It depends on what particles are and the temperature of compacting. If the temperature was high enough the nanoparticles might suffer the recrystallization and grew.
I have made a pellet of only copper nanoparticles ( synthesized by electrolysis method without any capping / stabilizing agent). Is the pellet nano or bulk material at room temperature?
I have made the pellet (using pellet preparation technique for FTIR analysis) without KBr.