Keywords:Amorphous calcium silicate Calcium silicate hydrate Energy transfer Luminescent color Eu 3 þ and Tb 3 þ codoped a b s t r a c t A Eu 3 þ , Tb 3 þ codoped amorphous calcium silicate phosphor was prepared by heating a Eu 3 þ , Tb 3 þ codoped calcium silicate hydrate phosphor formed by liquid-phase reaction for 30 min at 900 1C.The excitation peak wavelength of the resulting phosphor was 379 nm and the emission peak wavelengths were at 542 nm, attributed to the 5 D 4 -7 F 5 transition of Tb 3 þ , and at 613 mm, attributed to the 5 D 0 -7 F 1 transition of Eu 3 þ . The intensity ratio of the two peaks could be freely controlled by varying the Eu/Tb atomic ratio of the Eu 3 þ , Tb 3 þ codoped amorphous calcium silicate phosphor, allowing light to be emitted over a wide range from green to red. It was clarified that electron transfer from Tb 3 þ to Eu 3 þ is occurring.

The excitation wavelength of conventional Tb 3+ -activated phosphor is near 270 nm. This study describes novel green-emitting Tb 3+ -activated amorphous calcium silicate by ultraviolet excitation at 378 nm. The Tb 3+ -activated amorphous calcium silicate was prepared by heating a sample of Tb 3+ -activated calcium silicate hydrate (CSH) at 900• C for 30 minutes. The emission wavelength of the resulting phosphor was 544 nm. The optimum excitation wavelength within the range 300-400 nm was 378 nm. The Tb 3+ -activated amorphous calcium silicate emitted green by ultraviolet irradiation. The optimum initial Tb/Ca atomic ratio of this phosphor was about 0.5. A mechanism for the action of the phosphor is proposed, in which Tb 3+ ions existing in the layer of the CSH lead to loss of water molecules and OH groups.

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