CaY_1−xAl_1+xO₄:2%Eu (x = 0, 0.1, 0.2) phosphors have been synthesized via a solid-state reaction process. XRD patterns indicate that they are pure phase. The photoluminescence properties of the CaY_1−xAl_1+xO₄:2%Eu phosphors exhibit both the blue emission of Eu²⁺ (4f⁶5d¹–4f⁷) and red-orange emission of Eu³⁺ (⁵D₀–⁷F_1,2,3,4) under UV light excitation, which showed that the Eu^3+/2+ co-doping system was obtained by adjusting the Al/Y ratio. Eu³⁺ ions can be reduced to Eu²⁺ ions when the Al/Y ratio was changed. In this work, the bond energy method was used to determine and explain the mechanism of the site occupation of Eu ions entering the host matrix. Also, the emission spectrum showed an unusual comparable intensity ⁵D₀–⁷F₄ transition peak. The relative intensity of ⁵D₀–⁷F₂ and ⁵D₀–⁷F₄ can be stabilized by changing the relative proportions of Al³⁺ and Y³⁺. Furthermore, this was explained by the J–O theory.