Particle size significantly affects the brightness of luminescent nanocrystals. Herein we firstly adopt a 1530 nm CW laser as the optical heating source to increase the particle size of Er3+ heavily doped nanocrystals, leading to giant enhancement of the luminescent intensity. The advantages of this method are mainly feature along the facile route, with an ultrafast process, and low threshold of the laser power density. The detailed mechanisms of the laser annealing are carefully investigated. In addition, fluorescence intensity ratio behaviours using different emission bands are comparatively investigated.