• PDF / 696,013 Bytes
• 7 Pages / 612 x 792 pts (letter) Page_size
• 96 Downloads / 284 Views

DOWNLOAD

REPORT

---

Optical Properties of Carbon Nanoparticles Nikolay N. Melnik P.N.Lebedev Physical Institute RAS, Moscow, Russian Federation ABSTRACT Samples of carbon nanoparticles obtained by different technologies (carbon plasma deposition, irradiation, anodic etching etc.). by Raman scattering and photoluminescence were studied. It was shown that there are carbon nanoparticles which consist of a core containing sp2 bonds and a shell containing sp3 bonds. These particles have a rather intense photoluminescence. We propose the following photoluminescence mechanism of such nanoparticles: first the nanoparticle core absorbs light; further excitation is transmitted to the external cover or environment where photorecombination occurs. This effect occurs when the size of the particles becomes smaller than the size of the wave function excited state of the nanoparticle. The aim of this research is to check this mechanism. INTRODUCTION It is known that some samples of disordering carbon have a strong photoluminescence in the visible region of spectrum. Such photoluminescence has other nature than a photoluminescence of diamonds which arise because of impurity and defects. This work is devoted to questions which are not much discussed in the literature - a disordered carbon luminescence EXPERIMENT AND DISCUSSION Raman (RS) and photoluminescence (PL) spectra were recorded on a U-1000 spectrometer with micro-Raman attachment at room temperature. Low-power excitation light (488 nm, a transparent region) with the spatial resolution ~20 microns. It is obvious, that the dark region of a film represents carbon with structure of disorder crystalline graphite. In accordance with decreasing of the graphite nanoparticles sizes (that is visible on shifting and broadening of RS bands, especially for sp3 band ~ 1360cm-1), the increasing of photoluminescence intensity occurs. Note that curve 1 in Fig. 2b almost coincides with curve 5 in Fig. 3a (same as curve 2 in Fig. 1), although the samples were prepared by cardinally different methods. We can assume that the intensive photoluminescence is determined by availability graphite nanoparticles. Photoluminescence spectra of the irradiated diamond In the beginning of an irradiation (at small doses) the carbon particles with graphite structure surrounded with diamond structure carbon arise inside of a diamond crystal [4]. The amount of such particles is incremented with magnification of a radiation dose. The structure of these particles is similar to the structure of carbon particles which we consider. On the basis of the suggested mechanism it is possible to make the following assumption: the photoluminescence

Figure 4. a. - Change of diamond photoluminescence spectra, depending on the radiation exposure dose. b. - Change of a photoluminescence of the irradiated (He 350keV×5⋅1015cm-2) natural diamond with its own weak photoluminescence.

spectra of the irradiated diamond will be determined most likely by a spectrum of a photoluminescence of initial diamond. It is experimentally revealed that at small doze