Y₂O₃–H₃BO₃:Eu³⁺ powders are synthesized using a mechanical alloying method, and their photoluminescence (PL) properties are investigated through luminescence spectrophotometry. For samples milled for 300 min, some Y₂O₃ peaks ([222], [440], and [622]) and amorphous formations are observed. The 300-min-milled mixture annealed at 800°C for 1 h with Eu = 8 mol% has the strongest PL intensity at every temperature increase of 100°C (increasing from 700 to 1200°C in 100°C increments). PL peaks of the powder mixture, as excited by a xenon discharge lamp (20 kW) at 240 nm, are detected at approximately 592 nm (orange light, ⁵D_o → ⁷F₁), 613 nm, 628 nm (red light, ⁵D_o → ⁷F₁), and 650 nm. The PL intensity of powder mixtures milled for 120 min is generally lower than that of powder mixtures milled for 300 min under the same conditions. PL peaks due to YBO3 and Y₂O₃ are observed for 300-min-milled Y₂O₃–H₃BO₃ with Eu = 8 mol% after annealing at 800°C for 1 h.