Synthesis and Optical Properties of Single Crystalline Phosphors Gd3In2Ga3O12:RE3+ (RE = Nd3+ and Ho3+) Grown via the Optical Float Zone Method

The continuous development of innovative optical materials with lanthanoid ions as activators has emerged as a modern sector of materials chemistry. Our experience with the fabrication of single crystals with the optical float zone has motivated us to investigate the luminescence of Nd3+ and Ho3+ ions in the garnets (Gd3-xREx)In2Ga3O12 (RE = Nd and Ho, x = 0; 0.15 and 0.30). Upon usage of an Ar/O2 (80:20 ratio) atmosphere and application of an auxiliary pressure (6 bar) to suppress In2O3 evaporation, single crystalline domain sizes in the order of ~ 6 x 6 x 1 mm³ obtained. Structural analysis confirmed the formation of a cubic garnet phase with space group Ia3 ̅d, with the substituents incorporated in accordance with Vegard’s law. Backscattered electron imaging and energy-dispersive X-ray spectroscopy were conducted, demonstrating a homogeneous elemental distribution within the crystals. Photoluminescence studies were carried out, revealing the characteristic narrow-line 4fn→4fn transitions of Nd3+ and Ho3+, with decay times in the sub-millisecond range, suggesting non-negligible cross-relaxation effects were present. Despite this, the large nearest-neighbour Gd–Gd distance (3.88 Å) in Gd3In2Ga3O12 and the low phonon cutoff energy (~700 cm 1) were found to limit cross-relaxation pathways, preserving significant photoluminescence brightness. These results highlighted the potential of Gd3In2Ga3O12:RE3+ single crystals as promising candidates for advanced optical applications.