The past few years witnessed extensive emergence of short-wavelength upconversion(UC) emission stimulated photoactivation studies. However, low efficiency of multi-photon process greatly limits further applications. Here, ultraviolet(UV) upconversion emissions originated from multi-photon process of Tm~(3+) were studied with Nd~(3+)-sensitized NaGdF_4:Yb,Tm@NaYF_4:Nd,Yb core/shell nanoparticles. Crucial factors, including the contents of sensitizers Nd~(3+), Yb~(3+) and activator Tm~(3+), as well as the excitation power density were investigated based on the UV emission. Spectral results showed that high contents of Nd~(3+) in shell region up to 50%(molar fraction hereafter) and Yb~(3+) of 10% were essential to mediate the energy transfer via the core/shell interface and facilitate multi-photon UV emissions. Compared with segregated activator and sensitizer, a core/shell strategy with isolated Nd~(3+) in the shell was important for higher UV emission. Although the upconverting process was initiated with Nd~(3+)→Yb~(3+), the short-wavelength emissions were intrinsically coming from four- and five-photon process. The optimized nanoparticles were found to be able to manipulate the configuration transition of azobenzene molecules, and it could be promising for near infrared(NIR) triggered optical switches applications. The past few years witnessed extensive emergence of short-wavelength upconversion (UC) emission stimulated photoactivation studies. However, low efficiency of multi-photon process greatly limiting further applications. Here, ultraviolet (UV) upconversion emissions originated from multi-photon process of Tm ~ (3+) were studied with Nd ~ (3 +) - sensitized NaGdF_4: Yb, Tm @ NaYF_4: Nd, Yb core / shell nanoparticles. Crucial factors, including the contents of sensitizers Nd ~ (3+), Yb ~ 3+) and activator Tm ~ (3+), as well as the excitation power density were investigated based on the UV emission. Spectral results showed that high content of Nd ~ (3+) in shell region up to 50% (molar fraction Hereafter) and Yb ~ (3+) of 10% were essential to mediate the energy transfer via the core / shell interface and to facilitate multi-photon UV emissions. Compared with segregated activator and sensitizer, a core / shell strategy with isolated Nd ~ ( 3+) in the shell was important for higher UV emission. Although the upconverting process was initiated with Nd ~ (3+) → Yb ~ (3+), the short-wavelength emissions were intrinsically coming from four- and five-photon processes. The optimized nanoparticles were found to be able to manipulate the configuration transition of azobenzene molecules , and it could be promising for near infrared (NIR) triggered optical switches applications.