Upconversion luminescence through dynamically regulating the depletion of Ho3+: 5I6 level for speed sensing

Abstract

In this work, a strategy for dynamically adjusting the upconversion luminescence (UCL) color of NaGdF4:Yb3+/Ho3+/Ce3+/Sc3+ is reported based on a phosphor wheel. It has been demonstrated that the rotation-dependent UCL mainly originated from the regulation of depletion mode for the Ho3+: 5I6 level. Due to the dominant linear decay, a high-pure red UCL is observed under the steady-state excitation. However, as the proportion of the steady-state excitation decreases, the green–red emission intensity ratio gradually increases, followed by the color conversion from red to green. An approximate physical model is proposed to understand the dependence of IG/IR on rotation speed. We not only report a UCL material that shows potential application in velocity sensing but also provide new insights into wheel-based dynamic UCL regulation.