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

Photoluminescence (PL) and cathodoluminescence (CL) properties of Ln(3+) (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:Ln(3+)/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:Ln(3+)/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.