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

Monodisperse cubic-phase KYF4 : Eu3+ nanocrystals (NCs) were synthesized via a modified thermal decomposition method. The optical properties of Eu3+ in KYF4 NCs including multiple luminescence centers, site symmetry, luminescence dynamics, as well as crystal-field levels of Eu3+ were investigated in detail based on high-resolution photoluminescence (PL) spectroscopy at low temperature (10 K). Different from Eu3+ in bulk counterparts, multiple sites of Eu3+ in KYF4 NCs were revealed by using the luminescence of Eu3+ as a sensitive structural probe. The highest site symmetry of Eu3+ 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 D-5(0) of Eu3+ in KYF4 NCs was much longer than that in bulk counterparts, which was found to be significantly affected by the surrounding medium around the NCs.