Designing multi-mode optical thermometers via the thermochromic LaNbO4:Bi3+/Ln3+ (Ln = Eu, Tb, Dy, Sm) phosphors

LaNbO4:1.0%Bi3+/x%Ln3+ (Ln = Eu, Tb, Dy, Sm) phosphors, which can emit both emissions of Bi3+ and Ln3+ ions, were prepared by a solid-state reaction technology. At 306 nm excitation, the prepared phosphors present multi-color emissions due to the energy transfer from Bi3+ to Ln3+ ions. Taking advantage of the various thermal quenching properties between Bi3+ and Ln3+ ions, the optical thermometric characteristics of the resultant compounds were evaluated. The maximum Sa values of the prepared phosphors with the dopants of Bi3+/Eu3+, Bi3+/Tb3+, Bi3+/Dy3+ and Bi3+/Sm3+ are 0.044 K−1, 0.041 K−1, 0.008 K−1 and 0.031 K−1, respectively, while their maximum Sr values are 1.89% K−1, 2.36% K−1, 1.26% K−1 and 1.36% K−1, respectively. Moreover, based on the thermochromic behaviors of the studied samples, their temperature sensing abilities are also explored. Furthermore, through monitoring the temperature-dependent decay time of Bi3+ ions, the maximum relative temperature sensitivity values of the designed phosphors with the dopants of Bi3+/Eu3+, Bi3+/Tb3+, Bi3+/Dy3+ and Bi3+/Sm3+ are 0.10%, 0.032%, 0.037% and 0.145% K−1, respectively. Additionally, the thermometric properties of the compounds can be facilely manipulated by adopting diverse sensing technology. These results indicate that LaNbO4:1.0%Bi3+/x%Ln3+ (Ln = Eu, Tb, Dy, Sm) phosphors are promising multi-mode optical thermometers.