Patent ID: 7731795

Claim:
A method for making rhombohedral fluoroberyllium borate crystals having the formula MBe 2 BO 3 F 2 (MBBF) wherein M is Rb, Cs, or Tl, comprising the steps of: providing microcrystalline MBe 2 BO 3 F 2 powder, wherein M is Rb, Cs, Tl; and recrystallizing the microcrystalline MBe 2 BO 3 F 2 in an aqueous solution at a temperature of from about 300° C. to about 600° C. and at a pressure of from about 4 kpsi to about 30 kpsi, the aqueous solution comprising fluoride ions at a concentration of from about 1×10 −6 to about 5 molarity.