We demonstrated that visible surface plasmon polaritons (SPPs) were excited at the metallized interface of indium-tin-oxide (ITO)-coated iron doped Y-cut and Z-cut lithium niobate (Fe  :  LiNbO₃, Fe:LN) slabs, where large angle scattering and light tracks were observed on the surface. After introducing active erbium element, it was found that SPPs’ excitation could greatly affect upconversion emission (UCE) in Er,Fe:LN crystal samples. This surface effect was more attractive when increasing the surface-to-volume ratio with powdered form. In the ITO-coated Er,Fe:LN specimen, dynamic variations of huge UCE dropping-down and gradual rising were observed, which is a result of energy loss via coupling to SPPs. Our work supports an opportunity in designing plasmonic nanometric light sources, leading paths toward implementing spasers apart from lossy metals in photonic waveguides.