Nanocomposites and nanomaterials
Luminescence study of samarium doped silicon oxide films formed by coevaporation technique

Michailovska K.V., Dan’ko V.А., Indutnyi I.Z., Shepeliavyi P.E., 
Sopinskyy M.V.
V. Lashkaryov Institute of Semiconductor Physics Natl. Acad. of Sci. of Ukraine. 45 Prospect Nauky, 03028 Kyiv, Ukraine.  
E-mail: danko-va@ukr.net

Structures containing ions of rare-earth elements and Si nanoparticles (nps-Si), which are promising for the creation of integrated light sources based on Si, are of great interest. In this work the photoluminescence (PL) properties of SiOx (x<2) films containing samarium (Sm) ions and nps-Si were studied. The samples were produced by thermal coevaporation in vacuum of silicon monoxide powder and metallic Sm onto c-Si substrates. Annealing the samples at different temperatures (Tan = 550-970°C) in air allowed the formation of nps-Si and optically active samarium centers. The Sm content in the samples varied from 0,8 to 2,0 wt %. We studied SiOx:Sm films and SiOx films without Sm. PL measurements at room temperature were carried out under excitation by diode laser radiation with a wavelength of 405 nm.
No photoluminescence of Sm ions was observed in films doped with 0.8 wt% Sm, and only emission of nps-Si was observed. The PL studies of the films annealed at Tan = 550-750°C have shown that the integral luminescence spectrum, associated with amorphous nps-Si in SiOx:Sm films, is more than twice that for SiOx films without Sm. Annealing of these SiOx:Sm films at 970° C led to the formation of crystalline nps-Si, which is confirmed by the appearance of a PL band with a peak at about 820–840 nm. Unlike the SiOx:Sm in Sm-free SiOx films, annealed at 970°C, the PL band with a peak at 820-840 nm appears only after passivation of dangling bonds of silicon atoms at the nps-Si─SiOx interface (annealing in hydrogen, etching in HF, etc). We assume that Sm atoms modify the surface of nps-Si formed in the SiOx matrix during annealing. Passivation of nps-Si occurs due to the formation of Si-O-Sm bonds in the suboxide shell surrounding the Si nanoparticles. A possible mechanism of nps-Si passivation is discussed.
The spectra of SiOx: Sm films with a content of 2 wt% Sm consist of rather sharp PL lines at 640, 660, and 725 nm. The energy position of these lines is in good agreement with the energies of transitions between levels in Sm 3+ ions. But the nps-Si luminescence in these samples is very attenuated. These decrease in the PL intensity of the nps-Si is explained by the transfer of energy from nps-Si sensitizers to samarium ions located close to them.