One may add that even in the case of use of a Cu tube and of a diffracted-beam monochromator the white raditiation from the tube will generate Cu fluorescence in you sample, which will contribute to you background as it goes "through" the monochromator. So Fe fluroscence may not be the only problem.
for the hint on the Cu fluorescence, which will be excited via the high energy part of the tube's bremsspectrum above Cu K-edge energy.
But I think, the Cu fluorescence background might be small because the x-ray K-shell attenuation cross-section rapidly goes down above the Cu K-edge energy (~8,9keV) for increasing photon energy (see the attached diagram). So only a small section of the bremsspectrum will significantly cause Cu fluoresecence background contribution.
Sanjeet Kumar Paswan , you should make a test scan with Cu tube. If the background is too large and you cannot handle this issue, then you have the alternative of option (b), using Co or Cr target, including option (a) monochromator/energy dispersive detection of Co or Cr K-alpha.
this effect was at least sufficiently strong to surprise me with the high background level when I measured Co powder with CoKalpha radiation on a machine with diffracted beam monochromator many years ago. Prior to this, I was not even aware of this effect. Of course, this effect does not occur upon use of a primary beam monochromator.