Abstract: Stark levels and EPR parameters of Er³⁺ doped in Bi₄Ge₃O₁₂ crystal were studied by diagonalizing 364×364 complete energy matrices. Simultaneously, the crystal-field and J-J mixing effects on the EPR g-factors from the higher lying manifolds were evaluated, quantitatively. The results indicate that the dominant J-J mixing contribution from manifold ²K_15/2 accounts for about 2.5% for the Er³⁺. However, the most significant high-order mixing effect is from the crystal-field admixture between the first excited manifold ⁴I_13/2 and ground manifold ⁴I_15/2, where the contribution to g_⊥ is almost twice as much as that to g_// (0.21% for g_⊥, 0.092% for g_//).The other crystal-field and J-J mixing effects from the higher lying manifolds can be neglected. Therefore, only considering the contribution of ground manifold ⁴I_15/2 to EPR g-factor is a good approximation for the complex system doped with Er³⁺ ions.

Key words: Er³⁺, Bi₄Ce₃O₁₂, crystal-field effect, J-J mixing effect, EPR g-factor