12CaO · 7Al2O3 doped with lanthanide is characterized by remarkable and technologically important up-conversion emission. However, the low up-conversion efficiency still remains the main limitation for practical applications. To improve the efficiency, bivalent alkaline earth ions (Mg2+, Sr2+, Ba2+)-tridoped Tm3+/Yb3+/12CaO · 7Al2O3 were synthesized through a high-temperature solid-state reaction. The up-conversion luminescence properties of the samples were investigated by X-ray diffraction, fluorescence spectral measurement pump power, and fluorescence decay curves. The luminescence intensity of samples was significantly enhanced by bivalent alkaline earth ions. 12CaO · 7Al2O3 doped with Sr2+ ions has stronger effects on up-conversion enhancement, which is better than Mg2+ and Ba2+. The up-conversion emission intensity was enhanced by 318 times and the red emission intensity by 218 times with 10 mol% Sr2+ ion. Additionally, the blue and red up-conversion emission peaks at 475 and 650 nm corresponding to energy transitions of 1G4 → 3H6 and 1G4 → 3F4, 3F2 → 3H6 were characterized using steady-state rate equations.
A novel multicolor-tunable lanthanide doped 12CaO·7Al 2 O 3 (Ln 3+ :C12A7; Ln 3+ = Yb 3+ , Tm 3+ and Er 3+ ) synthesized by solid-state reaction method would greatly enhance the scope of its applications ranging from infrared solar cells to field emission display . The scanning electron microscopy (SEM) was used to characterize the morphology of Ln 3+ :C12A7. Under 980 nm excitation, the emission color was tuned from green-yellow to red region through adjusting the concentrations of Ln 3+ ions. The obtained near infrared upconversion (UC) emissions in Ln 3+ :C12A7 was corresponded to “window of optical transparency”. All blue, green and red UC emissions were populated by one-photon process, and the proposed UC mechanisms were studied in Ln 3+ :C12A7.
Single-phase insulating 12CaO∙7Al 2 O 3 (C12A7) powder was synthesized using an optimized hydrothermal method. Pure phase of C12A7 was got at a comparatively lower temperature (c.a. 300 °C) than that has been previously reported. The crystallite size of the synthesized C12A7 powder was 7±2 nm. The surface area values calculated for all the samples at a synthesis temperature range of 250-800 °C for 5 h were in the range of about 19-24 m 2 /g, with pore sizes of 12-20 nm. This low-temperature-based synthetic strategy along with nano porous structures and a high surface area value can facilitate catalyst application.
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