Doping Y₂O₃ with Mn⁴⁺ for energy-efficient lighting

Developing energy-efficient LEDs that emit warm white light requires new red phosphors with appropriate emission wavelengths and band widths. Mn⁴⁺-activated Y₂O₃ is a potential red LED phosphor with narrow emission and improved emission wavelength compared to previously known Mn⁴⁺-activated oxide phosphors. In this work, the dopability and the oxidation state of Mn in Y₂O₃ are investigated based on the formation energies of native defects, Mn dopants, and divalent co-dopants (i.e., Ca, Sr, Cd, and Zn) calculated using hybrid density functional theory. We found that Mn⁴⁺ is difficult to form in Y₂O₃ without co-doping. Stabilizing Mn⁴⁺ on Y³⁺ sites (forming Mn+Y donors) requires the co-doping of compensating acceptors (Ca or Sr) in oxygen-rich growth environments.