  We theoretically investigate the fluorescence intensity correlation (FIC) of
Ar clusters and Mo-doped iron oxide nanoparticles subjected to intense,
femtosecond and sub-femtosecond XFEL pulses for high-resolution and elemental
contrast imaging. We present the FIC of {\Ka} and {\Kah} emission in Ar
clusters and discuss the impact of sample damage on retrieving high-resolution
structural information and compare the obtained structural information with
those from the coherent difractive imaging (CDI) approach. We found that, while
sub-femtosecond pulses will substantially benefit the CDI approach,
few-femtosecond pulses may be sufficient for achieving high-resolution
information with FIC. Furthermore, we show that the fluorescence intensity
correlation computed from the fluorescence of Mo atoms in Mo-doped iron oxide
nanoparticles can be used to image dopant distributions.
