  We report on low temperature photoluminescence study of ZnO. The
photoluminescence profile at 6K reveals FXA n=1, FXn=2A and FXn=1B peaks at
367.04 nm, 363.17 nm and 365.66 nm respectively together with neutral donor
bound exciton D0 1XA at 370.48 nm. The first, second, and third order
longitudinal optical phonon replica of free exciton transitions FXn=1A at
375.03, 383.10, and 391.54 nm respectively, and donor acceptor pair transition
at 386.73 nm is observed. The dynamics of D0 1XA and 1LO with excitation
intensity is presented. A red shift of photoluminescence peak position of D0
1XA and blue shift of 1LO with increase of pump intensity is observed. The peak
photoluminescence intensity of D0 1XA increases superlinearly with increase of
pump intensity.
