Luminescence Properties of Dual Valence Eu Doped Nano-crystalline BaF2 Embedded Glass-ceramics and Observation of Eu2+ → Eu3+ Energy Transfer |
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Authors: | Kaushik Biswas Atul D Sontakke R Sen K Annapurna |
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Institution: | (1) Glass Science and Technology Section, Central Glass and Ceramic Research Institute, Council of Scientific and Industrial Research, 196, Raja S.C. Mullick Road, Kolkata, 700 032, India; |
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Abstract: | Europium doped glass-ceramics containing BaF2 nano-crystals have been prepared by using the controlled crystallization of melt-quenched glasses. X-ray diffraction and
transmission electron microscopy have confirmed the presence of cubic BaF2 nano-crystalline phase in glass matrix in the ceramized samples. Incorporation of rare earth ions into the formed crystalline
phase having low phonon energy of 346 cm−1 has been demonstrated from the emission spectra of Eu3+ ions showing the transitions from upper excitation states 5DJ (J = 1, 2, and 3) to ground states for the glass-ceramics samples. The presence of divalent europium ions in glass and glass-ceramics
samples is confirmed from the dominant blue emission corresponding to its 5d-4f transition under an excitation of 300 nm. Increase in the reduction of trivalent europium (Eu3+) ions to divalent (Eu2+) with the extent of ceramization is explained by charge compensation model based on substitution defect mechanisms. Further,
the phenomenon of energy transfer from Eu2+ to Eu3+ ion by radiative trapping or re-absorption is evidenced which increases with the degree of ceramization. For the first time,
the reduction of Eu3+ to Eu2+ under normal air atmospheric condition has been observed in a BaF2 containing oxyfluoride glass-ceramics system. |
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