Structural, optical and photoluminescence properties of ZnS: Cu nanoparticle thin films as a function of dopant concentration and quantum confinement effect

Abstract

Thin films of ZnS: Cu nanoparticles were deposited in chemical bath by a pH controlled solution synthesis technique. The copper concentration was varied from 0 to 0.1M%. XRD and SEM indicated variations in diffracted intensity and morphology with Cu concentration. The PL spectrum of the undoped ZnS nanoparticles showed emission peaks at 393 and 432nm that could be attributed to the intrinsic defect states of ZnS nanoparticles. For ZnS: Cu samples three peaks in the range of 390nm, 480nm and 525nm were observed. With increase in Cu concentration from 0.001 to 0.1M%, the peak position of 480nm and 525nm did not change, whereas 390nm peak red shifted to longer wavelength region to 422nm. In addition, it was found that the overall photoluminescence intensity reached maximum at 0.01M% and quenched with further increase in Cu concentration. Enhancement of blue and green light emission by seven and twenty fivefold respectively compared to undoped ZnS was observed in ZnS: Cu with optimal dopant concentration. Time resolved decay of photoluminescence showed faster decay for 390 -420nm purple/ blue emission compared to green (525nm) Cu related emission which is in the microsecond time scale. Optical absorption measurements indicate enhancement of band gap (3.89eV) for undoped ZnS suggesting the quantum confinement effect in the developed nanoparticles of size below the Bohr diameter.

Surface plasmon resonance in nanostructured Ag incorporated ZnS films

“…8(b) and TABLE I. The observed blue shift of band gap energy with increase in Ag incorporation can be due to quantum confinement effect due to decrease in the size of the crystallites in the films 45,46 as revealed by XRD, AFM and SEM analysis. Other subordinate effects such as polaron, strain, size and imperfection may also leads to a widening of the band gap.…”

Luminescence and Morphological Kinetics of Functionalized ZnS Colloidal Nanocrystals

“…Photoluminescence properties of ZnS have received special attention because of emission in different visible bands due to dopant ions in host matrices. The blue luminescence of ZnS host and orange luminescence due to the 4 T 1 -6 A 1 transition of Mn 2+ ions excited via energy transfer from the host ZnS have been reported by various researchers [13,14]. At nanoregime, the potential advantages have been occurred in ZnS due to the spatial confinement of photoexcited electrons and holes that modify its optical and other related properties.…”

Controlled synthesis of Eu2+ and Eu3+ doped ZnS quantum dots and their photovoltaic and magnetic properties

“…[7][8][9][10][11] In addition to blue luminescence of ZnS, it is known that, e.g., see Ref. 12, various dopants result in different emission bands such as the orange luminescence in ZnS:Mn nanoparticles attributed to 4 T 1 -6 A 1 transition of Mn 2+ ions, and the green emission from the characteristic 4f 6 5d 1 -4f 7 transition of Eu 2+ in ZnS:Eu QDs. 9,13,14 Quantum confinement can affect the band structure of doped QDs and the relative energy levels of the dopants.…”