Concentration effect on up-conversion luminescence and excitation path-dependent luminescence temperature quenching...

Usually, the luminescence intensity and mechanism of rare-earth ions doped materials are dependent on both doping concentration and sample temperature. In this study, we attempt to explore the concentration effect on up-conversion (UC) luminescence and the dependence of luminescence temperature quenching on excitation wavelength in YNbO₄: Ho³⁺/Yb³⁺ phosphors. The YNbO₄: Ho³⁺/Yb³⁺ phosphors with various Ho³⁺ and Yb³⁺ concentrations were synthesized via a high-temperature solid-state reaction technique. Intense green UC emission peaked at 543 nm was observed, accompanying with weak red and near infrared (NIR) UC emissions centered at 659 and 745 nm. Based on the laser working current dependence of UC luminescence, two-photon processes were responsible for both the green and the red UC emissions under 980 nm excitation, which have no apparent dependence on both Ho³⁺ and Yb³⁺ concentrations. According to the Arrhenius model, crossover process was responsible for the temperature-dependent down-conversion (DC) luminescence quenching of Ho³⁺ under 452 nm excitation. However, the temperature quenching processes of the green and the red UC luminescence cannot be well explained by Arrhenius model. It was found that the UC luminescence intensity decayed with increasing sample temperature, which was caused by both the crossover and temperature-dependent energy transfer processes.