Abstract
Herein, we report the luminescence properties of (1%) Ho and (1%) Ho, (20%) Yb–CeO2 nanoparticles, investigated by time-resolved luminescence spectroscopy at 300 and 80K temperatures. The emission was measured over a broad detection range, from visible (450nm) up to infrared (1500nm) with excitation ranging from 210 to 1000nm. The structural properties were characterized by X-ray diffraction, Raman, Diffuse Reflectance Optical and Diffuse Reflectance Fourier Transform Infrared spectroscopies. The up-conversion emission of Ho–CeO2 and Ho, Yb–CeO2 using excitation wavelengths of 646.6, 759, 918and 971nm, respectively, were described in terms of time-gated up-conversion emission and excitation spectra, as well as up-conversion emission decays. Under short gate/ short delay conditions, the contribution of the 5F3 and 5F5 energy levels to the red emission of Ho at 630–680nm could be separated. The role of CeO2 charge transfer band as a selective antenna sensitizer as well as back transfer of excitation from Ho to Yb was also discussed. The mechanisms involved in the up-conversion emission of Ho and Ho, Yb–CeO2 were interpreted as ground state absorption followed by excited state absorption and energy transfer, respectively. For Ho, Yb–CeO2, a tunable red to green up-conversion emission ratio from 0.5 to 3.6 was also observed by increasing the power density of ~4 to 48W/cm2 of a cw laser diode at 980nm.
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