ZnS nanocrystals were prepared by the chemical co-precipitation method. The effect of annealing temperature
(Ta) on the morphological, structural and optical absorption behavior was investigated using x-ray diffraction
(XRD), high resolution transmission electron microscope (HRTEM), UV-vis spectroscopy, selected area electron
diffraction (SAED) and Fourier transform infrared (FTIR) spectroscopy. Analysis of XRD patterns for as prepared
and annealed samples showed that, increasing Ta leads to an increase in the crystallite size (D) from 2.67 to
19.6 nm. It is noticed that the obtained values of lattice parameters from HRTEM Images and SAED patterns are
in good agreement with that deduced from XRD analysis. Furthermore, annealing process at 600 oC and 700 oC
results, in complete phase transformation from as prepared ZnS cubic structure to ZnO hexagonal structure.
Analysis of the XRD patterns, SAED, HRTEM and FTIR confirm this phase transition. Analysis of the optical
absorption spectra indicates noticeable decrease in the direct band gap from 4.70 to 3.22 eV with
increasing Ta. This behavior is attributed to the enhancement in crystallinity and the increase in particle size of ZnS nanoparticles. Moreover, UV photo-induced effect on the optical absorption edge was studied.

ZnS nanocrystals were prepared by the chemical co-precipitation method. The effect of annealing temperature
(Ta) on the morphological, structural and optical absorption behavior was investigated using x-ray diffraction
(XRD), high resolution transmission electron microscope (HRTEM), UV-vis spectroscopy, selected area electron
diffraction (SAED) and Fourier transform infrared (FTIR) spectroscopy. Analysis of XRD patterns for as prepared
and annealed samples showed that, increasing Ta leads to an increase in the crystallite size (D) from 2.67 to
19.6 nm. It is noticed that the obtained values of lattice parameters from HRTEM Images and SAED patterns are
in good agreement with that deduced from XRD analysis. Furthermore, annealing process at 600 oC and 700 oC
results, in complete phase transformation from as prepared ZnS cubic structure to ZnO hexagonal structure.
Analysis of the XRD patterns, SAED, HRTEM and FTIR confirm this phase transition. Analysis of the optical
absorption spectra indicates noticeable decrease in the direct band gap from 4.70 to 3.22 eV with
increasing Ta. This behavior is attributed to the enhancement in crystallinity and the increase in particle size of ZnS nanoparticles. Moreover, UV photo-induced effect on the optical absorption edge was studied.

ZnS nanocrystals were prepared by the chemical co-precipitation method. The effect of annealing temperature
(Ta) on the morphological, structural and optical absorption behavior was investigated using x-ray diffraction
(XRD), high resolution transmission electron microscope (HRTEM), UV-vis spectroscopy, selected area electron
diffraction (SAED) and Fourier transform infrared (FTIR) spectroscopy. Analysis of XRD patterns for as prepared
and annealed samples showed that, increasing Ta leads to an increase in the crystallite size (D) from 2.67 to
19.6 nm. It is noticed that the obtained values of lattice parameters from HRTEM Images and SAED patterns are
in good agreement with that deduced from XRD analysis. Furthermore, annealing process at 600 oC and 700 oC
results, in complete phase transformation from as prepared ZnS cubic structure to ZnO hexagonal structure.
Analysis of the XRD patterns, SAED, HRTEM and FTIR confirm this phase transition. Analysis of the optical
absorption spectra indicates noticeable decrease in the direct band gap from 4.70 to 3.22 eV with
increasing Ta. This behavior is attributed to the enhancement in crystallinity and the increase in particle size of ZnS nanoparticles. Moreover, UV photo-induced effect on the optical absorption edge was studied.

Capping free Zinc Sulphide nanoparticles were synthesis from aqueous solutions of Zinc Chloride (ZnCl2) and Sodium Sulphide (Na2S) in air at 70oC by co-precipitation method. The as-prepared and annealed samples were characterized by X-ray diffraction (XRD), UV-Vis absorption, scanning electron microscope (SEM), transmission electron microscope (TEM) and selected area electron diffraction (SAED). Analysis of XRD pattern indicates that the as prepared and annealed samples up to 300oC ZnS nano-crystallites have cubic zinc blend structure. Furthermore, annealing at 550oC,
results in partial conversion of the initially cubic ZnS, to ZnS and ZnO Hexagonal phases as revealed by XRD patterns.SAED pattern for as-prepared ZnS reveals the polycrystalline nature. Furthermore, the lattice parameters determined from(XRD) and (SAED) patterns are in good agreement. Annealing of the ZnS nanoparticles in air in the temperature range,
150 – 550oC, leads to the increase in crystallite size from 2.14 to 18 nm accompanied by decrease in optical band gap(Egopt) from 3.98 to 3.3eV, for the as prepared and sample annealed at 550oC respectively. Analysis of TEM and SEM Images indicates that the ZnS nanoparticles tend to be nearly spherically shaped with narrow size distribution. Different times UV irradiation of ZnS aqueous solution results in increase in optical energy gap with the irradiation time. The observed photo brightening is explained in terms of the formation of ZnSO4 passivation layer via photon-assisted chemical reaction.

Capping free Zinc Sulphide nanoparticles were synthesis from aqueous solutions of Zinc Chloride (ZnCl2) and Sodium Sulphide (Na2S) in air at 70oC by co-precipitation method. The as-prepared and annealed samples were characterized by X-ray diffraction (XRD), UV-Vis absorption, scanning electron microscope (SEM), transmission electron microscope (TEM) and selected area electron diffraction (SAED). Analysis of XRD pattern indicates that the as prepared and annealed samples up to 300oC ZnS nano-crystallites have cubic zinc blend structure. Furthermore, annealing at 550oC,
results in partial conversion of the initially cubic ZnS, to ZnS and ZnO Hexagonal phases as revealed by XRD patterns.SAED pattern for as-prepared ZnS reveals the polycrystalline nature. Furthermore, the lattice parameters determined from(XRD) and (SAED) patterns are in good agreement. Annealing of the ZnS nanoparticles in air in the temperature range,
150 – 550oC, leads to the increase in crystallite size from 2.14 to 18 nm accompanied by decrease in optical band gap(Egopt) from 3.98 to 3.3eV, for the as prepared and sample annealed at 550oC respectively. Analysis of TEM and SEM Images indicates that the ZnS nanoparticles tend to be nearly spherically shaped with narrow size distribution. Different times UV irradiation of ZnS aqueous solution results in increase in optical energy gap with the irradiation time. The observed photo brightening is explained in terms of the formation of ZnSO4 passivation layer via photon-assisted chemical reaction.

Capping free Zinc Sulphide nanoparticles were synthesis from aqueous solutions of Zinc Chloride (ZnCl2) and Sodium Sulphide (Na2S) in air at 70oC by co-precipitation method. The as-prepared and annealed samples were characterized by X-ray diffraction (XRD), UV-Vis absorption, scanning electron microscope (SEM), transmission electron microscope (TEM) and selected area electron diffraction (SAED). Analysis of XRD pattern indicates that the as prepared and annealed samples up to 300oC ZnS nano-crystallites have cubic zinc blend structure. Furthermore, annealing at 550oC,
results in partial conversion of the initially cubic ZnS, to ZnS and ZnO Hexagonal phases as revealed by XRD patterns.SAED pattern for as-prepared ZnS reveals the polycrystalline nature. Furthermore, the lattice parameters determined from(XRD) and (SAED) patterns are in good agreement. Annealing of the ZnS nanoparticles in air in the temperature range,
150 – 550oC, leads to the increase in crystallite size from 2.14 to 18 nm accompanied by decrease in optical band gap(Egopt) from 3.98 to 3.3eV, for the as prepared and sample annealed at 550oC respectively. Analysis of TEM and SEM Images indicates that the ZnS nanoparticles tend to be nearly spherically shaped with narrow size distribution. Different times UV irradiation of ZnS aqueous solution results in increase in optical energy gap with the irradiation time. The observed photo brightening is explained in terms of the formation of ZnSO4 passivation layer via photon-assisted chemical reaction.

Monodispersed ZnS nanoparticles (NPs) were prepared by the chemical precipitation method. Thermally induced structural, morphological and optical changes have been investigated using x-ray diffraction, high-resolution transmission electron microscopy, optical absorption, photoluminescence (PL), and Fourier transform infrared and Raman spectroscopy. It was found that D increases with increasing annealing temperature (T a). The onset of the ZnS phase transition from cubic to hexagonal structure takes place at 400 °C, while cubic ZnS transforms into hexagonal ZnO via thermal oxidation in air at 600 °C. It is also noted that increasing T a results in the red shift of the optical band gap (Eg ) and the thermal bleaching of exciton absorption. The PL spectrum of as-prepared ZnS nanopowder shows UV emission bands at 363 and 395 nm and blue and green emission at 438 and 515 nm, respectively. With increasing T a up to 500 °C, these bands were quenched and red-shifted. In addition, the UV irradiation effects on colloidal ZnS NPs were investigated. UV irradiation at a dose  <13 J cm−2 leads to a decrease in D, the blue shift of Eg and the enhancement of PL intensity. This behavior was explained in terms of surface modification by photopolymerization, the formation of a ZnSO4 passivation laye, as well as the reduction of D by photo-corrosion. At a UV irradiation dose  <13 J cm−2 both Eg and D did not change and PL intensity was quenched, which were caused by the creation of nonradiative surface states by the photodegradation of the capping agent and photo passivated layer. The mechanism of the PL emission process in ZnS NPs was discussed and an energy band diagram was proposed.

Monodispersed ZnS nanoparticles (NPs) were prepared by the chemical precipitation method. Thermally induced structural, morphological and optical changes have been investigated using x-ray diffraction, high-resolution transmission electron microscopy, optical absorption, photoluminescence (PL), and Fourier transform infrared and Raman spectroscopy. It was found that D increases with increasing annealing temperature (T a). The onset of the ZnS phase transition from cubic to hexagonal structure takes place at 400 °C, while cubic ZnS transforms into hexagonal ZnO via thermal oxidation in air at 600 °C. It is also noted that increasing T a results in the red shift of the optical band gap (Eg ) and the thermal bleaching of exciton absorption. The PL spectrum of as-prepared ZnS nanopowder shows UV emission bands at 363 and 395 nm and blue and green emission at 438 and 515 nm, respectively. With increasing T a up to 500 °C, these bands were quenched and red-shifted. In addition, the UV irradiation effects on colloidal ZnS NPs were investigated. UV irradiation at a dose  <13 J cm−2 leads to a decrease in D, the blue shift of Eg and the enhancement of PL intensity. This behavior was explained in terms of surface modification by photopolymerization, the formation of a ZnSO4 passivation laye, as well as the reduction of D by photo-corrosion. At a UV irradiation dose  <13 J cm−2 both Eg and D did not change and PL intensity was quenched, which were caused by the creation of nonradiative surface states by the photodegradation of the capping agent and photo passivated layer. The mechanism of the PL emission process in ZnS NPs was discussed and an energy band diagram was proposed.

Monodispersed ZnS nanoparticles (NPs) were prepared by the chemical precipitation method. Thermally induced structural, morphological and optical changes have been investigated using x-ray diffraction, high-resolution transmission electron microscopy, optical absorption, photoluminescence (PL), and Fourier transform infrared and Raman spectroscopy. It was found that D increases with increasing annealing temperature (T a). The onset of the ZnS phase transition from cubic to hexagonal structure takes place at 400 °C, while cubic ZnS transforms into hexagonal ZnO via thermal oxidation in air at 600 °C. It is also noted that increasing T a results in the red shift of the optical band gap (Eg ) and the thermal bleaching of exciton absorption. The PL spectrum of as-prepared ZnS nanopowder shows UV emission bands at 363 and 395 nm and blue and green emission at 438 and 515 nm, respectively. With increasing T a up to 500 °C, these bands were quenched and red-shifted. In addition, the UV irradiation effects on colloidal ZnS NPs were investigated. UV irradiation at a dose  <13 J cm−2 leads to a decrease in D, the blue shift of Eg and the enhancement of PL intensity. This behavior was explained in terms of surface modification by photopolymerization, the formation of a ZnSO4 passivation laye, as well as the reduction of D by photo-corrosion. At a UV irradiation dose  <13 J cm−2 both Eg and D did not change and PL intensity was quenched, which were caused by the creation of nonradiative surface states by the photodegradation of the capping agent and photo passivated layer. The mechanism of the PL emission process in ZnS NPs was discussed and an energy band diagram was proposed.

Monodispersed ZnS nanoparticles (NPs) were prepared by the chemical precipitation method. Thermally induced structural, morphological and optical changes have been investigated using x-ray diffraction, high-resolution transmission electron microscopy, optical absorption, photoluminescence (PL), and Fourier transform infrared and Raman spectroscopy. It was found that D increases with increasing annealing temperature (T a). The onset of the ZnS phase transition from cubic to hexagonal structure takes place at 400 °C, while cubic ZnS transforms into hexagonal ZnO via thermal oxidation in air at 600 °C. It is also noted that increasing T a results in the red shift of the optical band gap (Eg ) and the thermal bleaching of exciton absorption. The PL spectrum of as-prepared ZnS nanopowder shows UV emission bands at 363 and 395 nm and blue and green emission at 438 and 515 nm, respectively. With increasing T a up to 500 °C, these bands were quenched and red-shifted. In addition, the UV irradiation effects on colloidal ZnS NPs were investigated. UV irradiation at a dose  <13 J cm−2 leads to a decrease in D, the blue shift of Eg and the enhancement of PL intensity. This behavior was explained in terms of surface modification by photopolymerization, the formation of a ZnSO4 passivation laye, as well as the reduction of D by photo-corrosion. At a UV irradiation dose  <13 J cm−2 both Eg and D did not change and PL intensity was quenched, which were caused by the creation of nonradiative surface states by the photodegradation of the capping agent and photo passivated layer. The mechanism of the PL emission process in ZnS NPs was discussed and an energy band diagram was proposed.