A method for passivating crystal defects of a nonlinear optical crystal, comprising: growing a nonlinear optical crystal in the presence of at least one of fluorine, a fluoride ion and a fluoride-containing compound; mechanically preparing the nonlinear optical crystal; monitoring a degree of passivation of the NLO crystal via one or more selected absorption bands; performing an annealing process on the nonlinear optical crystal, wherein the performing an annealing process on the NLO crystal comprises: maintaining the nonlinear optical crystal at a selected temperature in the range of 300°C to 350°C; maintaining a low humidity, low oxygen environment during the annealing process; and exposing the nonlinear optical crystal to a passivating gas; wherein the growing a nonlinear optical crystal in the presence of at least one of fluorine, a fluoride ion and a fluoride-containing molecule comprises: (a) growing a nonlinear optical crystal including one or more borate-based compounds in the presence of at least one of fluorine, a fluoride ion and a fluoride containing molecule; or (b) growing a nonlinear optical crystal including one or more borate-based compounds in the presence of at least one of fluorine, a fluoride ion and a fluoride containing molecule; and wherein the growing a nonlinear optical crystal including one or more borate-based compounds in the presence of at least one of fluorine, a fluoride ion and a fluoride-containing molecule comprises: growing a nonlinear optical crystal including at least one of Beta-Barium Borate, Lithium Triborate, Lithium Tetraborate, Cesium Lithium Borate (CLBO) and Cesium Borate in the presence of at least one of fluorine, a fluoride ion and a fluoride-containing molecule. growing a nonlinear optical crystal in the presence of at least one of fluorine, a fluoride ion and a fluoride-containing compound; mechanically preparing the nonlinear optical crystal; monitoring a degree of passivation of the NLO crystal via one or more selected absorption bands; performing an annealing process on the nonlinear optical crystal, wherein the performing an annealing process on the NLO crystal comprises: maintaining the nonlinear optical crystal at a selected temperature in the range of 300°C to 350°C; maintaining a low humidity, low oxygen environment during the annealing process; and maintaining the nonlinear optical crystal at a selected temperature in the range of 300°C to 350°C; maintaining a low humidity, low oxygen environment during the annealing process; and exposing the nonlinear optical crystal to a passivating gas; wherein the growing a nonlinear optical crystal in the presence of at least one of fluorine, a fluoride ion and a fluoride-containing molecule comprises: (a) growing a nonlinear optical crystal including one or more borate-based compounds in the presence of at least one of fluorine, a fluoride ion and a fluoride containing molecule; or (b) growing a nonlinear optical crystal including one or more borate-based compounds in the presence of at least one of fluorine, a fluoride ion and a fluoride containing molecule; and wherein the growing a nonlinear optical crystal including one or more borate-based compounds in the presence of at least one of fluorine, a fluoride ion and a fluoride-containing molecule comprises: growing a nonlinear optical crystal including at least one of Beta-Barium Borate, Lithium Triborate, Lithium Tetraborate, Cesium Lithium Borate (CLBO) and Cesium Borate in the presence of at least one of fluorine, a fluoride ion and a fluoride-containing molecule. (a) growing a nonlinear optical crystal including one or more borate-based compounds in the presence of at least one of fluorine, a fluoride ion and a fluoride containing molecule; or (b) growing a nonlinear optical crystal including one or more borate-based compounds in the presence of at least one of fluorine, a fluoride ion and a fluoride containing molecule; and wherein the growing a nonlinear optical crystal including one or more borate-based compounds in the presence of at least one of fluorine, a fluoride ion and a fluoride-containing molecule comprises: growing a nonlinear optical crystal including at least one of Beta-Barium Borate, Lithium Triborate, Lithium Tetraborate, Cesium Lithium Borate (CLBO) and Cesium Borate in the presence of at least one of fluorine, a fluoride ion and a fluoride-containing molecule.