Multicolor luminescence and energy transfer of KSrGd(PO4)2:Ln3+ (Ln = Ce, Sm, Eu, Tb, Dy, Dy/Eu, Yb/Ho, Yb/Er, Yb/Tm) phosphors for WLED and multiple anti-counterfeiting

KSrGd(PO 4 ) 2 :Ln 3+ (Ln = Ce, Sm, Eu, Tb, Dy, Dy/Eu, Yb/Ho, Yb/Er, Yb/Tm) phosphors were synthesized by high temperature solid state method. Doping the KSrGd(PO 4 ) 2 matrix with 5%Dy 3+ ions resulted in white light emission under 345 nm excitation. The calculated color temperature (CCT) of this white light is 5523 K, indicating as positive white light. It was found that the luminous intensity of the obtained KSrGd(PO 4 ) 2 :5%Dy 3+ at 200 °C was 76.80 % of that at room temperature, showing good thermal stability as well as possibility of application in white LED. Under the excitation at 392 nm, the fluorescence quantum yield of KSrGd(PO 4 ) 2 :10%Eu 3+ is 79.92 %. Energy transfer between Dy 3+ and Eu 3+ is observed in KSrGd(PO 4 ) 2 :Dy 3+ /Eu 3+ samples, with identified mechanism as the quadrupole-quadrupole interaction. Tunable luminescence ranging from white to yellow then to orange-red is achieved by adjusting the doping concentration of Eu 3+ in KSrGd(PO 4 ) 2 :5%Dy 3+ , x%Eu 3+ . Under the excitation of 980 nm near-infrared light, the prepared KSrGd(PO 4 ) 2 :Yb 3+ /Ho 3+ , KSrGd(PO 4 ) 2 :Yb 3+ /Er 3+ and KSrGd(PO 4 ) 2 :Yb 3+ /Tm 3+ samples showed up-conversion emissions of red, yellow and blue, respectively, with two-photon processes. In KSrGd(PO 4 ) 2 matrix, multi-color and multi-security marks were successfully prepared by utilizing up/down conversion luminescence characteristics, which obtained good anti-counterfeiting effect and improved anti-counterfeiting security. Therefore, the obtained KSrGd(PO 4 ) 2 : Ln 3+ phosphors exhibit promising application prospects in the fields of WLED and multiple anti-counterfeiting.