Narrow Band Emission of Pr3+-Activated Oxide-Oxynitride Pervskites Under Near-UV Lights Controlled By Bandgap Engineering

Abstract

In this study, the photoluminescence of Pr3+-acitvated oxide-oxynitride perovskites, CaMxTa1-xO2+xN1-x (M : Zr and Hf) with the range from 0.0 to 1.0 were investigated. This solid-solution system should be expected that the wavelength at maximum exciation intensity is widely adjusted along with bandgap energy between valence and conduction bands by the control of the O/N and Zr (or Hf) /Ta ratios [1]. Thus, the sharp emission peak from Pr3+ in the solid-solution system can be excited by near-UV or blue lights if the width of bandgap energy is adujusted from 2.8 to 3.2 eV. The solid-solution sample were prepred by polymerizable complex method. The obtained precursors were heat-treated under NH3 gas flow at 900-1100oC. XRD patterns indicated that all the samples were of single phase with orthorombic perovskite structure. In the case of CaZrxTa1-xO2+xN1-x, XRD patterns also show the shift of diffraction peaks to low angle region by increasing with Zr4+ concentaration. The absorption was shifted to high-energy sides with increasing Zr4+ concentration. Especially, the bandgap energy were sucessfully adjusted from 2.7 to 3.2 eV while the x was changed from 0.25 to 0.90 by the control of the Zr4+/Ta5+ and O/N ratios. Furthremore, the solid-solution system showed the intersting photoluminous behavior. The single emission peaks were observed at 612 nm when the bandgap enegries were adjusted at around 3.0 eV for the samples with x from 0.55 to 0.70, Such red emission peak can be assigned to the electron transition between 1D2 and 3H4 levels of Pr3+ ions (Fig. 1). In contrast, when the bandgap energy became larger than 3.0 eV, the PL spectra was gradually changed. Several emission peaks were observed in the range from 490 to 750 nm, which can be assinged as the electron transition between 3P0 to 3H4, 3H5 and 3F2 levels [2]. This behavior should be atributed to the width of the bandgap energy of the host compounds. This work was partially supported by JSPS “KAKENHI” (15K06445) and (18K04714). [Reference] [1] Wu et al., Int. J. Hydrogen Energy, 37 (2012) 13704, [2] Nakamura et al., J. Sol-Gel Sci Technol, 61 (2012) 362.