Room-temperature ultraviolet emission of ${\mathrm{Tm}}^{3+}$ ions at 298 $({}^{1}I_6\to {}^{3}H_6)$ , 364 $({}^{1}D_2\to {}^{3}H_6)$ , and 391 nm $({}^{1}I_6\to {}^{3}H_5)$ was obtained in ${\mathrm{Y}}_2{\mathrm{O}}_3:{\mathrm{Yb}}^{3+}\text{–}{\mathrm{Tm}}^{3+}$ by continuous-wave diode laser excitation of $980\mathrm{nm}$ . Power dependence analysis demonstrates that five- and six-photon upconversion processes populate the ${}^{1}D_2$ and ${}^{1}I_6$ states, respectively. We believe that the ${}^{1}D_2$ population originates from the cross relaxation ${}^{1}G_4+{}^{3}F_4\to {}^{3}H_4+{}^{1}D_2$ of the ${\mathrm{Tm}}^{3+}$ ions, while subsequent energy transfer from ${\mathrm{Yb}}^{3+}$ to ${\mathrm{Tm}}^{3+}$ excites the ${}^{1}D_2$ state to the upper ${}^{1}I_6$ state. High multiphoton-induced ultraviolet emission is also expected for other trivalent rare-earth ions similar to ${\mathrm{Tm}}^{3+}$ .