Size control and luminescence properties of Eu~(2+):LiCaAlF_6 particles prepared by femtosecond pulsed laser ablation

摘要

We have fabricated Eu~(2+):LiCaAlF_6 (Eu:LiCAF) nanoparticles via a dry pulsed laser ablation process using femtosecond laser pulses. The particle size was controlled by adjusting the laser fluence. The crystallographic orientation and chemical composition were preserved in all particles. The typical luminescence peak of Eu:LiCAF crystals at approximately 370 nm was observed in both the PL and X-ray induced luminescence (XL) spectra. The temporal PL profiles of all deposited particles exhibited fast-decay components in addition to the slow-decay components observed in the profile of the bulk crystal. Smaller particles had shorter decay times than larger particles. The fast-decay component of particles with a mean diameter of less than 0.36 μm (∼40 ns) was at least one order of magnitude shorter than the decay time of the bulk crystal (∼1700 ns). Even in the temporal XL profile, all deposited particles showed shorter decay times than the bulk decay time. We attribute these fast-decay components to defects on the particle surface. To confirm the defect level, we investigated the thermally stimulated luminescence of the deposited particles. In addition to an emission peak at approximately 540 K, which was also observed in the spectrum of the bulk crystal, an emission peak corresponding to surface defects at approximately 700 K was observed in the spectrum of the particles.