Spectroscopic characterization of Sm3+ in La3Ga5.5Ta0.5O14 single crystals

La3Ga5.5Ta0.5O14 single crystals with nominal Sm3+ concentrations of 0.5 at.% and 3 at.% were grown by the Czochralski method from iridium crucibles. Examination of chemical composition of manufactured crystals revealed that actual Sm3+ concentrations are 0.27 at.% and 1.96 at.%, respectively. Spectroscopic measurement encompassed acquisition of absorption spectra, luminescence spectra and luminescence decay curves at temperatures between 5 K and 300 K. Analysis of room temperature absorption spectra in the framework of the Judd-Ofelt treatment made it possible to determine radiative transition rates branching ratio values related to the 4G5/2 luminescence of Sm3+ ions. Crystal field splitting of Sm3+ multiplets involved in luminescence phenomena was inferred from absorption and emission spectra recorded at 5 K. It was found that absorption and luminescence transitions exhibit strong anisotropy and their intensities for σ-polarized spectra is higher by a factor of two roughly than those for π-polarized spectra. Observed strong inhomogeneous broadening of spectral bands was attributed to certain structural disorder of the host resulting from the substitution of octahedrally coordinated Ga3+ ions by Ta5+ ions. It follows from calculated and experimental values of luminescence branching ratio that about 80% of excitation energy of the 4G5/2 metastable level is converted to visible luminescence distributed into three bands peaking at 550 nm, 600 nm and 646 nm. It was concluded that the La3Ga5.5Ta0.5O14:Sm3+ system is promising for application as an orange-red emitting phosphor and deserves further investigation aimed at assessing its ability to show yellow laser emission.