Structure, upconversion photoluminescence, and dielectric properties of Ho3+- and Yb3+-codoped tetragonal tungsten bronze Sr4La2Ti4Nb6O30

Ho3+- and Yb3+-codoped Sr4La2Ti4Nb6O30 (Sr4La1.94–xHo0.06YbxTi4Nb6O30, abbreviated as SLTN: Ho-Ybx) ceramics have been synthesized, and their structural, up-conversion (UC) photoluminescence, and dielectric properties have been carefully investigated. Through Rietveld structural refinement, SLTN: Ho-Ybx samples are determined as single tetragonal tungsten bronze (TTB) phase with space group P4/mbm in which larger Sr2+ ions fill the A2-sites, relative smaller La3+, Ho3+, and Yb3+ ions occupy the A1-sites, while Ti4+ and Nb4+ ions fill the B-sites. Under 980 nm near infrared (NIR) excitation, bright UC green emission, relatively weak red and near-infrared (NIR) emissions, originating from 5F4/5S2 → 5I8, 5F5 → 5I8, and 5F4/5S2 → 5I7 transitions of Ho3+ ions, are confirmed for SLTN: Ho-Ybx. Two-photon energy transfer process is proved through pumping laser power dependence of emission intensity measurement. Furthermore, the influence of Ho3+- and Yb3+- ions on the dielectric properties of SLTN: Ho-Ybx is also investigated and the temperature stability of dielectric permittivity is improved.