Y 2 O 3 –H 3 BO 3 :Eu 3+ powders were synthesized by the mechanical alloying (MA) method, and their structural and photoluminescent characteristics were investigated by X-ray diffractometry (XRD), scanning electron microscopy (SEM), thermogravimetric/differential thermal analysis (TG/DTA), and luminescence spectrophotometer. The crystallite size of the powder mixture milling for 30 minutes (min) by the Willaimson–Hall method was approximately 58.8 nm with strain of 0.00141; overall, the internal strain increased with the milling time (t m ). The morphology of the powder mixture with t m , as observed by SEM, divided into three different stages: agglomeration (0 < t m ≤ 30 min), disintegration (30min < t m ≤ 120 min), and homogenization (120min < t m ≤ 300 min). The transition temperature and the weight reduction rate of the sample powders were 645.58 °C and 2.851%, respectively. Furthermore, the photoluminescence of the powder mixture excited to 240 nm by a zenon discharge lamp (20 kW) was detected near 592 nm( 5 D o → 7 F 1 ), 613 nm, 628 ( 5 D o → 7 F 2 ), and 650 nm ( 5 D o → 7 F 3 ).