when Mn and Mg are co-doped in ZnS as host matrix, there is green emission observed in PL spectra.
the band gap is decreases while dopent (like Co, Mn) concentration it's result red shift in PL spectrum.
How the addition of co-dopants can decrease or increase the band gap?
Is it because of formation of more no, of defects with the addition of external impurities? what about its effect with respect to intensity? Addition of co-dopants can also enhance/decrease the luminescence intensity.. Please correct me if i am wrong..
Dopants will introduce new states within the bandgap. Radiative recombination from these states could lead to photoluminescence. ZnS doped with Mn however usually shows orange color.
Green emotions are believed to be due to the intrinsic defects in the ZnS nano particles, for example, O- vacancies or Zn interstitials, etc. For more details, you may refer to some of our papers on the topic.
--- P D Sahare
Amit, could you please share a few of those papers. I worked with the system over 10 years ago and at that time it was well established that Mn doping leads to orange-red emission, and we observed the same. On the other hand as Prof. Sahare pointed out, it is well known that surface defects introduce extra states within the BG (intrinsic effect) lead to a green emission
Amit, maybe I am wrong, but the message I got from the paper you attached (second one) was that Mn doping leads to a 590 nm emission, as we have observed and is generally known in the literature. All the emissions in the blue-green wavelengths (445, 475 and 520 nm) are attributed to defects, as pointed out by Prof. Sahare.
The first paper was lacking data to clearly identify the origin of green emission to dopant states. Actually I am totally confused by that paper, right from figure 1. The peak indexing of ZnS nanoparticles have nothing in common with bulk ZnS.
Since photoluminescence is due to electron relaxations where the exact pathway is essentially random and the lifetimes determine the probability (faster is more probable), so it is possible to have doped ZnS that are still relaxing via defect states due to shorter lifetimes (I haven't compared the lifetimes).
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