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Effect of annealing temperature on the luminescence of Ce1−x PO4: Tb x 3+ nanocrystals: A novel theoretical model and experimental verification

Sisira, S., Alexander, Dinu, Thomas, Kukku, Biju, P. R., Unnikrishnan, N. V., Joseph, Cyriac
Journal of materials science 2018 v.53 no.2 pp. 1380-1394
X-ray diffraction, annealing, cerium, crystallization, equations, luminescence, microwave treatment, models, nanocrystals, optical properties, phosphates, scanning electron microscopy, sol-gel processing, temperature, thermal stability, transmission electron microscopy
Terbium-doped cerium phosphate nanocrystals are successfully synthesized through microwave-assisted sol–gel method and are annealed at different temperatures for detailed investigation on structural and optical properties. The structural characterization carried out using X-ray diffraction analysis confirmed that all the samples are crystallized in monoclinic structure having chemical formula CePO₄ and revealed the thermal stability of the synthesized samples. A novel theoretical model is proposed to investigate the influence of annealing temperature on Tb³⁺ by analyzing I₄/I₃—annealing temperature plot in which two regions are distinguished as above and below the crystallization temperature. A generalized equation derived in terms of rate constants for I₄/I₃ helps to frame four distinct cases describing the role of different radiative and nonradiative relaxations in the Tb³⁺ luminescence from ⁵D₃ and ⁵D₄ levels. The subsequent evaluation of each case described the role of defects, cross-relaxation and multiphonon relaxation in the variation of I₄/I₃ with annealing temperature and verified by the experimentally observed data with the help of TEM, FESEM, TGA and decay analysis.