In one of my systems the P.L intensity of Eu(III) ions is nearly same for the base glass and glass-ceramics (GC) heat-treated upto a certain time duration. An abrupt rise in P.L intensity is noticed for the GC fabricated at maximum duration of time along with increase in lifetime. Does degree of crystallinity or microstructure morphologies play a role here?? Please cite a clear scientific explanation or suggest any reference..
Dear Anirban,
It is generally seen that with increase in heating temperature of the glass, the crystallinity does appears and also increases with annealing time and temperature. This makes PL intensity also increases. This is not only true in Glass- Glass Ceramics but can also be seen in Crystalline materials.
Similar effect is also observed in the following article
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However there are few contradictory reports where they observed, with increase in annealing temperature the PL intensity decreases. This may be due crystallinity, as the report states that there are different phases of Alpha/Gamma TeO2 and also TiTe3O8. The dopant Eu3+ may have different emission intensity in these phases. Therefore in this case the presence of different phases affects the PL intensity.
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Thank you for you answer. But in my system the glass-ceramics are fabricated by isothermal treatment by increasing the heat-treatment duration. And ofcourse my system contain two different phases: a noncentrosymmetric and a centrosymmetric phase..Reduction of Eu3+ to Eu2+ also cannot be considered as I did not get any evidence as such in absorption and excitation-emission spectra..
How you come to know that your samples two different phases: a noncentrosymmetric and a centrosymmetric phase??
Also without reducing atmosphere Eu3+ cannot be converted into Eu2+. To get Eu2+ you may have to anneal your samples in reducing atmosphere.
Through XRD analysis. And there are papers in literature which report reduction of Eu3+ to Eu2+ in normal conditions/air atmospheres also...
Dear Anirban,
There can be many reasons for the observation of luminescence enhancement in glass ceramic sample over the precursor glass sample. Normally, the glass is less denser than the corresponding crystalline matrix, so when it tend to crystallize, the change in relative crystal field effect on the dopant ion turns decisive in luminescence outputs. Also, the changes in the emission peak width and branching ratio also need to be considered in evaluating the intensity trends. The reverse effect is also possible due to increase in quenching effects, defect formation, etc. It is sample specific. Be careful if the glass-ceramic becomes semi-transparent or opaque, as then the surface scattering and reflection becomes more important factors.