Multi-channel lifetime thermometry and security films based on Ln (Ln = Sm3+, Tb3+, and Sm3+/Tb3+) doped NaKLaNbO5 phosphors

In this report, we synthesized a series of Sm3+ and Tb3+ single-/co-doped NaKLaNbO5 phosphors using a solidstate reaction technique and studied their crystal structures, elemental compositions, morphologies, and photoluminescence properties (e.g., excitation/emission spectra, concentration-quenching mechanisms, thermal stabilities, chromaticity coordinates, and luminescence dynamics). The optimal doping concentrations of the NaKLaNbO5:Sm3+ and NaKLaNbO5:Tb3+ phosphors were determined to be 0.05 and 0.3 mol, respectively. Additionally, the concentration quenching mechanisms of both the NaKLaNbO5:Sm3+ and NaKLaNbO5:Tb3+ phosphors were verified as electric dipole-dipole interactions. Subsequently, a typical NaKLaNbO5:0.05Sm3+/ 0.3Tb3+ phosphor was prepared and used for multi-channel luminescence lifetime thermometry based on different excitation wavelengths and luminescence centers. Notably, the relative sensitivity values of the NaKLaNbO5:0.05Sm3+/0.3Tb3+ phosphor were calculated to be 0.106 % K-1@463 K (lambda ex = 250 nm, lambda em = 550 nm), 0.074 % K-1@463 K (lambda ex = 250 nm, lambda em = 665 nm), 0.072 % K-1@463 K (lambda ex = 284 nm, lambda em = 550 nm), and 0.091 % K-1@303 K (lambda ex = 284 nm, lambda em = 665 nm), respectively, suggesting that the excitation wavelength and luminescence center affect lifetime sensitivity. Furthermore, the NaKLaNbO5:0.3Tb3+ powder-based films were tested for security applications.