Nanocomposites and nanomaterials 

Photoluminescence of Eu3+ ions in thin-film opals and resonator structures based on them with spatial localized feedback 
Moiseienko V.N., Gavrilyak V.R., Derhachov M.P., Ohiienko O.V. 
Physics, Electronics and Computer Systems Department, Oles Honchar Dnipro National University. Prospect Gagarina, 72, Dnipro-49010, Ukraine. 
E-mail: vnmois@ukr.net 

Resonatorless generation of light in an active scattering medium under the condition k L = 1 (k is wave vector of light, L is photon mean free path) is of both scientific and practical interest [1, 2]. 
The photoluminescence spectra of the C6H9EuO6xH2O salt in the pores of thin-film opals on a glass substrate, as well as in the pores of resonator structures based on them (see figure: 1 - D = 301 nm. 2 - D = 294 nm. 3 - salt-impregnated region) were measured. 
The excitation of the samples was carried out in the "reflection" geometry from the (111) plane by the radiation of semiconductor laser with λex= 405 nm. The spectra were measured using a DFS-12 double monochromator and a recording system in the photon counting mode with accumulation. 
In the measured spectra the radiative transitions in the energy spectrum of Eu3+ 5D0 → 7F0, 5D0 → 7F1, and 5D0 → 7F2 were observed at wavelength 580 nm, 592 nm and 617 nm respectively. The dependence of the intensities and splitting of the bands in the luminescence spectrum on the position of the stop-band and additional impregnation of the samples with glycerol has been established. An increase in the luminescence intensity (by a factor of 5) was observed for the bands located at the boundary of the stop band. The appearance of a narrow intense line in the photoluminescence spectra of the resonator structure in the region of 610 – 612 nm is revealed. It may be associated with the appearance of stimulated emission due to the formation of closed light trajectories during scattering of the exciting radiation in the globular structure of the film opal (random generation). 

1.	Antonio Consoli and Cefe Lopez. Emission regimes of random lasers with spatially localized feedback // Optics Express.-2016.-Vol.24, No.10, 10913. 
2.	Алимов О.К., Басиев Т.Т., Орловский Ю.В., Самойлович М.И. Преобразование люминесценции лазерных красителей в вынужденное излучение в опаловой матрице // Квантовая электроника.-2008.-38, №7.-С665-669.