Interionic cross relaxation and tunable color luminescence in KY3F10:Tb3+ nano/microcrystals synthesized by hydrothermal approach

Luminescence and stability of Tb doped CaF2 nanoparticles

Luminescence properties of CaF₂:Tb³⁺ nanoparticles were studied in order to investigate the effect of CaF₂ native defects on the photoluminescence dynamics of Tb³⁺ ions. Incorporation of Tb ions into the CaF₂ host was confirmed by X-ray diffraction and X-ray photoelectron spectroscopy. Cross-relaxation energy transfer was observed from the photoluminescence spectra and decay curves upon excitation at 257 nm. However, the unusual long lifetime of the Tb³⁺ ion as well as the decreasing trend of emission lifetime of the ⁵D₃ level suggested the involvement of traps, which were further investigated by using temperature-dependent photoluminescence measurements, thermoluminescence and lifetime measurements at different wavelengths. This work highlights the critical role that the CaF₂ native defects play in the photoluminescence dynamics of Tb³⁺ ions incorporated in a CaF₂ matrix. The sample doped with 10 mol% of Tb³⁺ ions was found to be stable under prolonged 254 nm ultraviolet irradiation.

Color-tunable phosphor of Sr3YNa(PO4)3F:Tb3+via interionic cross-relaxation energy transfer

A series of color-tunable Sr₃YNa(PO₄)₃F:Tb³⁺ phosphors with a fluorapatite structure were synthesized by a traditional high-temperature solid state reaction. The emitting color tuning from blue to green can be observed by gradually increasing Tb³⁺ concentrations, which is attributed to the enhanced cross-relaxation (CR) between Tb³⁺ ions, as described by (⁵D₃, ⁷F₆)–(⁵D₄, ⁷F₀). The CR process is analyzed based on the Dexter and Inokuti–Hirayama model, which is assigned to the electric dipole–dipole interaction. The energy transfer critical distance between Tb³⁺ ions is evaluated to be 18.1 Å. In addition, the thermal quenching mechanism of Sr₃YNa(PO₄)₃F:Tb³⁺ is also investigated. At the general working temperature of an LED (423 K), the luminescence intensity still maintains 81% and 92% with the Tb³⁺ concentration of 10 and 30 mol%, respectively, indicating an excellent thermal quenching performance of Tb³⁺. Due to the good optical and thermal properties, the Sr₃YNa(PO₄)₃F:Tb³⁺ phosphor can be used as a promising green emitting phosphor candidate in the field of white light applications.

Color-tunable Sr₃YNa(PO₄)₃F:Tb³⁺ phosphors were obtained via cross-relaxation energy transfer, and exhibit superior thermal stability.