  We report on low temperature photoluminescence (PL) and EPR study of bulk
polycrystalline ZnO . Variation of peak position of donor bound exciton
transition (D1XA) and FXAn=1-1LO with pump intensity show red shift and blue
shift respectively due to exciton-exciton scattering. EPR spectra reveals three
peaks at g value of 1.985, 1.956 and 1.939 respectively, g=1.956 and g=1.985 is
due to shallow donors Zn interstitial and oxygen vacancy respectively An EPR
spectrum at 100 K reveals higher degree of asymmetry and hyperfine splitting
due to crystal field and inhomogeneous relaxation of paramagnetic centers.
Strength of crystal field splitting (CFS) and spin orbit coupling (SOC) in
sample is discussed using PL peak position of various excitonic emissions.
Whereas, inhomogeneous relaxation of paramagnetic centers is discussed in terms
of their activation energy during thermal quenching process.
