[en] La₂O₂S:Yb,Pr nanometer phosphor have been prepared by a novel ethanol-assistant solution combustion (EASC) method in ethanol-water solution medium via a relatively mild and slow combustion process, using ethanol as preigniting fuel and inexpensive thioacetamide as sulfur-containing organic fuel. Investigation results show: ethanol preigniting serves the role of ignition combustion decomposition reaction between rare earth nitrate and organic fuel and promotes the formation of uniform and less agglomerative rare earth oxysulfide nanocrystals. Single phase Ln₂O₂S:Yb,Pr nanocrystals are obtained with appropriate ethanol/water ratio and further annealing at 1000 deg. C for 2 h in reduced atmosphere. The La₂O₂S:Yb,Pr nanocrystals exhibit an intense green emission assigned to the Pr³⁺ ions ³P₀ → ³H₄ transition and a broad near infrared (NIR) emission under 980 nm pump. The defects residing in La₂O₂S:Yb,Pr nanocrystals is the probable origins for the NIR emission. The annealing process makes the green emission improve and the NIR emission weaken. After annealing treatment at 1000 deg. C, the upconversion luminescence intensity is close to that of the bulk sample prepared by a solid-state reaction method