  Electron spin flip in atoms or ions can cause neutrino pair emission, which
provides a method to explore still unknown important neutrino properties by
measuring spectrum of emitted photon in association, when electroweak rates are
amplified by a phase coherence among participating atoms. Two important
remaining neutrino issues to be determined are the absolute neutrino mass (or
the smallest neutrino mass in the three-flavor scheme) and the nature of
neutrino masses, either of Dirac type or of Majorana type. Use of Raman
scattered photon was recently proposed as a promising tool for this purpose. In
the present work we continue along this line to further identify promising ion
targets in crystals, calculate neutrino pair emission rates, and study how to
extract neutrino properties from Raman scattered photon angular distribution.
Divalent lanthanoid ions in crystals, in particular Sm$^{2+}$, are the most
promising, due to (1) its large number density, (2) sharp optical lines, (3) a
variety of available ionic levels. Rejection of amplified quantum
electrodynamic backgrounds is made possible to controllable levels by choosing
a range of Raman trigger direction, when Sm$^{2+}$ sites are at O$_h$ inversion
center of host crystals such as SrF$_2$.
