(K1.5Eu0.5)Ta₃O₁₀: A Far-Red Luminescent Nanosheet Phosphor with the Double Perovskite Structure

Eu 3+ -activated double perovskite-type nanosheet phosphor (K 1.5 Eu 0.5 )Ta 3 O 10 has been prepared by the soft chemical exfoliation reaction of K(K 1.5 Eu 0.5 )Ta 3 O 10 bulk precursor. The lateral size of the nanosheet product ranges from 0.1 to a few micrometers, and the thickness is uniformly 2.4(2) nm. The lattice parameter along the sheet direction obtained by the in-plane X-ray diffraction is 0.3933(3) nm, corresponding to the typical O−Ta−O distances. The photoluminescence emission can be obtained either by host or by direct photoactivator excitation, but the host excitation yields much higher emission intensity than does the direct photoactivator excitation. The emission spectra show relatively sharp peaks from the 5 D 0 → 7 F J manifold transitions of Eu 3+ . The highest emission intensity is observed around 704 nm (far-red) from the 5 D 0 → 7 F 4 transition of Eu 3+ .