Enhancing the upconversion luminescence and photothermal conversion properties of ∼800nm excitable core/shell...

Upconversion nanoparticles capable of strongly absorbing photons in a wide spectral range are highly desired for practical applications. In this work, IR-806 dye was used to increase the light absorptivity of Nd³⁺/Yb³⁺/Er³⁺ tri-doped core/shell nanoparticles and then to enhance their upconversion luminescence under ∼800nm excitation. The IR-806 dye exhibited more efficient energy transfer to Nd³⁺ ions than to Yb³⁺ ions for subsequent upconversion emission due to the increased spectral overlap between the dye emission and Nd³⁺ absorption. The influence of the Nd³⁺ concentration in the shell and the dye/nanoparticle ratio on the dye-sensitization effect was also investigated. A maximum 28-fold overall enhancement in the emission intensity was achieved for NaYF₄:Yb³⁺/Er³⁺@NaYF₄:Yb³⁺/Nd³⁺ core/shell nanoparticles using dye sensitization. The dye-sensitized NaYF₄:Yb³⁺/Er³⁺@NaYF₄:Yb³⁺/Nd³⁺ core/shell nanoparticles also exhibited increased photothermal conversion capabilities and excellent temperature sensing properties, enabling their potential application in photothermal nanoheaters with real-time temperature monitoring under 808nm single beam excitation.