Nanodiamond holds great interest in a variety of optical applications, the properties being correlated with surface modification, and the presence of both impurities and defects (contained either on their surface or within the crystal structure). Undecyl-nanodiamond produced by attachment of 1-undecene onto the nanodiamond surface could be a good candidate as a luminescent marker in the future; therefore, understanding of its optical properties is essential. In this work, the optical properties of the acid-purified nanodiamond and undecyl-nanodiamond were characterised using surface enhanced Raman spectroscopy (SERS) and photoluminescence spectroscopy. The results demonstrate that the characteristic diamond Raman signal at 1330 cm-1 was still observed after chemical surface modification, while the signal at ∼1600 cm-1 (attributed to graphite bands) disappeared after the modification. Broad photoluminescence emission is detected in the range 1.5-2.5 eV (500-800 nm), as typically found for isolated nanodiamond; these emission bands became narrower with attachment of 1-undecene as compared to the sample without surface functionalisation. The observed emission could be related to structural disorder on the nanodiamond surface. The temperature dependence of the intensity, peak position and band widths of each sample has been characterised.

Immobilization of fluorescent nanoparticles on graphene is an important step in the assembly of certain graphene-based photonic devices as well as in optical visualization of graphene and its defects. Hereby we report a viable approach to deposit diamond nanoparticles on a wide-area graphene substrate. It is demonstrated that a suitable plasma treatment leads to a selective immobilization of deposited nanodiamond on graphene with practically no agglomeration. Absence of photoemission from the individual adsorbed diamond nanoparticles suggests an energy transfer from the excited N-V centers to graphene.

Synergistic compositions of detonation nanodiamond (ND) particles in the form of 100nm aggregates in combination with molybdenum dialkyldithiophosphate were used as additives to 10W40 oils. Ring-on-disk tribological tests were performed under high load conditions using friction pairs with different hardnesses, namely normalized-normalized (“soft/soft”) and normalized-quenched (“soft/hard”) steel samples. For the “soft/hard” steel friction pair NDs provide significant reduction in both the coefficient of friction and wear as well as demonstrate polishing. For the “soft/soft” steel friction pair, however, no difference in the coefficients of friction was observed when the base oil was used with or without ND. In the test with oil containing the ND additive, the wear scar in the disk was wider, but more shallow, than in the test with pure oil. Current tests indicate that the significance of the reduction of friction and wear of the sliding surfaces in the presence of the ND additive in oil strongly depends on the hardness of the friction surfaces and most probably is connected with ND polishing effect.