I observe the g-shift to lower values in EPR spectrum after irradiating. is it due to the change of state for host material (like, W6+ to W5+,......)? or it is due to the reduction of particle size? Any reference...
Dear Asif,
this is an interesting question.
First of all, the g value reflects the distribution of the unpaired electron(s).
You can read from the g value e.g. if the unpaired electrons reside essentially on heavy atoms (low g) or light atoms (higher g), if the electrons are more localised (low g) or delocalised (high g), and it reflects the spin state: S = 1/2 or I or 3/2 etc.
For your particles: The g does not depend on the particle size.
Also, W6+ is diamagnetic. If you start from this, irradiation might lead to W5+ (S = 1/2) but might also go further to W4+ (probably S = 1). So in your case the lowering of the g values (I guess there is more than one, right?) might be due to the oxidation state.
However, If you do not provide more details about your material, any interpretation is a bit like stirring the bottom of your coffee beaker and trying to read the future out of it. The same for your request for references.
Axel Klein
Thanks for your valuable response. I just write W+... as an example to know about the state change. Actually, I am working on Fe-doped TiO2. The peak is shifting to the left lowering the g value. From 318.435mT to 318.431mT. So, g-shift to lower is attributed due tp Ti+4 to Ti3+ or Fe3+ to Fe2+?
Dear Asif,
318.435 to 318.431 is not a big shift, insn't ?
Are these two measurements with different frequencies (from measurement to measurement, the frquency shifts slightly) or did you irradiate during the EPR measurement (at a constant frequency)?
Asif Ali Haider Hello Asif, could you show your EPR spetra here? Presumably you use X-band CW spectrometer and study transition metal ions powder sample.
This is an intriguing subject, in this scenery, recently we find in our data, thermal treated ZnO NPs have a progressive change in one of the g values (g2).If we think about this system, the type of defects that can given an EPR signal is the unpaired electrons (electrons trapped in a type of defect). Same to my data, two peaks are observed in the reference (DOI 10.1002/pssr.201004450) and the first g1 ~ 2.004 is attributed to the surface defects, and the g2~ 1.960 is commonly attributed to singly ionized oxygen vacancy defects. The last g shifts as the thermal annealing temperature increases. My question what would be the mechanism of this change?
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