Multicolor anti-counterfeiting and naked-eye visual temperature sensing based on niobate double perovskites

Ca₂LuNbO₆:Mn⁴⁺/Dy³⁺ (CLNO:Mn/Dy) phosphor was successfully synthesized by high-temperature solid-state reaction, and exhibited a composite luminescent characteristic composed of f-f transition of Dy³⁺ and d-d transition of Mn⁴⁺. The wavelength-dependent multi-color luminescence regulation from yellow to red was achieved by utilizing the different photoexcitation pathways of Mn⁴⁺ and Dy³⁺. By taking advantage of the inherent excellent thermal stability of inorganic oxides and the different temperature-dependent variations in the luminescence intensities of Mn⁴⁺ and Dy³⁺, a wide-temperature-range visual temperature sensing from red to yellow-green light was achieved by the luminescence intensity ratio (LIR)-based optical thermometry. The luminescence mechanism study showed that the luminescence processes of Mn⁴⁺ and Dy³⁺ are independent of each other. The temperature sensing property was attributed to the different thermal quenching behaviors of Dy³⁺ and Mn⁴⁺. The temperature sensing absolute sensitivity (S_a) and relative sensitivity (S_r) of CLNO:0.2 %Mn⁴⁺/2 %Dy³⁺ sample reached 0.023 K^-1 at 493 K and 1.86 % K^-1 at 473 K, respectively. The research result was significant for the development of multi-color luminescent anti-counterfeiting materials and non-contact visual temperature sensing materials.