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Zinc oxide (ZnO) nanoparticles (NPs) were prepared in distilled deionized water by pulsed laser ablation for various ablation durations (5, 10 and 15 mins) and pulse energies (30, 45, 60 mJ/pulse). All the samples possessed characteristic Raman peaks; E2 (low), E2 (high), A1 (TO), A1 (LO) etc. attributed to the wurtzite crystal structure of ZnO [1]. TEM and SAED results revealed nearly spherical nanocrystals depicting crystalline wurtzite ZnO phase with average size reducing from ~15 nm at low fluence to ~ 27 nm at high fluence, while distributions narrowing from 14 nm to 9 nm consistent with enhanced crystalline ordering. The size and shape of the nanoparticles were affected only slightly by the ablation time but more by laser energy. The size variation with time was explained with competition between crystalline growth and fragmentation [2]. UV–Vis absorption showed size-dependent shifts, while steady-state photoluminescence (PL) exhibited a clear transition from broad to sharp near-band-edge (NBE) ultraviolet emission, along with increasing less dominant defect level emissions (DLE) in visible spectral region, with increasing fluence. In addition to this, a, hardly effected by experimental conditions, were also observed [3]. Notably, time-resolved PL (TRPL) measurements yielded stable exciton lifetimes of ~185–194 ps across all conditions, confirming radiative recombination dominance independent of size and defect variations. The results demonstrate that laser fluence provides effective control over ZnO NP size and optical emission, enabling size-dependent tunable PL for UV optoelectronic applications.
References:
1. K.A. Alim, V.A. Fonoberov, M. Shamsa, A.A. Balandin, “Micro-Raman investigation of optical phonons in ZnO nanocrystals”, Journal of Applied Physics, vol. 97, pp. 124313, 2005.
2. G. Yang, Laser Ablation in Liquids: Principles and Applications in the Preparation of Nanomaterials, Pan Stanford, 2012.
3. Gyan Prakash Bharti and Alika Khare, “Quenching of visible photoluminescence and observation of two photon absorption-induced photoluminescence in pulsed laser deposited Zn1−xTixO (0.000 ⩽ x ⩽ 0.050) thin films”, Journal of Physics D: Applied Physics vol. 52, pp. 015103 , 2019.
