(Ba_1-xHo_x)(Ti_1-xEr_x)O₃ ceramics (abbreviated BHTE) were prepared using the mixed-oxides route. The crystal structure, solid solubility, and defect chemistry of BHTE were investigated using X-ray diffraction (XRD), electron paramagnetic resonance (EPR) and photoluminescence. The results indicated that the solubility limit of Ho³⁺/Er³⁺ ions in the BaTiO₃ lattice is x = 0.01 and BHTE ceramics has a tetragonal perovskite structure. When x is more than 0.02, a small amount of Er₂O₃ separates out in BHTE, accompanied by Ba₆Ho₂Ti₄O₁₇ phase. The site occupation, solid solution formation, and defect chemistry are discussed.