Heat treatment of nanodiamond particles with controlled powder layer depth
Luminescent diamond is made by creating vacancies in diamond grains and heat treating the diamond grains by controlling a thickness of the diamond grains on a substrate. The heat treatment may occur in a temperature range that does not burn the diamond grains, and the controlled thickness produces an even color change and/or promotes oxygen terminations on the diamond particle surfaces.
1 . A method of making luminescent diamond consisting of:
subjecting a volume of precursor diamond grains to high-pressure/high-temperature conditions in a pressure cell and thereby forming diamond grains with luminescent centers, wherein the high-pressure/high-temperature conditions are from about 1300° C. to about 2500° C. and from about 3.0 GPa to about 10 GPa;
forming a suspension by suspending the diamond grains in a liquid;
adhering the suspension to a substrate and controlling a thickness of the suspension on the substrate;
heat treating the suspension on the substrate at a temperature not exceeding 650° C., thereby changing oxygen terminations on diamond particles of the suspension and increasing a photoluminescence intensity of the diamond grains; and
removing the diamond particles from the substrate and separating the removed diamond particles by grain size.
2 . The method of claim 1 , wherein the luminescent centers include at least one of nitrogen or silicon vacancies.
3 . The method of claim 1 , wherein the liquid includes water.
4 . The method of claim 3 , wherein the liquid includes a surface tension suppressant.
5 . The method of claim 4 , wherein the surface tension suppressant includes alcohol.
6 . The method of claim 1 , wherein the liquid is 10% to 100% alcohol by weight.
7 . The method of claim 1 , wherein the substrate is glass.
8 . The method of claim 1 , wherein the thickness is controlled to be less than 30 μm.
9 . The method of claim 8 , wherein the thickness is controlled to be less than 25 μm.
10 . The method of claim 8 , wherein the thickness is controlled to be between 1 μm and 15 μm.
11 . The method of claim 1 , wherein controlling the thickness includes removing material that exceeds a threshold thickness.
12 . The method of claim 1 , wherein adhering the suspension to the substrate includes drying the suspension.
13 . The method of claim 12 , wherein drying the suspension is performed at a temperature below a boiling point of the liquid and before heat treating the suspension.
14 . The method of claim 1 , wherein adhering the suspension to the substrate includes coating the suspension on the substrate using one or more of dip coating, spin coating, dry coating, or slip casting.
15 . The method of claim 1 , wherein heat treating the suspension includes heat treating at a temperature not exceeding 600° C.
16 . The method of claim 1 , wherein heat treating the suspension includes heat treating at a temperature not exceeding 550° C.
17 . The method of claim 1 , wherein heat treating the suspension is performed for a duration of up to two hours.
18 . The method of claim 1 , wherein heat treating the suspension is performed for a duration of between 30 minutes and 90 minutes.
19 . The method of claim 1 , wherein the pressure cell is configured to impose a differential or asymmetric pressure on the precursor diamond grains.
20 . The method of claim 1 , wherein:
the volume of precursor diamond grains is formed by consolidating and compacting a volume of pre-existing diamond grains; and
the volume of precursor diamond grains comprises intercrystalline diamond bonding.
21 . The method of claim 1 , wherein:
the volume of precursor diamond grains is formed by consolidating and compacting a volume of pre-existing diamond grains; and
the volume of precursor diamond grains does not comprise intercrystalline diamond bonding.
22 . A method of making luminescent diamond consisting of:
subjecting a volume of natural precursor diamond grains with an average grain size of from 10 μm to 50 μm to high-pressure/high-temperature conditions in a pressure cell and thereby forming diamond grains with luminescent centers, wherein the high-pressure/high-temperature conditions are from about 1300° C. to about 2500° C. and from about 3.0 GPa to about 10 GPa;
forming a suspension by separating the diamond grains into a powder and suspending the diamond grains in water;
adhering the suspension to a glass substrate and controlling a thickness of the suspension on the substrate to be from 5 μm to 15 μm, wherein the diamond grains have a concentration of from 0.1% to 10% by weight in the suspension;
heat treating the suspension on the substrate at a temperature in a range between 450° C. and 550° C. for 60 minutes, thereby changing at least one of a color of the suspension or oxygen terminations on diamond particles of the suspension and increasing a photoluminescence intensity of the diamond grains; and
removing the diamond particles from the substrate and separating the removed diamond particles by grain size,
wherein the pressure cell is configured to impose a differential or asymmetric pressure on the precursor diamond grains in order to plastically deform the precursor diamond grains and produce the luminescent centers in the diamond grains.