Linter cellulose fiber based nanocomposites were prepared by functionalizing the fibers with [Fe(hptrz)(3)](OTs)(2) spin-crossover nanoparticles and acridine orange dye molecules. The composites were characterized by electronic (UV-vis and fluorescence) and vibrational (Raman, FTIR) spectroscopies as well as by electronic and optical microscopies. The cellulose sheets prepared from the nanocomposite show significant thermochromic and thermofluorescent effects associated with the spin transition phenomenon, providing scope for paper thermometry and anti-counterfeit applications.