KRE(CO3)2 (RE = Eu, Gd, Tb): new mixed metal carbonates with strong photoluminescence and large birefringence

Three new potassium rare earth carbonates, namely KRE(CO3)2 (RE = Eu, Gd, Tb), were synthesized successfully. Their structures feature a novel [RE(CO3)2]− 3D framework with 1D channels along the c axis filled with K+ cations. Among them, KEu(CO3)2 and KTb(CO3)2 emit strong red and green photoluminescence, respectively. The birefringence values of KRE(CO3)2 were measured as 0.149, 0.162 and 0.215 at 546 nm, respectively. Remarkably, KTb(CO3)2 has the largest experimental birefringence among carbonates reported.