Photoluminescence and structural characteristics of double tungstates A(M_(1-x)Pr_x)W_2O_8 (A = Li, Cs, M = Al, Sc, La)

摘要

In this article, photoluminescence of Pr~(3+) ions in the double tungstate A(M_(1-X)Pr_X)W_2O_8 (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 (La~(3+), 1.03 A) the Pr~(3+) ion exhibits prominent luminescence. With the very large A site ion (Cs~+, 1.67 A) and relatively small M site ion (Sc~(3+), 0.75 A) the Pr~(3+) exhibits both the 4f~2-4f5d excitation and the ~3Py manifold excitations in the absorption spectrum. These excitation levels lead to two strong emissions from the Pr~(3+). PL characteristics are discussed with respect to crystal structural criteria.