The dynamics of the photoluminescence of Pr³⁺ in mixed lanthanum yttrium oxyorthosilicate hosts

Praseodymium (Pr³⁺) doped mixed lanthanum yttrium oxyorthosilicate (LaYSiO₅) powder phosphors were synthesized using urea-assisted combustion method. The molar ratio of La:Y were varied in the following manner: La_2-xY_xSiO₅ (x = 0, 0.5, 1, 1.5, 2), were x = 0 is pure La₂SiO₅, x = 2 is pure Y₂SiO₅ and x = 0.5, 1, and 1.5 are the admixtures of the two compounds. The X-ray diffractometer results showed that the La₂SiO₅ and Y₂SiO₅ crystalized in their pure monoclinic phases, while their admixtures are both present in the same phase. The Burstein–Moss (BM) shift was used to explain the increase observed in the band gap after doping. The influence of the host crystal field on the branching ratios of the photoluminescence emission intensities of the ³P₀ and ¹D₂ energy levels of Pr³⁺ were studied. The electronic transition from the ³P₀ transition dominated the emission spectra when x = 0, while the ¹D₂ electronic transition dominated when x = 2. The variation in the branching ratios of the ³P₀ and ¹D₂ emission with the change in the molar ratio of La:Y could be due to ³P₀ → ¹D₂ non-radiative transitions, which increased with the crystal field of the host as the value of x increased (i.e., as the molar ratio of Y increases). Furthermore, it was shown that the ³P₀ emission lines emerged from Pr³⁺ ions occupying La1 and Y1 sites of La₂SiO₅ and Y₂SiO₅ respectively, while the ¹D₂ emission lines emerged from Pr³⁺ ions occupying La2 and Y2 sites. The decay curve showed three lifetime components from both ³P₀ and ¹D₂ emission lines, with the ¹D₂ lines having higher lifetimes in all cases.