Photoluminescence of Amorphous Hydrogenated Carbon Films, a-C:H

Abstract

Results are presented on the photoluminescence of plasma deposited amorphous carbon (a-C:H) films. Emission and exci tation spectra anti-Stokes emission, PL decay and fatigue, T-dependence of PL and photobleaching were mesuared. The data are discussed in terms of radiative recombination of the strongly localized electron-hole pairs.As recently shown, in amorphous hydrogenated carbon films (a-C:H) powerful talls of localized states occur in the mobility gap that are due to a high degree of structural disorder [1] while a radiative recombination in this material is highly efficient [2, 3]. These properties, in our view, make a-C:H suitable for verification of models of recombination kinetics of photoexcited charge carriers in highly disordered systems with the use of photoluminescence (PL).

π-bonded clusters in amorphous carbon materials

“…Excitation of a-C : H by band edge photons will tend to create an electron and hole in the same cluster where they will remain bound by the surrounding sp3 barrier. This binding favours intracluster radiative recombination, giving luminescence in a-C : H and carbon-rich a-Si, -xCx : H which is efficient and largely independent of temperature and electric field, as observed previously (Lin and Feldman 1982, Siebert, Carius, Fuhs and Jahn 1987, Liedkte et al 1989, Vassilyev et al 1989. In contrast, luminescence in a-Si : H and siliconrich a-Si, -&: H is strongly quenched at moderate temperatures (Siebert et al 1987, Vassilyev et al 1989.…”

“…This binding favours intracluster radiative recombination, giving luminescence in a-C : H and carbon-rich a-Si, -xCx : H which is efficient and largely independent of temperature and electric field, as observed previously (Lin and Feldman 1982, Siebert, Carius, Fuhs and Jahn 1987, Liedkte et al 1989, Vassilyev et al 1989. In contrast, luminescence in a-Si : H and siliconrich a-Si, -&: H is strongly quenched at moderate temperatures (Siebert et al 1987, Vassilyev et al 1989. Liedtke et al (1989) noted that recombination rates in carbon-rich a-Si, -,C,:H alloys do not correlate with the defect density, as they do in The presence of localized states above the optical band edges in a-C : H allows luminescence to occur above its optical gap.…”

Diffusive Spectra of Antistokes Wing of Photoluminescence of Carbon Nanostructures

“…Relatively recently [1][2][3][4][5][6], interesting features of the photoluminescence (PL) of carbon quantum dots (CQD) were discovered: the wide structureless band in the visible spectral region, the half width, the photon energy at the band maximum, and whose shortwave edge depend on the energy of the excitation quantum. Similar features of PL were observed previously in such carboncontaining objects as amorphous hydrogenated α-C: H carbon [7] and native biopolymer-collagen [8]. An additional feature of the PL spectra of α-C: H and collagen was the observation of anti-Stokes radiation (ASR) at temperatures above the temperature of liquid nitrogen.…”

Photoluminescence of Amorphous Multilayer Structures a-C:H/a-Si:H

“…1, films 1 , 2 ). Such a quenching of the photoluminescence with an increase in the temperature was observed by Vasil'ev et al [2] at temperatures T > 350 K and T > 620 K. In the films characterized by photon energies h ν max ≅ 2.9 eV, the intensity of photoluminescence is independent of the temperature in the range 4.2-900 K. The decrease in the intensity of photoluminescence with an increase in the temperature is associated with the thermal effusion of hydrogen. The content of hydrogen in the films for which the maximum of the photoluminescence intensity corresponds to photon energies h ν max ≅ 2.05-2.2 eV was estimated from the infrared absorption spectra and amounted to 25-30%.…”