Abstract
Bright emission from fluorescent nanodiamonds (FNDs) is highly desirable for optical bio-imaging applications. Here we report about optimized ion-irradiation and heat treatment conditions for efficient creation of Nitrogen-vacancy (NV) centers in high pressure high temperature (HPHT) grown type Ib Nanodiamond samples irradiated in energy range (20-50 KeV) and at varying fluence (1012-1016 ions/cm2). Different low energy ion irradiations are not detrimental for the crystallinity of nanodiamonds as confirmed by X-ray diffraction and HRTEM. The concentration of defects near the outer surface (non-diamond carbon) has been increased for highest ion dose (50 KeV, 1016 ions/cm2) as compared to lower ion dose (50 KeV, 1013 ions/cm2). The relative emission intensity of characteristic Zero-phonon lines of NV°, NV- centers as compared to broad emission in the range 550-750 nm was monitored with varying NV creation conditions. Sample irradiated at 50 KeV and with fluence of 1013 ions/cm2 show maximum emission in the phonon side band (550-750 nm) with maxima at 680 nm. These optimized ion irradiation conditions leads to the fabrication of 12.5±0.8 ppm concentration of NV- centers in nanodiamonds. This is desirable for their use as biomarker. This work provides a recipe for creating bright nanodiamonds for optical imaging applications.
Highlights
Fluorescent nano particles (FNPs) are highly desirable for optical bio-imaging applications.[1,2] Bio-imaging demands higher photo-stability and bio-compatibility as compared to organic fluorophores and semiconductor quantum dots
The emission of fluorescent marker should be in the range of near infrared (NIR) wavelengths so that it does not overlap with epifluorescence of cells and tissues
We have explored the effect of ion beam energy (20, 30 & 50 KeV) and ion-dose (1012, 1013, 1014, 1015& 1016 ions/cm2) for efficient creation of bright fluorescent Nano diamonds (NDs)
Summary
Fluorescent nano particles (FNPs) are highly desirable for optical bio-imaging applications.[1,2] Bio-imaging demands higher photo-stability and bio-compatibility as compared to organic fluorophores and semiconductor quantum dots. We have explored the effect of ion beam energy (20, 30 & 50 KeV) and ion-dose (1012, 1013, 1014, 1015& 1016 ions/cm2) for efficient creation of bright fluorescent NDs. The optimum conditions for creation of nitrogen-vacancy centers in NDs have been established with minimum structural modification to harness maximum emission in the phonon side band: a highly desirable property for their application for bio-imaging applications. We report optimum processing conditions for NV center fabrication for optical bio-imaging and two-photon excitation spectroscopy, where large concentration of NV color centers near the surface of NDs is required
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