Mechanism of quantum dot luminescence excitation within implanted SiO2:Si:C films

Abstract

Results of the investigation of photoluminescence (PL) mechanisms for silicon dioxide films implanted with ions of silicon (100 keV; 7 × 1016 cm−2) and carbon (50 keV; 7 × 1015–1.5 × 1017 cm−2) are presented. The spectral, kinetic and thermal activation properties of the quantum dots (Si, C and SiC) formed by a subsequent annealing were studied by means of time-resolved luminescence spectroscopy under selective synchrotron radiation excitation. Independent quantum dot PL excitation channels involving energy transfer from the SiO2 matrix point defects and excitons were discovered. A resonant mechanism of the energy transfer from the matrix point defects (E′ and ODC) is shown to provide the fastest PL decay of nanosecond order. The critical distances (6–9 nm) of energy transport between the bulk defects and nanoclusters were determined in terms of the Inokuti–Hirayama model. An exchange interaction mechanism is realized between the surface defects (Es′-centres) and the luminescent nanoparticles. The peculiarities of an anomalous PL temperature dependence are explained in terms of a nonradiative energy transfer from the matrix excitons. It is established that resonant transfer to the luminescence centre triplet state is realized in the case of self-trapped excitons. In contrast, the PL excitation via free excitons includes the stages of energy transfer to the singlet state, thermally activated singlet–triplet conversion and radiative recombination.