Control of the Emission and Excitation Energies in Pr3+-Activated Perovskite Oxide–Oxynitrides by Bandgap Engineering

In this paper, we propose a new concept for the material design for near-ultraviolet (UV)-excited narrow-band phosphors with f–f emissions by bandgap engineering. The perovskite oxide–oxynitride solid solutions, namely, CaTa1–xZrxO2+xN1–x, were used as host materials to demonstrate our design principle. Photoluminescence (PL) excitation and emission control were systematically performed on Pr3+-activated CaTa1–xZrxO2+xN1–x, where x is in the range of 0.0–1.0. Tuning the PL excitation wavelength was archived over a large wavelength range by tailoring the bandgap of CaTa1–xZrxO2+xN1–x with different Ta/Zr and N/O ratios. Notably, an intense red emission from Pr3+ was observed at 614 nm under the near-UV irradiation of 375 nm when the bandgap of the host material CaTa1–xZrxO2+xN1–x (x = 0.75) was approximately 3.0 eV. Such a red emission peak was assigned to the electron transition between the 1D2 and 3H4 levels of the Pr3+ ions. In contrast, when the bandgap was above 3.0 eV, the PL emission spectra were systematically varied with the bandgap of the host materials. Some emission peaks from the electron transition between 3P0 and 3H4, 3H5, and 3F2 levels were observed in the samples with x = 0.90 and x = 0.95. Our results indicate that the PL properties of the phosphors with f–f emission are systematically controlled based on the bandgap engineering for the host materials.