Understanding the role of particle size on photophysical properties of CdS:Eu3+ nanocrystals

Here, we report the role of particle size on the photoluminescence (PL) properties of CdS:Eu3+ nanocrystals by steady-state and time-resolved PL spectroscopy. It is found that the average decay time 〈τ〉 of undoped CdS nanocrystals increases with increasing the size. The fast component (nanosecond) is assigned due to trapping and slow component (above 10 ns) is due to defect-related emission. The decrease of fast component from 6.6 to 1.32 ns and the slow component from 20 to 14.6 ns of CdS (host) is observed in presence of Eu ions, indicating that the energy transfer occurs from CdS nanoparticles to Eu3+ ions. The decay time of Eu3+ in CdS shows two decay components (microsecond scale) and we believe that the fast component is attributed to surface-bound Eu3+ ions and slow component is due to lattice-bound Eu3+ ions. Analysis suggests that PL efficiency of Eu3+ ions depends on size of nanoparticles.