Novel deep-red photoluminescence with extraordinary high luminescence ratio of 5D0-7F4 at 702 nm to 5D0-7F2 at 620 nm in Sr2EuAlO5

A series of novel red-emitting Sr2EuAlO5 phosphors, both undoped and doped with rare earth elements Sm, Ce and Tb ions were synthesized using a solid-state method. The photoluminescent properties were investigated. For the Sr2EuAlO5 phosphor, the excitation spectra exhibited a broad charge transfer band ranging from 250 to 360 nm and some sharp peaks ranging from 450 to 550 nm, with the highest sharp peak at 463 nm. The emission spectra showed the red emission in both undoped and doped Sr2EuAlO5 phosphors, with the highest peak at 702 nm attributed to D-5(0)-> F-7(4) transition under different excitation wavelengths of 393 and 463 nm. Doping Tb ions into the host lattice Sr2EuAlO5 resulted in an extraordinary ultra-high luminescence ratio of (D0-7F4)-D-5 at 702 nm to (D0-7F2)-D-5 at 620 nm, which was approximately three times higher than that of Sr2EuAlO5. Ce-doped Sr2EuAlO5 phosphors altered the shape of excitation spectra and charge transfer phenomenon was observed, while Sm-doped Sr2EuAlO5 significantly enhancing the emission intensity at 702 nm. In this study site preferential occupancy based on bond energy calculations was reported for the first time to theoretically confirm the dopant ion sites. The results indicate that Sm and Tb ions preferentially occupy the Eu1 sites, while Ce ions only occupied the Sr2 positions. The CIE values (x = 0.6311, y = 0.3512) and high color purity of 94.8 % in Sr2EuAlO5: 10 % Sm ions indicate its suitability as a red phosphor for WLEDs.