Optical thermometry using Stark sublevels in charge compensated transition metal molybdate upconverting phosphors

A series of anorthic phased Er3+/Yb3+/Li+/K+: ZnMoO4 phosphors have been synthesized by solid state reaction method. Under 980 nm excitation, Er3+-Yb3+ codoped phosphors exhibit intense green emission at similar to 531 nm/similar to 553 nm corresponding to the H-2(11/2)/S-4(3/2) -> I-4(15/2) and weak blue and red emissions at similar to 408 nm, similar to 474 nm and similar to 656 nm corresponding to the( 2)H(9/2) -> I-4(15/2), F-4(7/2) -> I-4(15/2) and F-4(9/2) -> I-4(15/2) transitions, respectively. The multipolar interaction is found responsible for the concentration quenching. Furthermore, with incorporating the charge compensating agents Li+/K+ the UC emission intensity as well as temperature sensing performance have been perceptibly improved compared to the Er3+-Yb3+ phosphors. The fluorescence intensity ratio (FIR) technique have been performed to the thermally coupled (H-2(11/2), S-4(3/2)) levels and Stark sublevels (H-2(11/2), S-4(3/2(I)) & H-2(11/2), S-4(3/2(II))) to confirm the temperature sensing ability of the phosphors. The maximum sensitivity corresponding to the H-2(11/2), S-4(3/2(I)) -> I-4(15/2) & H-2(11/2), S-4(3/2(II)) -> I-4(15/2) transitions from the Stark sublevels have been observed.