Effects of Er3+ concentration on down-/up-conversion luminescence and temperature sensing properties in NaGdTiO4: Er3+/Yb3+ phosphors

Usually, Er3+ doping concentration effect on the temperature sensing properties of Er3+ containing materials is ignored. In this work, we demonstrated the influence of Er3+ concentration and excitation path on the spectral and temperature sensing properties in Er3+, Yb3+ co-doped NaGdTiO4 system. The NaGdTiO4: Er3+/Yb3+ phosphors were prepared by a high temperature solid state reaction method. Different spectral patterns for down- and up-conversion processes were observed and ascribed to the different excitation and population routes. The concentration quenching behaviors for down- and up-conversion processes were explained via cross relaxations between Er3+ ions. Most importantly, the Er3+ concentration dependent optical temperature sensing performance was observed and experimentally explained as a fact that the optical transition rate of Er3+ in different samples was changed with various Er3+ doping concentration.