Doping of carbon nanoparticles with impurity atoms is central to their application. However, doping has proven elusive for very small carbon nanoparticles because of their limited availability and a lack of fundamental understanding of impurity stability in such nanostructures. Here, we show that isolated diamond nanoparticles as small as 1.6 nm, comprising only ∼400 carbon atoms, are capable of housing stable photoluminescent colour centres, namely the silicon vacancy (SiV). Surprisingly, fluorescence from SiVs is stable over time, and few or only single colour centres are found per nanocrystal. We also observe size-dependent SiV emission supported by quantum-chemical simulation of SiV energy levels in small nanodiamonds. Our work opens the way to investigating the physics and chemistry of molecular-sized cubic carbon clusters and promises the application of ultrasmall non-perturbative fluorescent nanoparticles as markers in microscopy and sensing.

We report a ring-cavity thulium fiber laser mode locked with a single-wall carbon nanotube absorber used in transmission. A carboxymethyl cellulose polymer film with incorporated carbon nanotubes synthesized by the arc discharge method has an absorption coinciding with in the amplification bandwidth of a Tm-doped fiber. This laser is pumped by an erbium fiber laser at 1.57 microm wavelength and produces a 37 MHz train of mode-locked 1.32 ps pulses at 1.93 microm wavelength with an average output power of 3.4 mW.

t.v. kononenko 1,u m. meier 2 m.s. komlenok 1 s.m. pimenov 1 v. romano 2 v.p. pashinin 1 v.i. konov 1

Microstructure and its effect on field electron emission of grain-size-controlled nanocrystalline diamond films Ultrananocrystalline diamond ͑UNCD͒ films 0.1-2.4 m thick were conformally deposited on sharp single Si microtip emitters, using microwave CH 4 -Ar plasma-enhanced chemical vapor deposition in combination with a dielectrophoretic seeding process. Field-emission studies exhibited stable, extremely high ͑60-100 A/tip͒ emission current, with little variation in threshold fields as a function of film thickness or Si tip radius. The electron emission properties of high aspect ratio Si microtips, coated with diamond using the hot filament chemical vapor deposition ͑HFCVD͒ process were found to be very different from those of the UNCD-coated tips. For the HFCVD process, there is a strong dependence of the emission threshold on both the diamond coating thickness and Si tip radius. Quantum photoyield measurements of the UNCD films revealed that these films have an enhanced density of states within the bulk diamond band gap that is correlated with a reduction in the threshold field for electron emission. In addition, scanning tunneling microscopy studies indicate that the emission sites from UNCD films are related to minima or inflection points in the surface topography, and not to surface asperities. These data, in conjunction with tight binding pseudopotential calculations, indicate that grain boundaries play a critical role in the electron emission properties of UNCD films, such that these boundaries: ͑a͒ provide a conducting path from the substrate to the diamond-vacuum interface, ͑b͒ produce a geometric enhancement in the local electric field via internal structures, rather than surface topography, and ͑c͒ produce an enhancement in the local density of states within the bulk diamond band gap.

The formation and thermodynamic stability of silicon‐vacancy (Si‐V) color centers, intensively emitting at a wavelength of 738 nm, are demonstrated for the first time in nanodiamonds less than 10 nm in size. These findings open prospects for the production of stable and efficient optical nanoemitters (single‐photon emitters) based on nanodiamond.