Constructing a Model for Tuning the Thermal Quenching Properties of Bismuth-Doped Phosphors by Energy-Gap Modulation

Thermal quenching performance is a huge challenge in the application of phosphor materials. In this paper, the relationship between the energy gap of luminescent ions and the thermal quenching activation energy (ΔE) is discussed from the angle of energy-level splitting for the first time. When the proportion of coordination cations (Nb–Ta) in the matrix is adjusted, the dissimilarity in bond lengths and bond angles of the two crystal configurations (NbO6/TaO6) makes the crystal electron cloud expand, the decrease in atomic orbital overlap reduces the covalency, and the nephelauxetic effect enlarges the bond length between the dopant and the ligand, thus decreasing the crystal field splitting energy of trivalent bismuth ions, which weakens the splitting degree of the P energy level, leading to an increase in the energy gap from 3.854 to 4.101 eV. Interestingly, the thermal quenching performance of YNb1–xTaxO4:Bi3+ (YNTO:Bi3+) also changes with the Nb–Ta ratio, and the thermal quenching activation energy is positively correlated with the energy-gap value. Guided by the density functional theory calculations on the ligand structure, we establish the functional relationship between the energy-gap value and ΔE; the tuning of the thermal quenching activation energy of the Bi-doped phosphors from 0.473 to 0.543 eV is realized by controlling the ratio of Nb5+/Ta5+. The Bi3+–Eu3+ double-doped white-light-emitting phosphors prepared according to this mechanism can still emit warm white light at 463 K. The topological chemical design of the ligand configuration realizes the modulation of the thermal quenching activation energy, and this method can be used as a model to design various novel ΔE-adjustable fluorescent powder materials.