When did the person that helped van Vleck develop CFT die?
Crystal field theory:  CFT was developed by physicists Hans Bethe and John Hasbrouck van Vleck in the 1930s. Hans Bethe: Hans Albrecht Bethe (] ; July 2, 1906 – March 6, 2005) was a German and American nuclear physicist who, in addition to making important contributions to astrophysics, quantum electrodynamics and solid-state physics, won the 1967 Nobel Prize in Physics for his work on the theory of stellar nucleosynthesis.
March 6, 2005