Judd-Ofelt analysis of β-NaGdF4: Yb3+, Tm3+ and β-NaGdF4:Er3+ single crystals

Hexagonal β-NaGdF4 single crystals were grown by the Bridgman technique, one doped with 5% Yb3+, 0.5% Tm3+ and the other with 1% Er3+. Based on polarized absorption spectra a Judd-Ofelt analysis was performed using the software RELIC. The energy barycenters of the room temperature absorption bands were used to refine the 4f wavefunctions in the intermediate coupling approximation, and obtain the Slater integrals F(2), (4), (6) and the spin-orbit coupling parameter ζ. The experimental oscillator strengths were fitted, using calculated matrix elements, to the three Judd-Ofelt parameters Ω2,4,6. The radiative lifetimes and branching ratios were determined and compared to experimental data. The oscillator strengths of selected transitions relevant to upconversion processes are discussed.