Trivalent Dy<sup>3+</sup> and Eu<sup>3+</sup> Ions\nCodoped High-Entropy Gadolinium Yttrium Scandium Aluminum Garnet Crystals\nfor Promising Visible Solid-State Laser and Anticounterfeiting Applications

Rare earth ion-doped luminescent\nmaterials exhibit significant\npotential for application in visible solid-state laser and anticounterfeiting\napplications. The Czochralski method was employed to successfully\nsynthesize high-quality Dy<sup>3+</sup>, Eu<sup>3+</sup> codoped Gd<sub>3</sub>Sc<sub>2</sub>Al<sub>3</sub>O<sub>12</sub> (GSAG), and Gd<sub>2.79</sub>Y<sub>0.21</sub>Sc<sub>2</sub>Al<sub>3</sub>O<sub>12</sub> (GYSAG) single crystals. Comprehensive studies were conducted on\ntheir structural and physicochemical properties, luminescence properties,\nand fluorescence lifetime. The Dy,Eu:GSAG and Dy,Eu:GYSAG crystals\nboth display favorable thermal conductivity values of 5.56 and 5.43\nW m<sup>–1</sup> K<sup>–1</sup>, respectively, along\nwith commendable hardness properties of 7.241 and 7.247 kg/mm<sup>2</sup>. The emission color of the Dy,Eu:G(Y)SAG crystals can be\nadjusted from white light under a 355 nm excitation to orange-red\nlight under a 405 nm excitation and bright yellow light under a 450\nnm excitation. Additionally, the maximum stimulated emission cross-section\nfor both crystals was calculated under various wavelength laser excitations.\nThe fluorescence lifetime of the crystals at the <sup>4</sup>F<sub>9/2</sub> level (Dy<sup>3+</sup>) and the <sup>5</sup>D<sub>0</sub> level (Eu<sup>3+</sup>) was also examined. Notably, the fluorescence\nquantum efficiencies at the <sup>4</sup>F<sub>9/2</sub> level in Dy,Eu:GSAG\nand Dy,Eu:GYSAG were measured to be impressive at 91.3 and 92.7%,\nrespectively. The mechanism of resonance energy transfer between Dy<sup>3+</sup> and Eu<sup>3+</sup> was analyzed, indicating promising applications\nof Dy,Eu:G(Y)SAG in visible solid-state lasers and multimode anticounterfeiting.