Nanocomposites and nanomaterials

Photonic crystal effects in the luminescence spectra of europium compounds in the synthetic opal pores
Ohiienko O.V., Moiseyenko V.N., Shvets T.V.
Physics, Electronics and Computer Systems Department, Oles Honchar Dnipro National University. Prospect Gagarina, 72, Dnipro-49010, Ukraine. 
E-mail: kombi21251@outlook.com

We have previously studied the luminescent spectra of europium (III) acetate monohydrate in synthetic opal pores [1]. This work is devoted to the study of the effect of the spectral distribution of the density of optical states (DOS) of synthetic opal on the photoluminescence spectra of europium compounds (Eu2O3, C6H9EuO6×H2O) in opal pores. Europium (III) oxide with the formula Eu2O3 was preliminarily dissolved in aqua regia, followed by impregnation of synthetic opal samples in it. The salt C6H9EuO6ЧH2O (99.9%) (SIGMA-ALDRICH) was injected into the opal pores during the impregnation of the samples in an aqueous salt solution followed by drying at T=300K. The excitation of the opal samples was carried out in the "reflection" geometry from the (111) plane by the radiation of a semiconductor laser with λex=405nm. The luminescence spectra of the initial europium compounds and compounds in the opal pores demonstrate high intensity radiative transitions: 5D0→7F0, 5D0→7F1, 5D0→7F2. However, the spectral intensity distribution measured at T=300K for the spectra of europium compounds in the opal pores differed significantly from the spectra of europium compounds in the free state. The spectra of europium compounds in opal pores were continuous. The reason for this is that the measured luminescence spectrum of europium compounds in opal pores is completely determined by the spectral distribution of the transition frequencies in the europium ion and the spectrum of the density of optical states in the vicinity of these frequencies. After annealing the salt C6H9EuO6ЧH2O at T=1273K on an alundum substrate and in the opal pores, as a result of its dehydration and subsequent decomposition, europium oxide Eu2O3 was synthesized [1]. However, in this case, too, the luminescence spectrum of Eu2O3 in the opal pores differed significantly from the spectrum of europium oxide synthesized from a salt on a substrate. This is a convincing confirmation of the influence of photonic crystal effects on optic processes in europium ions. 

1.	Ohiienko Oleh V., Moiseyenko V.N., and Shvets T.V. Luminescent properties of europium (III) acetate monohydrate in synthetic opal pores // Molecular Crystals and Liquid Crystals.-2020.-701, №1.-P. 72–81.