The UV-VIS spectrum of the CdS nanocomposite is shown in Figure 1. It shows a single, sharp absorption

edge at 482 nm, which corresponds to the quantum shifted excitonic absorption energy in the nano compositeCdS. The graph of the absorbance against energy (hν) was plotted and the energy gap E_g was obtained by extrapolating the straight line path to the energy axis. The value obtained was 2.57 eV (482 nm).

This shows that there is shift to higher energy when compared with band gap of thin film. This quantum effect has been observed for most semiconductor materials [35] [36] .

The average nano particle radius (R) was determined from the difference in the energy band gap of the nanoparticles and the bulk crystal of CdS using the following equation [37] .

where h is the Planck’s Constant

are the effective masses of the electrons and hole in CdS

[38] . ΔE_g is difference between the energy band gap of the nanoparticle and the bulk crystal. The particle radius was found to be 7.3 nm. The obtained particle size is similar to the value obtained Stroyuk et al. [39] .

The energy dispersive x-ray (EDS) spectrum (Figure 2) shows the presence of Cd, S, Na, Cl, and C, the presence of sodium and chlorine may be attributed to NaCl which were incorporated during synthesis. The stoichiometric ratio of Cd to S is found to be Cd₂₃S₂₀. The observed ratio is in agreement with that reported by Favero et al. [40] . This shows that the surface atoms tend to migrate to the sub-surface layer i.e. the nanoparticles are sulphur terminated [40] . This also agrees with the work of Winkler and coworkers [41] .

The PIXE analysis (Figure 3) also shows the elemental composition of the composite. It confirms the presence of expected Cd and S. It also reveals a lot of impurities that hitherto were not revealed by the EDS.

These impurities in some cases could be advantageous depending on the application. They could be an active or quenching center. For example the presence of Manganese as impurity in CdS is known to have effect on the optical properties especially as it relates to the photoluminescence properties of the nanoparticles. The EDS limitation may be due to continuous bremsstrahlung background caused by primary and secondary radiation. However, the stoichiometric ratio of Cd to S could not be determined.

The HRTEM micrograph of the nanocomposite (Figure 4) clearly shows the presence of the nanoparticles which are well dispersed as individual entities (completely capped) and the particle size are between 2 - 10 nm. The mean sizes of the CdS nanoparticles determined from HRTEM approached those estimated from the UV absorption threshold. The micrograph of the SEM (not shown) also reveals the presence of the nanocomposite, however, the CdS nanoparticles appear in form of a cluster and the particles sizes are not well resolve. This may be due to resolution limit of the SEM used.

The room temperature UV-Vis absorption spectrum of the ZnS composite is shown in Figure 5. The extrapolation of the straight line region of the plot of the absorbance against wavelength to zero shows that the absorption edge occurs at 325 nm which corresponds to energy of 3.82 eV. This when compared with bulk ZnS with energy band gap of 3.65 eV (340 nm), the absorption spectrum of the ZnS composite (325 nm) showed a blue shift towards high energy, indicating that the ZnS nanocomposites were quantum-confined.

The average nano particle radius (R) was also determined from difference in the energy band gap of the nanoparticles and the bulk crystal of ZnS using Equation (1). The effective masses of the electrons and hole of ZnS are 0.22 m_e and 0.23 m_e respectively [42] [43] . The particle radius was calculated and found to be 8.88 nm.

The EDS (energy dispersive X-ray) spectrum of the products revealed that the nanocomposite comprised of Zn, S and other impurities. The impurities are sodium and chlorine which were incorporated during the synthesis

process. Elemental analysis reveals the atomic percentages of Zn and S are 58.3% and 41.7% respectively, which suggests S vacancies in ZnS nanocomposite. This quite agrees with what was reported by Yue et al. [44] .

The PIXE micrograph of ZnS is shown in Figure 6. It shows the elemental composition of the composite and relative concentration of the element present. It confirmed the presence of Zn, S as well as other impurities to the level of part per million. Majorities of the impurities were Na, Cl. This may be due to by-product (NaCl) formed in the as prepared nanocomposites [45] . The presence of carbon was also confirmed which stem from the binder. Other impurities present were Mn, Ni, Cu, Fe, Mo, Sr and Ba. As shown in Figure 6 these impurities might have their origin in the starting material.

The SEM micrograph of ZnS composite taken under 975× magnifications is shown in Figure 7. The micrograph shows that the composite are in form of clusters, hence, the grain size could not be determined. The average cluster size is less than 20 µm. This implies that the growth of the composite is mostly considered to be the result of the surface aggregation of colloidal particles (cluster-by-cluster growth) [46] [47] . The single nanocrystal cannot be clearly resolved due to the system resolution limit, but the presence of small nanocluster is apparent.

The plot of the absorbance against wavelength (Figure 8) shows that the absorption edge of CdZnS occurs at

446 nm which corresponds to 2.78 eV. This value when compared with band gap of the CdS (2.4 eV) and ZnS (3.65 eV) shows that the obtained band gap lies within the expected value. The shift of absorption edge toward shorter wavelength indicates that increasing Zn atomic ratio gives rise to increase in energy gap (Eg). This observation is in agreement with the work Kumara et al. [48] , where it was reported that the band gap of CdZnS lies within the band gap of CdS and ZnS.

The EDS spectrum of the nano composite of CdZnS was shown in Figure 9. The spectral shows the presence of cadmium, zinc, sulphur, chlorine and carbon. The presence of chlorine may be due to residues of the byproduct from the synthesis while carbon originated from the binder.

The stoichiometry ratio of Cd:Zn:S was found to 32.0% Cd, 34.6% Zn and 33.4% S . While Figure 10 shows the PIXE micrograph of the composites, it reveals the elemental composition of the composite namely Cd, Zn and S. It also reveals a lot of impurities that hitherto were not revealed by the EDS. These impurities include Fe, Mn, Cl, Cu, Br, Sr, Mo and Ba. The presence of the impurities may have stem from starting reagent and residues of the reactant.

The SEM micrograph of CdZnS nanocomposite under 1000× magnification is shown in Figure 11. The general surface morphology shows that the particles are in cluster form under 1000× magnification. A closer look at the micrograph shows that the clusters exhibited a needle like shape with average cluster size less than 10 µm. This confirmed that the particles are in nano range.