On-off blinking and multiple bright states of single europium ions in Eu3+: Y2O3 nanocrystals

We show that continuously illuminated single europium ions incorporated in yttrium oxide (Eu3+:Y2O3) nanocrystals (5-15 nm diameter) undergo on-off bl inking on a variable time scale ranging from hundreds of milliseconds to se veral seconds. We observe both a pump-intensity dependent "duty factor" (on -time as a percentage of total measurement time), and quantum jumps between at least three well-defined luminescence intensity levels (bright states) from individual nanoparticles. Interesting switching or oscillation between different bright levels was also observed with a modulation rate that is d ependent on pump-laser intensity. These features of single-ion luminescence are not observed for larger particles with multiple chromophores. We propo se that these effects derive from pump laser-induced fluctuations between d ifferent quasi-stable Eu3+ symmetry sites that effectively modulate the ele ctric dipole transition moment.