Ultraviolet-blue upconversion (UC) radiations of ${\mathrm{Ho}}^{3+}$ ions at 240, 290, 360, 385, 418, 445, $485\mathrm{nm}$ were observed in hexagonal $\mathrm{Na}\mathrm{Y}{\mathrm{F}}_4:{\mathrm{Yb}}^{3+}∕{\mathrm{Ho}}^{3+}$ powders under diode laser excitation of $970\mathrm{nm}$ . UC mechanism analyses illustrate that successive energy transfers from ${\mathrm{Yb}}^{3+}$ to ${\mathrm{Ho}}^{3+}$ generate emissions at 240, 360, 385, and $418\mathrm{nm}$ , while cross relaxations between ${\mathrm{Ho}}^{3+}$ ions evoke UC emissions at 290 and $445\mathrm{nm}$ . Power dependence analyses indicate that these UC emissions already have intense saturation effects even at low-power density range of $0.3–38\mathrm{W}∕{\mathrm{cm}}^2$ . Theoretical calculations based on steady-state equations demonstrate the proposed UC mechanisms and explain well the observed saturation effects.