## 1 Introduction  
Following the early studies on porous silicon photoluminescence (PL) [1], optical properties of silicon nanocrystals (Si NCs) in solid matrices have been a focus of thorough research. Bright luminescence at room temperature from Si NCs, not observable for bulk silicon, appears very intriguing from the point of view of optoelectronic applications [2]. Different host matrices for Si NCs such as silicon oxide, nitride, and carbide are examined [3; 4; 5], while the most intense luminescence is typically observed for Si NCs in SiO\({}_{2}\) matrix due to the smallest concentration of PL quenching centers [6]. At the same time, enhanced electron transport properties of Si NCs array in matrices with lower band gap (silicon nitride or carbide) are preferable for the photovoltaic applications [4]. To achieve a precise control of the size of Si NCs multilayered thin films can be fabricated using so-called superlattice(SL) approach [7; 8; 9]. This approach allows one to limit the maximum size of Si NCs by deposition of Si-rich layers, wherein Si NCs are self-organized during high temperature annealing, alternating with stoichiometric barrier layers, which should remain unchanged [9; 10]. However, as shown recently, the stability of multilayers against annealing depends on the thickness of layers and treatment temperature, thus partial or total intermixing of layered structure may occur, and Si NCs with the size exceeding the thickness of initial of Si-rich layers may be formed [11; 12].  
The question about the origin of observed luminescence is especially complicated in the case of silicon nitride-based superlattices, since a large number of radiative defects are found in SiN\({}_{\mathrm{x}}\) films, such as \(N_{\mathrm{4}}\)\({}^{+}\), \(N_{\mathrm{2}}\)\({}^{0}\) or K-centers [6; 13]. PL maximum attributed to Si NCs in Si\({}_{3}\)N\({}_{\mathrm{4}}\) matrix is detected in a broad range of photon energies, generally from 1.5 to 3 eV [4; 9; 13; 14; 15]. One of the main arguments in favor of quantum confinement effect, which is responsible for such PL, is a blue shift of peak energy with decreasing Si NCs size. At the same time, similar PL spectra are observed for SiN\({}_{\mathrm{x}}\) films without Si NCs, whereas corresponding PL peak might be shifted in a wide range from about 1.6 to 2.6 eV by changing Si/N ratio [16; 17]. A characteristic lifetime of such defect-related PL is of order of nanoseconds [18], while Si NC-related PL is known to possess much longer decay times in a microsecond range [3; 12]. Hence, time-resolved PL measurements are important for the correct identification of PL source, which are often not presented in papers dedicated to Si NC luminescence in Si\({}_{3}\)N\({}_{\mathrm{4}}\)[9; 10; 13].  
In the present study we demonstrate the formation of silicon nitride-embedded Si NCs, which emit in near-IR region (peak at 1.3-1.4 eV) with a characteristic PL lifetime in a microsecond timescale. In this spectral region, no contribution from radiative defects is expected. Similar near-IR luminescence with the peaks in the range 1.4-1.7 eV was shown recently from annealed B-doped SiN\({}_{\mathrm{x}}\)/Si\({}_{3}\)N\({}_{\mathrm{4}}\) multilayer films with Si quantum dots produced by magnetron sputtering; however, no time-resolved PL data were provided [10].