A novel red Ca8.5Pb0.5Eu(PO4)7 phosphor for light emitting diodes application

Ca 9– x Pb x Eu(PO 4 ) 7 (0 ≤ x ≤ 1) solid solutions with a whitlockite-type (or β -Ca 3 (PO 4 ) 2 -type) structure (sp.gr. R 3 c ) were prepared by a standard solid-state method in air. Their luminescent properties under near-ultraviolet (n-UV) light were investigated. Excitation spectra of Ca 9– x Pb x Eu(PO 4 ) 7 showed the strongest absorption at about 395 nm, which matches well with commercially available n-UV-emitting GaN-based LED chips. Emission spectra indicated an intense red emission due to the 5 D 0 → 7 F 2 transition of Eu 3+ , with a maximum in the intensity for Ca 8.5 Pb 0.5 Eu(PO 4 ) 7 . The emission intensity of Ca 8.5 Pb 0.5 Eu(PO 4 ) 7 was about 1.8 times higher than that of a Ca 9 Eu(PO 4 ) 7 phosphor. We suggest that the introduction of Pb 2+ is an efficient approach to enhance luminescence properties of such phosphors. We clarified the influence of the Ca 2+ → Pb 2+ substitution on intensities of three bands for the 5 D 0 → 7 F 0 transition in excitation spectra of Ca 9– x Pb x Eu(PO 4 ) 7 . In addition, we found a reversible first-order phase transition from R 3 ≿ to R 3 ¯ ≿ symmetry by second-harmonic generation in the range from 753 K ( x = 1) to 846 K ( x = 0).