We study transient photoluminescence (PL) in In0.2Ga0.8N nano-disks (NDs) fabricated from a 2 or 3 nm-thick quantum well (QW) by damage-free neutral-beam etching utilizing bio-nano-engineered etching templates. A lateral averaged diameter of the ND was controlled to be 9 nm with a high sheet-density up to 2.6×1011 cm-2. Transient PL in the NDs was measured as a function of temperature and compared with that in the mother QWs. Thermal quenching of PL is strongly suppressed in the NDs, while the PL intensity in the QWs rapidly decreases with increasing temperature. A PL-decay time in the NDs is 0.1 ns at 6 K, which is significantly shorter than that of 3.5 ns in the QW. The temperature dependence of the PL decaying property shows that a radiative decay time of 0.1 ns in the NDs is almost constant for temperature, while a non-radiative one decreases with increasing temperature. This significantly faster and relatively temperature-insensitive radiative decay time can be attribute to the strong confinement due to the ND formation in addition to strain relaxation.