Jahn-Teller effect in Ag2+ doped KCl and NaCl: Is there any influence of the host lattice?

A puzzling situation is explained through ab intio calculations on KCl:Ag2+ and NaCl:Ag2+. In fact while spin Hamiltonian parameters for both systems are nearly identical the transition temperature for passing from a static to an isotropic spectrum is 160 K for KCl:Ag2+ but only equal to 95 K for NaCl:Ag2+.