Luminescence enhancement effects of Ca Sr2‒Nb2O7:Er3+,Tm3+ phosphors for temperature sensing and anti-counterfeiting applications

Er3+- and Tm3+-doped CaxSr2‒xNb2O7 (CxS2‒xN, x = 0.6, 0.8, 1.0, 1.2, 1.4) phosphors with layered perovskite structure were designed. These phosphors exhibit a dominant emission peak at 549 nm under 980 nm laser excitation, attributed to the 4S3/2→4I15/2 transition. By increasing the content of Ca2+, the crystal field regulation of rare earth ions is realized and the luminescence enhancement is induced, which is manifested by the increase of 2H11/2,4S3/2→4I15/2 emission. Furthermore, the temperature sensing sensitivities of C0.6S1.4N:Er,Tm and C0.6S1.4N:Er,Tm based on non-thermally coupled energy levels were studied. Finally, an anti-counterfeiting imprint was prepared using phosphors, which have high brightness and excellent photothermal stability. This work not only confirms that closer ionic radii substitution enables to increase the electronic density of states, improve the crystal field symmetry and enhance the luminescence, but also provides a promising phosphor system for temperature sensing and anti-counterfeiting applications, opening up new prospects in the optimization of the optical properties of phosphors.