Engineering the Lattice Site Occupancy of Apatite-Structure Phosphors for Effective Broad-Band Emission through...

A series of britholite compounds were synthesized by simultaneous introduction of trivalent La³⁺ and Si⁴⁺ ions into an apatite structure. The variations in the average structure, electronic band structure, and microstructural properties resulting from the introduction of cation pairs were analyzed as a function of their concentration. The effects of the structural variance and microstructural properties on the broad-band-emitting activator ions were studied by introducing Eu²⁺ ions as activators. For the resulting compound, which had dual emission bands in the blue and yellow regions of the spectrum, the emission peak position and strength were dependent upon the concentration of La³⁺-Si⁴⁺ pairs. By engineering the relative sizes of the two possible activator sites in the structure, 4f and 6h, through the introduction of a combination of trivalent La³⁺ and a polyanion, the preferential site occupancy of the activator ions was favorably altered. Additionally, the activator ions responsible for the lower-Stokes-shifted blue component of the emission functioned as a sensitizer of the larger-Stokes-shifted yellow-emitting activators, and predominantly yellow-emitting phosphors were achieved. The feasibility of developing a white light-emitting solid-state device using the developed phosphor was also demonstrated.