LaF3 nanocrystals (NCs) are usually used as good host matrix for down-conversion phosphors owing to their impressive photophysical properties. In this study, Pr3+-activated LaF3 with hollow hexagon nanostructures (HHNs) is achieved by a green and eco-friendly hydrothermal method without any catalyst, template, or surfactant. The pore structure of the LaF3 HHNs is greatly affected by the content of Pr3+ ions and hydrothermal reaction time. The LaF3: Pr3+ NCs excited by 467nm light show strong emission peaks locating in visible light region (centered at 612 and 635nm) and the first biological window region (existed in 689 and 721nm), respectively. The relative photoluminescence (PL) intensity of LaF3: Pr3+ NCs from 20 to 60 degrees C (biological temperature) decreases slightly and decreases only 20% at 120 degrees C. The PL emission intensity could reach the maximal value with doping 1.5% Pr3+ ions. Based on the outstanding photophysical properties, LaF3: Pr3+ NCs will be used for both warm white light-emitting diodes and bio-imaging.