Temperature dependent energy transfer to Eu³⁺ emission centres in K₅Eu(MoO₄)₄ crystals

Luminescence properties of a palmierite-type K₅Eu(MoO₄)₄ crystal were studied in a wide temperature range of 7-650 K. Eu³⁺ ions are shown to occupy at least three non-equivalent positions in the palmierite-type structure, forming emission centres with slightly different characteristics due to an incommensurate modulated disordering. The relative intensity of the Eu³⁺ emission bands originating from the ⁵D₀ and ⁵D₁ terms is shown to depend on excitation energy and the origin of the observed differences is discussed. It is shown that quenching temperature of the Eu³⁺ emission depends on excitation energy that is explained by energetical overlap of the 4f-4f Eu³⁺ transitions with the Urbach tail of the fundamental absorption region. Energy transfer processes to the Eu³⁺ emission centres were studied using the methods of time resolved spectroscopy.