Structure, morphology and optical characterization of Dy3+-doped BaYF5 nanocrystals for warm white light emitting devices

The barium yttrium fluoride BaYF5 nanocrystalline powders doped with different concentrations of Dy3+ ions have been synthesized via a hydrothermal method and studied their structural, morphological, thermal, vibrational, and optical properties. These nanopowders have been crystallized in a single phase of the tetragonal structure with the average size of around 30 nm having spherical shape in morphology. Upon excitations at 350 and 387 nm, Dy3+ -doped BaYF5 nanocrystals exhibit strong blue and yellow emissions ascribed to the 4F9/2 → 6H15/2 and 4F9/2 → 6H13/2 transitions, respectively. Decay curves of the 4F9/2 level of Dy3+ ion in BaYF5 nanocrystals exhibit non-exponential nature due to the dipole-dipole interaction between Dy3+ ions, confirmed by Inokuti-Hirayama model. The quantum yield for these nanocrystals have been found to be increased from 4.64% to 11.61% as the concentration of Dy3+ ions increases from 1.0 mol% to 2.0 mol% and then decreased to 10.68% as the dopant concentration increased to 5.0 mol%. Moreover, color coordinates and correlated color temperatures have been evaluated as a function of concentration and excitation wavelength and found to be in the warm white light region for all Dy3+ concentrations.