The influence of post-preparation annealing atmospheres on the optical properties and energy transfer between Pr 3+ and Dy 3+ in mixed lanthanum-yttrium oxyorthosilicate hosts

Abstract The effect of post-annealing atmospheres (air and Ar-H 2 ) on the optical properties of La 2- x Y x SiO 5 ( x  = 0, 0.5, 1, 1.5 and 2) co-doped 0.25 Pr 3+ and 0.25 Dy 3+ powder phosphors were studied. The X-ray diffraction patterns showed that the as-prepared samples have higher full width at half maximum (FWHM) than the annealed samples. The elemental composition, oxidation states, and chemical and electronic states of the phosphors were determined using the X-ray photoelectron spectroscopy. The band gap values determined from the diffuse reflectance spectra were shown to increase following the post-annealing treatments (with the values increasing in the following manner: Ar-H 2 -annealed > air-annealed > as-prepared). The photoluminescence intensities of the phosphors also followed the same trend as the band gap values. Two different cases of the photoluminescence mechanisms were proposed for the La 2- x Y x SiO 5 : 0.25 Pr 3+ , 0.25 Dy 3+ phosphors. Case 1: The 4f5d energy level of Pr 3+ lies within the band gap of the host and energy transfer was observed from Pr 3+ to Dy 3+ via the overlapping 4f5d emission peak of Pr 3+ and the 4 I 15/2 excitation peak of Dy 3+ . Case II: The 4f5d energy level of Pr 3+ lies close or inside the conduction band of the host and the energy transfer was not observed from Pr 3+ to Dy 3+ . The CIE colour coordinates of the phosphors showed tunable emission colours (blue, red and white).