxygen defects were observed. As a function of temperature, two intensity maximums of the ~5D_4-Σ~7F_J 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 Tb~(3+) centers, the internal and the surface. The emission for the surface Eu~(3+) centers has higher quenching temperature in contrast to that for the internal centers.