A method of fabricating one or more colour centres in a crystal is described. The method comprises focusing a laser into a crystal to induce the creation, modification, or diffusion of defects within a focal region of the laser. Fluorescence detection is used to determine when one or more colour centres are formed within the focal region and the laser is terminated when a desired number of colour centres have been formed. The method enables colour centres to be formed in a crystal with a high degree of control in terms of both the number and location of colour centres within the crystal, and a degree of control over other parameters such as colour centre orientation and local environment. In particular, it is possible to form a well-defined pattern of colour centres within a crystal.

Method and systems are presented for authentication of precious stones, according to their natural ID and/or predetermined markings created in the stones, based on unique characteristic radiation response of the stone to predetermined primary radiation.

A diamond powder comprising diamond particles having an average particle size of no more than 20 μm and a vacancy or impurity-vacancy point defect concentration of at least 1 ppm. At least 70% of the volume of diamond in the powder is formed from a single crystal growth sector. This leads to a substantially uniform concentration of vacancies or impurity-vacancy point defects in the diamond particles because the rate of impurity take-up during growth is heavily dependent on the growth sector, which in turn leads to a more uniform fluorescent response. There is also described a method for making such a powder.

A diamond powder comprising diamond particles having an average particle size of no more than 20 μm and a vacancy or impurity-vacancy point defect concentration of at least 1 ppm. At least 70% of the volume of diamond in the powder is formed from a single crystal growth sector. This leads to a substantially uniform concentration of vacancies or impurity-vacancy point defects in the diamond particles because the rate of impurity take-up during growth is heavily dependent on the growth sector, which in turn leads to a more uniform fluorescent response. There is also described a method for making such a powder.

An ink includes a boron-doped nanodiamond having a specific surface area of 110 m.sup.2/g or greater, and electrical conductivity at 20° C. of 5.0×10.sup.−3 S/cm or greater.

An ink includes a boron-doped nanodiamond having a specific surface area of 110 m.sup.2/g or greater, and electrical conductivity at 20° C. of 5.0×10.sup.−3 S/cm or greater.

Provided is a polyoxyalkylene-chain surface-modified nanodiamond that is excellent in safety during production and in productivity. A surface-modified nanodiamond according to the present invention includes a nanodiamond particle and a surface-modifying group having a polyoxyalkylene chain and a silicon atom, the surface-modifying group surface-modifying the nanodiamond particle. A nanodiamond dispersion composition according to the present invention includes a dispersion medium and the surface-modified nanodiamond dispersed in the dispersion medium.

Provided is a polyoxyalkylene-chain surface-modified nanodiamond that is excellent in safety during production and in productivity. A surface-modified nanodiamond according to the present invention includes a nanodiamond particle and a surface-modifying group having a polyoxyalkylene chain and a silicon atom, the surface-modifying group surface-modifying the nanodiamond particle. A nanodiamond dispersion composition according to the present invention includes a dispersion medium and the surface-modified nanodiamond dispersed in the dispersion medium.

Disclosed are methods of purifying nanodiamonds and a method of making essentially pure nanodiamonds each involving mixing nanodiamonds with at least one salt to form a mixture; heating the mixture at a temperature from 200° C. to 1,000° C. for a time from 10 minutes to 10 hours; and combining a liquid with the heated mixture and centrifuging at a speed of 30 rcf to 25,000 rcf for a time from 10 seconds to 60 minutes to provide purified nanodiamonds. With the methods of the invention, pure NDs can be produced by one-step processing after air oxidation, without the need for any further centrifugation acts. Furthermore, the developed salt-assisted air oxidation method enables facile scale-up manufacturing of clean NDs, with a rounded shape transformed from original shard-like shape, which is impossible to achieve using any existing purification method.

Disclosed are methods of purifying nanodiamonds and a method of making essentially pure nanodiamonds each involving mixing nanodiamonds with at least one salt to form a mixture; heating the mixture at a temperature from 200° C. to 1,000° C. for a time from 10 minutes to 10 hours; and combining a liquid with the heated mixture and centrifuging at a speed of 30 rcf to 25,000 rcf for a time from 10 seconds to 60 minutes to provide purified nanodiamonds. With the methods of the invention, pure NDs can be produced by one-step processing after air oxidation, without the need for any further centrifugation acts. Furthermore, the developed salt-assisted air oxidation method enables facile scale-up manufacturing of clean NDs, with a rounded shape transformed from original shard-like shape, which is impossible to achieve using any existing purification method.