Ab Initio-Aided Sensitizer Design for Mn⁴⁺-Activated Mg₂TiO₄ as an Ultrabright Fluoride-Free Red-Emitting Phosphor

Abstract

Red-light phosphor materials are crucial components in solid-state lighting (SSL) for simulating natural sunlight. Mn-doped Mg 2 TiO 4 is a promising fluoride-free redemitting phosphor; however, a sensitizer is necessary to enhance its brightness. In this work, we perform ab initio calculations based on the density functional theory (DFT) to systematically examine the electronic-band coupling between the luminescent center, Mn, and several possible sensitizers, Zn, Nb, Mo, In, Sn, and Ta. Nb was identified as the optimal sensitizer. Well-crystallized 0.1 at. % Mn and 0.0−0.7 at. % Nbcodoped Mg 2 TiO 4 were synthesized at 1450 °C. Synchrotronradiation-based X-ray absorption spectroscopy (XAS) experimentally validated the proposed atomistic structure, indicating that the Nb 5+ dopant substitutes Ti 4+ at the 16d sites, leading to the formation of Ti vacancies and of a parasitic MgTiO 3 phase. Effective sensitization, resulting in a 243% enhancement of the photoluminescence intensity, was achieved. The 0.1 at. % Mn and 0.5 at. % Nb-codoped Mg 2 TiO 4 were obtained as an ultrabright "rare-earth-free" (RE-free) and "fluoride-free" red-light phosphor.

Tuning the Mn4+Coordination Environment in Mg2TiO4through a Codoping Strategy for Enhancing Luminescence Performance

“…To improve the luminescence efficiency, it is of vital importance to effectively control the chemical composition, phase structure, and site selective substitution of doped materials to improve the matrix microstructure of the luminescent center. − In this case, the design of an ion doping system can improve luminescence performance by modulating the coordination environment of Mn 4+ ions. , Because three electrons of Mn 4+ 3d are in the outer shell, the emission peak position and emission intensity of Mn 4+ are sensitive to the coordination environment. The emission peak of the Mn 4+ -activated phosphor family can be controlled in the range of 660 to 780 nm through manipulation of the nephelauxetic effect, crystal-field splitting, the Stokes shift, and other factors .…”

Cation Substitution Induced Adjustment on Lattice Structure and Photoluminescence Properties of Mg14Ge5O24:Mn4+: Optimized Emission for w‐LED and Thermometry Applications

“…Mn 4+ ‐activated narrow‐emitting red phosphors have aroused great concern in recent years due to their meaningful application in optoelectronic devices, no matter for decreasing the correlated color temperature (CCT) in the field of lighting source or using in wide‐gamut backlighting devices . Given the exposed outer electron in 3d 3 electronic configuration of Mn 4+ ions, its optical property is sensitive to the coordination environment of host matrix .…”

“…Moreover, the use of toxic hydrofluoric acid during the preparation easily damages the environment and the health of people . Therefore, seeking some efficient methods to enhance the stability of fluoride phosphor particles or to explore other alternative phosphor hosts is necessary for developing efficient Mn 4+ ‐doped red phosphors . Among a variety of alternative host matrices, oxides are considered as the ideal matrices for Mn 4+ doping.…”

Defect modulation and luminescence improvement of Mn4+-activated La(Mg, Nb)O3 phosphor with improved stability for plant cultivation

“…The PL spectra ranged from 670-720 nm with a full width at half maximum (FWHM) of 35 nm, which originated from the characteristic transition 2 E g -4 A 2g of Mn 4+ . 8,16,31 Correspondingly, the emission intensity greatly improved 4.15 times by decreasing the molar ratio of Mg/Nb and came to a maximum at x = 0.24. As the Nb 5+ concentration increases, more free electrons can be introduced and further affect the oxygen valence.…”