Improved Response of Upconversion Luminescence Color to Pump Power through the Coupling of Er³⁺ and Tm³⁺

Upconversion materials activated with Er³⁺ have been demonstrated to be potential candidates for multi-color displays, dynamic fluorescence anti-counterfeiting, and so forth. However, due to the similar upconversion pathways for green and red emissions, it remains a challenge to realize highly sensitive multi-color upconversion luminescence by adjusting the laser power. Here, based on Er₂Mo₄O₁₅ without concentration quenching of luminescence, we demonstrated that the incorporation of heterogeneous Tm³⁺ impurities could significantly improve the response of luminescence color to laser power. Through solving a set of rate equations, it was clarified that the power-dependent depletion of the ⁴I_11/2 level was responsible for the modulation of luminescence color. Also, it was proved that the enhancement of luminescence was in relation to the blocked energy migration and enhanced radiative transition probability. Our work provides an effective approach to improve the power response of luminescence colors based on the photon upconversion of Er³⁺.