Structure, dielectric and optical properties of transparent Nd³⁺: KNbO₃ nanocrystalline glass-ceramics

Abstract

Here, glass in the composition of 25K₂O-25Nb₂O₅-50SiO₂ (mol%) doped with Nd₂O₃ (0.5 wt.% in excess) was isothermally crystallized at 800 °C for 1-100 h. Their structures, dielectric and optical properties were analyzed with the progress of nanocrystallization of Nd³⁺: KNbO₃ by XRD, FESEM, TEM, FTIRRS, DC, optical absorption and fluorescence measurements. Crystallization of KNbO₃ is confirmed from XRD and the appearance of 749 cm^-1 band in the FTIRRS spectra. The crystallite size estimated from XRD and TEM is found to vary in the range 7-11 nm. The formation of ferroelectric nano-crystalline KNbO₃ phase is also attributed by a steep rise in the dielectric constant (ε ) of glass-ceramics with heat-treatment time. The measured photoluminescence spectra have exhibited emission transitions of ⁴F_3/2 → ⁴I_J (J = 9/2, 11/2 and 13/2) from Nd³⁺ ions upon excitation at 817 nm. It is observed that the photoluminescent intensity and excited state lifetime of Nd³⁺ ions initially decrease and then gradually increase with increase in heat-treatment time. The absorption spectra and fluorescence measurements disclose that the Nd³⁺ ions gradually enter into the KNbO₃ nanocrystals.