Color-Tunable Luminescence and Energy Transfer Properties of Ca₉Mg(PO₄)₆F₂:Eu²⁺, Mn²⁺ Phosphors for UV-LEDs

Eu 2+ -, Mn 2+ -activated Ca 9 Mg(PO 4 ) 6 F 2 (CMPF) phosphors with blue to yellow color-tunable emission properties have been synthesized via high-temperature solid-state reaction method. The crystal structure of Ca 9 Mg(PO 4 ) 6 F 2 has been identified by Rietveld refinement. The different crystallographic sites of Eu 2+ in CMPF:Eu 2+ phosphors have been confirmed by virtue of their fluorescence decay lifetimes. The Eu 2+ -activated CMPF phosphors exhibit broad excitation spectra from 200 to 420 nm (which matches well with the UV-based LED chips) and emission spectra from 380 to 580 nm centered at 454 nm. Energy transfer from Eu 2+ to Mn 2+ ions in Eu 2+, Mn 2+ codoped CMPF samples is possible because of the spectral overlap between Eu 2+ emission and Mn 2+ excitation spectra, and the constant fall of fluorescence decay lifetimes of Eu 2+ ion with increasing Mn 2+ concentration demonstrates the occurrence of it, which provides the color-tunable emission from blue to yellow through adjusting Mn 2+ concentration. The energy transfer mechanism between Eu 2+ and Mn 2+ ions is verified to be electric dipole–quadrupole interaction by analyzing the experimental results. The critical distance between them calculated by concentration quenching (14.57 Å) and spectral overlap methods (14.90 Å) are consistent, which testifies the energy transfer mechanism above from Eu 2+ to Mn 2+ is appropriate. These results show CMPF:Eu 2+, Mn 2+ phosphors could be anticipated for UV-pumped white-light-emitting diodes (wLEDs).