  Herein, we report on the improvement of structural quality and enhancement of
photoluminescence (PL) emission for an optimally N doped nanocrystalline
diamond (NCD) film. Pure and N doped nanocrystalline diamond films are
synthesized on Si by hot filament chemical vapour deposition using NH3:CH4:H2
at different nominal N/C ratios viz. 0, 0.13, 0.35, 0.50 and 0.75 in feedstock.
X ray diffraction analysis reveal a systematic initial increase and then a
decrease in crystallite size with N/C ratio in feedstock. Further, a monotonic
increase in Raman line width and peak position of diamond band indicates that
the compressive strain in diamond lattice increases as a function of N/C ratio
upto 0.50. However, at higher N/C ratio of 0.75, the compressive strain gets
relaxed a little and produces a lower strain. Furthermore, a unique Raman mode
at 1195 cm-1 is observed corresponding to the C=N-H vibrations indicating a
significant N concentration in the NCD films. In addition, visible and UV PL
studies reveal the presence of several N related color centres with multiple
emission lines in the range of 380 to 700 nm. An optimally N doped diamond film
grown at N/C ratio of 0.35 in feedstock shows a significant enhancement in room
temperature PL emission at about 505 and 700 nm. This PL enhancement is
attributed to H3 and other aggregates of N related defect centres, under 355
and 532 nm laser excitations respectively.
