Abstract Tm 3+ /Yb 3+ doped glass ceramics, containing single phase of YAG micro-crystals with several preferred orientations and a dominant one (4 4 4) in the matrix, which present the primary particle size of ∼46 nm and the secondary particle size of ∼8 μm, have been prepared by heat-treating the Li 2 O–Y 2 O 3 –Al 2 O 3 –SiO 2 (LYAS) precursor glasses. Judd-Ofelt parameters Ω t ( t = 2, 4, 6) are derived to be 5.14 × 10 −20 , 1.11 × 10 −20 , and 1.19 × 10 −20 cm 2 , respectively, indicating high inversion asymmetry and strong covalent environment in the precursor glasses. Efficient near-infrared (NIR), weak red, intense blue and rare UV multi-photon upconversion emissions of Tm 3+ are captured in Tm 3+ /Yb 3+ doped LYAS glasses and YAG glass ceramics. Obvious Stark splitting in the glass ceramics manifests that rare earth ions have been incorporated into YAG lattices. The comparison of spectral behaviors of the glass and glass ceramic samples will be helpful for further exploring the novel phosphors applied to illumination and display.