Optical and dielectric properties of isothermally crystallized nano-KNbO 3 in Er 3+-doped K 2O–Nb 2O 5–SiO 2 glasses

Abstract

Precursor glass of composition 25K 2O–25Nb 2O 5–50SiO 2 (mol%) doped with Er 2O 3 (0.5 wt% in excess) was isothermally crystallized at 800 °C for 0–100 h to obtain transparent KNbO 3 nanostructured glass–ceramics. XRD, FESEM, TEM, FTIRRS, dielectric constant, refractive index, absorption and fluorescence measurements were carried out to analyze the morphology, dielectric, structure and optical properties of the glass–ceramics. The crystallite size of KNbO 3 estimated from XRD and TEM is found to vary in the range 7–23 nm. A steep rise in the dielectric constant of glass–ceramics with heat-treatment time reveals the formation of ferroelectric nanocrystalline KNbO 3 phase. The measured visible photoluminescence spectra have exhibited green emission transitions of 2H 11/2, 4S 3/2 → 4I 15/2 upon excitation at 377 nm ( 4I 15/2 → 4G 11/2) absorption band of Er 3+ ions. The near infrared (NIR) emission transition 4I 13/2 → 4I 15/2 is detected around 1550 nm on excitation at 980 nm ( 4I 15/2 → 4I 11/2) of absorption bands of Er 3+ ions. It is observed that photoluminescent intensity at 526 nm ( 2H 11/2 → 4I 15/2), 550 nm ( 4S 3/2 → 4I 15/2) and 1550 nm ( 4I 13/2 → 4I 15/2) initially decrease and then gradually increase with increase in heat-treatment time. The measured lifetime ( τ f) of the 4I 13/2 → 4I 15/2 transition also possesses a similar trend. The measured absorption and fluorescence spectra reveal that the Er 3+ ions gradually enter into the KNbO 3 nanocrystals.