However, a modern theoretical treatment by Modinos assumes that the band-structure of the emitting material must also be taken into account. This would introduce a second correction factor "λ"B into "λ"R, giving formula_6. Experimental values for the "generalized" coefficient "A"G are generally of the order of magnitude of "A"0, but do differ significantly as between different emitting materials, and can differ as between different crystallographic faces of the same material. At least qualitatively, these experimental differences can be explained as due to differences in the value of "λ"R.