Cooperative luminescence from low temperature synthesized α-Al2O3: Yb3+ phosphor by using solution combustion

Ytterbium (Yb3+) doped aluminium oxide (Al2O3) powder phosphor was successfully synthesized by solution combustion method. The structure, vibrational bending modes, particle morphology, chemical composition, and photoluminescent properties were analyzed using X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS) and photo luminescent (PL) spectroscopy respectively. The XRD patterns confirmed that Al2O3 crystallized in its stable polymorphic hexagonal alpha-Al2O3 phase with space group R3c. The average crystallite size estimated from Debye-Scherrer equation was 29 nm. The FTIR confirmed the Al-O vibrations associated with a-Al2O3 and the Yb-O vibrations. The SEM data showed that the powders were made up of particles with different shapes but well defined boundaries. Furthermore, the SEM images show that the Yb3+ ions resided on the grain boundaries. When the powders were excited using a 325 nm He-Cd laser, the emission was observed in the near infrared (NIR) at 975 nm due to the F-2(5/2) -> F-2(7/2) transition of Yb3+. However, the bluish green emission with a maxima at similar to 480 nm was observed as a result of cooperative luminescence of Yb3+ when the powders were excited in the NIR with an excitation wavelength of 980 nm. Cooperative energy transfer (CET) mechanism producing NIR emission for the 325 nm laser excited Al2O3:Yb3+ powders is presented and discussed.