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

Abstract

Ce³⁺-doped Ca₂BO₃Cl and Ca₃(BO₃)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 Ce³⁺-doped Ca₂BO₃Cl and Ca₃(BO₃)₂ under different preparation environment. The results show that the co-doped Na ⁺ ions have little effect on the luminescence of Ce³⁺ ions doped Ca₂BO₃Cl and Ca₃(BO₃)₂. However, the luminous intensity of Ce³⁺/Na⁺ ions co-doped Ca₂BO₃Cl 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 % H₂ + 95 % N₂), whereas the luminescence intensity of Ce³⁺-doped Ca₃(BO₃)₂ hardly changed. First-principles calculations revealed that, within an enhanced oxidizing atmosphere, the formation energy of interstitial oxygen (O_i) in Ca₂BO₃Cl:Ce³⁺,Na⁺ decreased from 2.84 to 0.31 eV, whereas in Ca₃(BO₃)₂:Ce³⁺, 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 Ca₂BO₃Cl:Ce³⁺,Na⁺, which may result in the luminescence quenching of Ce³⁺ ions in Ca₂BO₃Cl:Ce³⁺,Na⁺ ((Ce³⁺)∗+O⁰→Ce⁴⁺+O¹⁻) and cause a decrease in the luminescence intensity. The study of the difference in resistance to oxidation between Ce³⁺-doped Ca₂BO₃Cl and Ca₃(BO₃)₂ is highly important for further improving current luminescent materials and developing new functional materials.