Method for reducing defect concentration in crystals

A method for removing one or more defects and/or relieving strain in a non-diamond crystal, the method comprising the steps of:

• placing at least one non-diamond crystal in a sealable vessel or capsule;
• adding a substance to the sealable vessel or capsule that is capable of transforming to a supercritical fluid under pre-determined process conditions;
• sealing the sealable vessel or capsule;
• heating the sealable vessel or capsule to pre-determined process conditions, including a temperature above about 550 degrees Celsius and a pressure between about 0.2 GPa and about 8 GPa, wherein the substance becomes a supercritical fluid at said pre-determined process conditions and surrounds the at least one non-diamond crystal, and maintaining the at least one non-diamond crystal at the pre-determined process conditions for a sufficient amount of time to remove one or more defects and/or relieve strain in the at least one non-diamond crystal;
• and
• removing at least one improved non-diamond crystal from the sealable vessel or capsule.