Resonance electronic Raman scattering in Erbium phosphate crystals

Resonance enhancement factors of 10 to 100 have been observed for the electronic Raman scattering transitions in crystals of pure ErPO₄ and 1% Er³⁺ diluted in LuPO₄. The resonances were excited by the 488.0-nm line of an argon-ion laser. This line is nearly coincident with the crystal-field levels of the ⁴F_7/2 multiplet of Er³⁺. The differences in relative intensities between the transitions in ErPO₄ and those in 1% Er³⁺ in LuPO₄ arise from shifts in the energy levels in the two systems and suggest that quantum-mechanical interference effects play an important role.