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

T. Wei,C.P. Li,Q.J. Zhou,Z.P. Li,P. Li,J. Wu,X.F. Yang

Ho 3+ - and Yb 3+ -codoped Sr 4 La 2 Ti 4 Nb 6 O 30 (Sr 4 La 1.94– x Ho 0.06 Yb x Ti 4 Nb 6 O 30 , abbreviated as SLTN: Ho-Yb x ) ceramics have been synthesized, and their structural, up-conversion (UC) photoluminescence, and dielectric properties have been carefully investigated. Through Rietveld structural refinement, SLTN: Ho-Yb x samples are determined as single tetragonal tungsten bronze (TTB) phase with space group P 4 /mbm in which larger Sr 2+ ions fill the A 2 -sites, relative smaller La 3+ , Ho 3+ , and Yb 3+ ions occupy the A 1 -sites, while Ti 4+ and Nb 4+ 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 5 F 4 / 5 S 2   →   5 I 8 , 5 F 5   →   5 I 8 , and 5 F 4 / 5 S 2   →   5 I 7 transitions of Ho 3+ ions, are confirmed for SLTN: Ho-Yb x . Two-photon energy transfer process is proved through pumping laser power dependence of emission intensity measurement. Furthermore, the influence of Ho 3+ - and Yb 3+ - ions on the dielectric properties of SLTN: Ho-Yb x is also investigated and the temperature stability of dielectric permittivity is improved.