We prepared Eu3+- and Yb3+-doped ZrO2 nanoparticles at two different annealing temperatures of 500 and 1300 °C. The structural analysis of the samples was performed using X-ray diffraction. A detailed analysis of the downconversion and upconversion spectra of the samples has been carried out. Emission peaks (green and red) of Eu3+ ions, as well as host emission (blue light), are observed. The emission intensity increases with the excitation slit width, following the Beer–Lambert Law. Further, many peaks of Eu3+ ions in the range of 300 to 800 nm have been observed through an upconversion process upon excitation with a 980 nm laser source. With an increase of the slit width (W) in the emission monochromator, the luminescence intensity (I) increases, following log (I) ∝ log (W). This is a nonlinear phenomenon. The emission peaks observed in the upconverted spectrum are assigned according to the literature. The cooperative energy transfer from 2Yb3+ ions to Eu3+ ions has been explained. The maximum number of Eu3+ emission peaks (double to singlet) has been observed by varying the emission slit widths. Blue and white lights are obtained from the samples through downconversion and upconversion studies, respectively.
Srivastava et al. (Tue,) studied this question.