Photoluminescence and structural characteristics of double tungstates A(M1−X PrX)W2O8 (A = Li, Cs, M = Al, Sc, La)

In this article, photoluminescence of Pr3+ ions in the double tungstate A(M1−X PrX)W2O8 (A = Li, Cs, M = Al, Sc, La; 0.0 ≤ X ≤ 0.1) are characterised. By varying ion radius in A and M sites the crystal structure was modified and even in crystals with similar structural characteristics three distinctive types of luminescence are observed. When the substitution ions in both A and M sites are relatively small the host lattice exhibits luminescence dominantly. With the small A site ion (Li+) and the large M site ion (La3+, 1.03 Å) the Pr3+ ion exhibits prominent luminescence. With the very large A site ion (Cs+, 1.67 Å) and relatively small M site ion (Sc3+, 0.75 Å) the Pr3+ exhibits both the 4f2–4f5d excitation and the 3PJ manifold excitations in the absorption spectrum. These excitation levels lead to two strong emissions from the Pr3+. PL characteristics are discussed with respect to crystal structural criteria.