Nanocomposites and nanomaterials

Formation of molecular Se2 dimers 
in semiconductor nanocrystal-doped borosilicate glasses 
Azhniuk Yu.M.1,2, Lopushansky V.V.1, Gomonnai A.V.1,2, Zahn D.R.T.3 
1 Institute of Electron Physics, Ukr. Nat. Acad. Sci., 21 Universytetska Str., 88017 Uzhhorod, Ukraine. 
E-mail: yu.azhniuk@gmail.com
2 Uzhhorod National University, 46 Pidhirna Str., 88000 Uzhhorod, Ukraine.
3 Semiconductor Physics, Chemnitz University of Technology, D-09107 Chemnitz, Germany.
Our earlier measurements showed that in silicate glasses doped with II–VI semiconductor nanocrystals (NCs) Se2– molecular dimers can be formed under thermal treatment at 625 to 725 ºC along with diffusion-limited growth of the II–VI NCs [1]. Here we present Raman measurements for semiconductor NC-doped borosilicate glass decoloured by annealing for 1 h at 800 to 1000 ºC which make us revise our earlier vision of the conditions of formation of molecular Se2 dimers.
After rapid quenching, the decoloured samples were cut into pieces and subjected to thermal treatment at 625 to 725C (from 1 to 12 h). This resulted in the precipitation of semiconductor NCs as evidenced by optical absorption spectra.
Micro-Raman scattering measurements were performed for both decoloured glasses and glasses with semiconductor NCs using a Horiba LabRAM spectrometer or a Dilor XY 800 spectrometer with exc= 488.0 nm, 514.7 nm, or 632.8 nm.
Decolouring results in vanishing of II–VI NC phonon-related peaks in the Raman spectra. Meanwhile, for the decoloured glass samples where the Cd1‑yZnySe or CdSe1–xSx NCs in the initial samples contained a considerable amount of selenium (x and y below 0.5), narrow Raman peaks near 325 and 650 cm–1 are observed related to Se2– molecular dimers. It is clear from the spectra that Se2 dimers are formed in the borosilicate glass at the initial (high-temperature) annealing stage (at least within 800–1000 ºC range). This observation enables us to revise our earlier idea of the Se2 molecular dimers being formed in borosilicate glasses simultaneously with CdSe-rich NCs at much lower temperatures [1]. 

1.	Azhniuk Yu.M., Lopushansky V.V., Hutych Yu.I., Prymak M.V., Gomonnai A.V., Zahn D.R.T. Precipitates of selenium and tellurium in II-VI nanocrystal-doped glass probed by Raman scattering // Phys. Status Solidi B – 2011. – 248. – P. 674–679.