The effect of ultraviolet irradiation on the optical properties of ZnS: Mn synthesized by hydrothermal method and using thioglycolic acid

Photo-Activated Phosphorescence of Ultrafine ZnS:Mn Quantum Dots: On the Lattice Strain Contribution

“…In almost all these studies, an intensity increase of the whole photoluminescence spectra is reported. In other words, the intensities of both the broad blue/green emission around 450 nm, which is also observed in undoped nanocrystalline ZnS NPs and usually ascribed to a defect-related emission of surface blende lattice, and the orange emission around 580 nm, attributed to the spin-forbidden [MnS 4 ] 6– transition, increase after UV irradiation. − Moreover, in the same works, the relative intensity increase of the former appeared to be stronger. , These results support the passivation mechanism of surface states that strongly increases the relative contribution of radiative recombination of the delocalized charge carriers by countering that effect of trapping surface states. In the case of orange emission, once the excitation energy is localized on the Mn 2+ centers in their excited state, surface passivation is less important.…”

“…They invoked a surface passivation effect as a consequence of UV curing of the residual dioctyl sulfosuccinate ligands. Thai et al investigated the same phenomenon on hydrothermally prepared NPs in the presence of thioglycolic acid, which by thermal decomposition provides the required sulfide ions for metal sulfide precipitation and glycolic acid moieties, of which hydroxyl groups coordinate the particle surface during the particle growth. They supposed that UV irradiation favors a surface photochemical process, for which a change of the α-hydroxyl acetic acid creates surface passive polymeric shells able to prevent nonradiative recombination.…”

“…Interestingly, differently from all previous studies, they found that the increase of the yellow-orange emission intensity was stronger than that of the blue-green one. 24 ■ METHODS Chemicals. Zinc(II) acetate, manganese(II) acetate (Sigma-Aldrich, 99.9%), thioacetamide (Sigma-Aldrich, ≥99%), and absolute ethanol (VWR, >99.5%), were purchased and used as received.…”

“…Rather than a passivation effect, we assert that this outer layer induces local strains on the emitting [MnS 4 ] 6– centers, thus partially lifting the selection rules associated with the transition between the 4 T 1 and 6 A 1 molecular states. The idea of strain effects on the phosphorescence enhancement of ZnS:Mn particles was already suspected, although less highlighted compared to passivation effect, by Thai et al These authors also reported a photoluminescence intensity increase over UV irradiation time on their particles synthesized from thioglycolic acid HSCH 2 CO 2 H and initial chemicals Zn­(CH 3 CO 2 ) 2 ·2H 2 O, Mn­(CH 3 CO 2 ) 2 ·4H 2 O by a hydrothermal method. Interestingly, differently from all previous studies, they found that the increase of the yellow-orange emission intensity was stronger than that of the blue-green one …”