Eu3+ doped KYF4 nanocrystals: synthesis, electronic structure, and optical properties

Monodisperse cubic-phase KYF(4) : Eu(3+) nanocrystals (NCs) were synthesized via a modified thermal decomposition method. The optical properties of Eu(3+) in KYF(4) NCs including multiple luminescence centers, site symmetry, luminescence dynamics, as well as crystal-field levels of Eu(3+) were investigated in detail based on high-resolution photoluminescence (PL) spectroscopy at low temperature (10 K). Different from Eu(3+) in bulk counterparts, multiple sites of Eu(3+) in KYF(4) NCs were revealed by using the luminescence of Eu(3+) as a sensitive structural probe. The highest site symmetry of Eu(3+) at new near-surface site was deduced to be distorted from O(h) to D(2) (or C(2v)). Due to a small filling factor (0.45) of NCs, the PL lifetime of (5)D(0) of Eu(3+) in KYF(4) NCs was much longer than that in bulk counterparts, which was found to be significantly affected by the surrounding medium around the NCs.