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.