[en] Tin oxide (SnO_2) nanocrystals (NCs) based phosphor were synthesized by a green chemistry microwave-assisted hydrothermal method at different reactor pressures. The x-ray diffraction analysis showed that a single rutile SnO_2 phase with a tetragonal lattice structure was formed. The photoluminescence emission was measured for He–Cd laser excitation at 325 nm and it showed a broad band emission from 400 to 800 nm for all the synthesized reactor pressures. The broad emission spectra were due to the creation of various oxygen and tin defects as confirmed by x-ray photoelectron spectroscopy data. The origin of the emission in the SnO_2 NCs is discussed with the help of an energy band diagram. Analysis suggests that the visible emission of SnO_2 NCs is due to a transition of an electron from a level close to the conduction band edge to a deeply trapped hole in the SnO_2 NCs. The NCs were found to be suitable for warm near white light emission device applications. (paper)