Abstract
Bi3+ (y = 0–15 at.%) sensitized CaWO4:Eu3+ (5 at.%) red emitting phosphors were successfully prepared by hydrothermal method. All the samples generated intense red emission under the excitation at 393 and 464 nm. The incorporation of Bi3+ in CaWO4 does not induce any interference among the optical properties of WO42− and Bi3+. The sensitization with Bi3+ in CaWO4:Eu3+ leads to the enhancement of ∼393 nm (7F0 → 5L6) and ∼464 nm (7F0 → 5D2) absorption peak of Eu3+. At optimal concentration of Bi3+, the enhancement is 5 and 10 for ∼393 nm (7F0 → 5L6) and ∼464 nm (7F0 → 5D2), respectively. A further enhancement in emission at optimized Bi3+ concentration by a factor of ∼5.8 and ∼22 under the respective excitation of 393 and 464 nm is observed after annealing the samples at 500 °C. The energy transfer efficiency from Bi3+ to Eu3+ was improved from 75% to 95% post annealing. The energy transfer process is observed to be occurred mainly due to dipole-dipole interactions. The CIE chromaticity coordinates reveal the nearly 100% saturation of red color emission.
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