Abnormal narrow spectral lines in Y₂SiO₅:Pr³⁺ and

YVO₄:Eu³⁺ nanocrystals at room temperature

The homogeneous linewidth of impurity centres optical transitions is closely concerned with so-called time of phase relaxation T₂. Dephasing time T₂ plays an important part in the wide set of impurity ions optical resonances applications such as optical memory cells and quantum computers. For impurity RE ions at low temperatures the value of dephasing time can vary in the range of 100 ns – 0.1 ms. Practical application of optical resonances requires the impurity crystals with large T₂. Thus there is the strong request for materials providing minimal inhomogeneous broadening of optical transitions and (that is the most important) the minimal contribution to the homogeneous width determined by the phonon-stimulated processes. At the same time for the real operation with optical resonances in the case of doped bulk crystals the deep cooling for phonon impurity centre scattering suppression is required.
The contribution of the phonon scattering processes to the homogeneous linewidth strongly depends on the phonon state density. Depletion of phonon state density observed for nanocrystals leads to suppression of the fast nonradiative relaxation of impurity centre electron states. Increasing of nanocrystal size must lead unambiguously to the phonon density increasing manifesting itself in the increasing of phonon contribution to the impurity ion homogeneous linewidth. The experimental results totally confirm our predictions.

Our results:
We have observed that the luminescence spectrum of Y₂SiO₅:Pr³⁺ nanocrystal at room temperature looks like the spectrum of Y₂SiO₅:Pr³⁺ bulk crystal under the deep cooling.
At the same time the spectral lines of Y₂SiO₅:Pr³⁺ bulk crystal at room temperature are sufficiently broader. The average linewidth of Y₂SiO₅:Pr³⁺ bulk crystal spectral lines at room temperature is about 100 cm^_-1, whereas for the same nanocrystals it is about 20 cm^-1.

For the confirmation of observed spectral peculiarities generality YVO₄:Eu³⁺ nanocrystal has been investigated. Spectral lines of Eu³⁺ ion luminescence spectrum in YVO₄:Eu³⁺ nanocrystals remain narrow at the room temperature making the spectrum well structured .

Main publications:

• Yu.V. Malyukin, A.A. Masalov. Control of electron–phonon dynamics by quantum confinement in isolated Y₂SiO₅:Pr³⁺ nanocrystal// Optical Materials – 2009. – v.31., № 9. – P.1849–1852. abstract

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