Plasmon-enhanced UV and blue upconverted emissions of Tm³⁺-doped 12CaO·7Al₂O₃ nanocrystals by attaching Ag nanoparticles

Tm³⁺-doped 12CaO·7Al₂O₃ (C12A7) nanocrystals with the grain size of 360 nm have been fabricated by chemical co-precipitation method. Up-converted emissions at 367, 457, 476, 648, and 682 nm, corresponding to the ¹D₂ → ³H₆, ¹D₂ → ³F₄, ¹G₄ → ³H₆, ¹G₄ → ³F₄, and ³F₃ → ³H₆ transitions, respectively, are observed under 808 nm excitation. Plasmon-enhanced ultraviolet (UV) and blue upconverted emissions of Tm³⁺-doped C12A7 nanocrystals have been achieved by attaching Ag nanoparticles onto the surface of nanocrystals. The enhancement of the upconverted emissions is highly wavelength-dependent. The emission intensities of the sample with Ag⁺ concentration of 5.0 × 10⁻³ mol/L at 367 and 476 nm are enhanced about 10 and 3 times, respectively, relative to the sample without Ag attachment. The enhancement mechanism can be ascribed to surface plasmon resonance due to the highly localized electric field and the increased radiative decay rate around Ag nanoparticles. Our results suggest that Tm³⁺-doped C12A7 nanocrystals by attaching Ag nanoparticles might be a potential material for upconversion, compact and tunable short-wavelength lasers.