Enhancing luminescence, tuning emission colors, and improving temperature sensitivity in NaGd(MoO₄)₂ multilayer thin films

A thin film with a sandwich structure of NaGd(MoO₄)₂: Yb³⁺@Yb³⁺/Ho³⁺@Yb³⁺ was successfully prepared using the spin-coating method. A comparative analysis of this sandwich-structured film with other films having the same doping composition and spin coating times showed that the emission intensity of the former was enhanced. We attribute the luminescence enhancement of the sandwich-structured film to the presence of Yb³⁺ ions in both the top and bottom layers. This overcomes the concentration quenching effect imposed by the Yb³⁺/Ho³⁺ system's concentration limit. Moreover, the warm white light emission of the NaGd(MoO₄)₂:Yb³⁺@Yb³⁺/Tm³⁺@Yb³⁺/Ho³⁺@Yb³⁺ film was successfully achieved by introducing Yb³⁺/Tm³⁺ layers, and tuning from blue to white to yellow was realized by adjusting the number of spin coatings and the proportion of Yb³⁺/Tm³⁺ and Yb³⁺/Ho³⁺ layers. Finally, we found that sandwich-structured films have better temperature sensitivity compared to powder materials and other structured films. These results indicate that rare-earth doped NaGd(MoO₄)₂ thin films have great potential in the fields of luminescence, color display, and temperature sensing. The adjustment of luminescence color can be achieved by manipulating the micro/nano film structure, and the spin-coating process can effectively improve the temperature sensing characteristics.