Unravelling the effect of interstitial oxygen on the photoluminescence of Ce3+-doped Ca2BO3Cl and Ca3(BO3)2

Ce 3+ -doped Ca 2 BO 3 Cl and Ca 3 (BO 3 ) 2 are presented as promising phosphors for solid-state white light illumination, display, phototherapy, etc. Herein, we combined experimental and first-principles calculations to study the photoluminescence properties of Ce 3+ -doped Ca 2 BO 3 Cl and Ca 3 (BO 3 ) 2 under different preparation environment. The results show that the co-doped Na  +  ions have little effect on the luminescence of Ce 3+ ions doped Ca 2 BO 3 Cl and Ca 3 (BO 3 ) 2 . However, the luminous intensity of Ce 3+ /Na + ions co-doped Ca 2 BO 3 Cl greatly decreased with increasing oxidizing atmosphere. When sintering at 800 °C in air, the luminescence intensity was more than 10 times lower than that in a reducing atmosphere (5 % H 2  + 95 % N 2 ), whereas the luminescence intensity of Ce 3+ -doped Ca 3 (BO 3 ) 2 hardly changed. First-principles calculations revealed that, within an enhanced oxidizing atmosphere, the formation energy of interstitial oxygen (O i ) in Ca 2 BO 3 Cl:Ce 3+ ,Na + decreased from 2.84 to 0.31 eV, whereas in Ca 3 (BO 3 ) 2 :Ce 3+ , it decreased from 2.11 to 1.51 eV. The small formation energy (0.31 eV) of interstitial oxygen (O i ) in an oxidation atmosphere may lead to the formation of interstitial oxygen defects in Ca 2 BO 3 Cl:Ce 3+ ,Na + , which may result in the luminescence quenching of Ce 3+ ions in Ca 2 BO 3 Cl:Ce 3+ ,Na + ((Ce 3+ )∗+O 0 →Ce 4+ +O 1− ) and cause a decrease in the luminescence intensity. The study of the difference in resistance to oxidation between Ce 3+ -doped Ca 2 BO 3 Cl and Ca 3 (BO 3 ) 2 is highly important for further improving current luminescent materials and developing new functional materials.