Sensitization of luminescence from Sm3+ ions in fluoride hosts K2YF5 and K2GdF5 by doping with Tb3+ions

Spectroscopic properties and energy transfer mechanisms for isostructural fluoride K₂YF₅ and K₂GdF₅ crystals singly and doubly doped with different concentrations of Tb³⁺ and Sm³⁺ ions have been investigated under excitation in the deep ultraviolet (DUV) and vacuum UV (VUV) spectral regions. In these hosts luminescence of Sm³⁺ ions is enhanced under DUV excitation by doping with Tb³⁺ ions, namely, the Sm³⁺ excitation spectra show additional intense excitation in the region of Tb³⁺ spin-allowed 4f – 5d transitions at 200–220 nm due to energy transfer from Tb³⁺ to Sm³⁺. The decay curves of Tb³⁺ ion luminescence have been measured at room temperature for the series of samples containing different concentration of Sm³⁺ and have been fitted by the Inokuti-Hirayama model. The results have revealed that the dipole-dipole interaction is the dominant interaction mechanism in the energy transfer process from Tb³⁺ to Sm³⁺ ions. The probability (W_ET) and the efficiency (E_ET) of energy transfer from Tb³⁺ to Sm³⁺ increase depending on the Sm³⁺ concentration in these crystals.