Glass-ceramics containing rare earth gallium garnets were obtained using glass compositions as reactional medium. This work reports on the synthesis, and structural, morphological, and optical characterizations of Er3+ and Tm3+-doped Yb3Ga5O12 crystals prepared from controlled cooling of heavy metal oxide glass melts. Micrometric cubic crystals were obtained by controlling the cooling of a rare earth-supersaturated glassy composition melted at high temperature. Crystals with sizes ranging between 5 and 150 mu m were formed into the glass matrix. A gallium garnet phase corresponding to space group Ia-3d was identified by X-ray diffraction and confirmed by Rietveld simulations. The morphology of crystals was studied by optical and scanning electron microscopies, while chemical elements were mapped by electron dispersive X-Ray spectroscopy. The glass phase was studied by XRD, thermal analysis and Raman spectroscopy. The optical properties of both glass and glass-ceramic materials were evaluated by UV-Vis and luminescence spectroscopies. Micro-luminescence measurements confirmed that rare earths were incorporated into the crystalline phase. Intense upconversion emissions of Er3+ (550 and 660 nm) and Tm3+ (800 nm) were observed when the glass-ceramics were pumped at 980 nm. These new glass-ceramics are excellent candidates for the development of photonic devices. (C) 2021 Elsevier B.V. All rights reserved.