Strong room-temperature blue-violet photoluminescence of multiferroic BaMnF4

Abstract

BaMnF₄ microsheets have been prepared using a hydrothermal method. Strong room-temperature blue-violet photoluminescence has been observed (an absolute luminescence quantum yield of 67%) with two peaks located at 385 nm and 410 nm. More interestingly, photon self-absorption phenomenon has been observed, leading to an unusual abrupt decrease in the luminescence intensity at a wavelength of 400 nm. To understand the underlying mechanism of such emission, the electronic structure of BaMnF₄ has been studied using first principles calculations. The observed two peaks are attributed to electron transitions between the upper-Hubbard bands of the Mn's t_2g orbitals and the lower-Hubbard bands of the Mn's e_g orbitals. The Mott gap mediated d–d orbital transitions may provide additional degrees of freedom to tune the photon generation and absorption in ferroelectrics.