Tunable luminescence and energy transfer properties in KCaGd(PO4)2:Ln3+/Mn2+ (Ln = Tb, Dy, Eu, Tm; Ce, Tb/Dy) phosphors with high quantum efficiencies

Abstract

Photoluminescence (PL) and cathodoluminescence (CL) properties of Ln³⁺ (Ln = Tb, Dy, Eu, Tm, Ce) and Mn²⁺-activated KCaGd(PO₄)₂ (KCG) phosphors were investigated. Under UV excitation, KCG:Tb³⁺, KCG:Dy³⁺, KCG:Eu³⁺, KCG:Tm³⁺, and KCG:Mn²⁺ samples exhibit the characteristic emission of the activators, respectively. By altering doping activators and adjusting their relative doping concentrations in the KCG host, we obtained white emission in KCG:Tm³⁺, Tb³⁺, Eu³⁺, KCG:Tb³⁺, Mn²⁺, Eu³⁺, KCG:Tb³⁺, Eu³⁺, and KCG:Dy³⁺, Eu³⁺ samples under the excitation of 275 or 356 nm UV. Besides, there exist three energy transfer pairs in the KCG host, i.e., Ce³⁺ → Tb³⁺, Ce³⁺ → Dy³⁺, and Ce³⁺ → Mn²⁺. Upon excitation at 280 nm, the absolute quantum yield of the optimized KCG:Ce³⁺, Tb³⁺ is 90.6%. Under the low-voltage electron beam excitation, the CL properties of KCG:Ln³⁺/Mn²⁺ phosphors have been investigated in detail, and a variety of colors can be obtained in these samples. All of the results of this study reveal that the as-prepared KCG:Ln³⁺/Mn²⁺ phosphors have good luminescent intensity under UV and the low-voltage electron beam excitation, especially KCG:Ce³⁺, Tb³⁺ samples, making these materials have potential applications in white-light LEDs and field emission display devices.