Rare-earth scheelites represent a diverse family of compounds with multiple degrees of freedom, which enables the incorporation of a wide range of lanthanide color centers. Precise positioning of quantum objects is attainable by the choice of alkali cations and lattice connectivity of polyanion units. Herein, we report the structure-dependent energy transfer and lattice coupling of optical transitions in La- and Dy-containing scheelite-type double and quadruple molybdates NaLaDy(MoO) and NaLaDy(MoO). X-ray excitation of La core states generates excited-state electron-hole pairs, which, upon thermalizing across interconnected REO polyhedra in double molybdates, activate a phonon-coupled excited state of Dy. A pronounced luminescence band is observed corresponding to optical cooling of the lattice upon preferential radiative relaxation from a "hot" state. In contrast, combined X-ray absorption near-edge structure and X-ray-excited optical luminescence studies reveal that such a lattice coupling mechanism is inaccessible in quadruple molybdates with a greater separation of La-Dy centers.
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