5d-4f Emission of Nd$^{3+}$, Sm$^{3+}$, Ho$^{3+}$, Er$^{3+}$, Tm$^{3+}$ Ions in Alkaline Earth Fluorides

Emission and excitation spectra of CaF ₂ , SrF ₂ , BaF ₂ doped with Nd ³⁺ , Sm ³⁺ , Ho ³⁺ , Er ³⁺ , Tm ³⁺ excited by vacuum ultraviolet photons or by x-rays were studied. Decay times of the Nd ³⁺ emission near 180 nm at 7 K were 17.7, 15.3, 12.3 ns in CaF ₂ , SrF ₂ , BaF ₂ respectively. 4f n -1 5d ¹ -4f n luminescence bands were found at 170-200 nm for Sm ³⁺ ions and at 140-190 nm for Ho ³⁺ . No excitation of 5d-4f emission of Nd ³⁺ and Tm ³⁺ was observed in the region of band-to-band transitions below 127 nm (BaF ₂ ), 120 nm (SrF ₂ ) and 115 nm (CaF ₂ ). Emission spectra of Nd and Er doped alkaline-earth fluoride crystals under x-ray excitation were studied with concentration of impurity from 0.01 to 10 molar %. For the Nd ³⁺ and Er ³⁺ 5d-4f emissions in SrF ₂ the light yields were estimated as 30-40 ph/Mev.