title: Optical and dielectric properties of isothermally crystallized nano-KNbO3 in Er3+-doped K2O-Nb2O5-SiO2 glasses.
abstract: Precursor glass of composition 25K(2)O-25Nb(2)O(5)-50SiO(2) (mol%) doped with Er(2)O(3) (0.5 wt% in excess) was isothermally crystallized at 800 degrees 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 (2)H(11/2), (4)S(3/2)-->(4)I(15/2) upon excitation at 377 nm ((4)I(15/2)-->(4)G(11/2)) absorption band of Er(3+) ions. The near infrared (NIR) emission transition (4)I(13/2)-->(4)I(15/2) is detected around 1550 nm on excitation at 980 nm ((4)I(15/2)-->(4)I(11/2)) of absorption bands of Er(3+) ions. It is observed that photoluminescent intensity at 526 nm ((2)H(11/2)-->(4)I(15/2)), 550 nm ((4)S(3/2)-->(4)I(15/2)) and 1550 nm ((4)I(13/2)-->(4)I(15/2)) initially decrease and then gradually increase with increase in heat-treatment time. The measured lifetime (tau(f)) of the (4)I(13/2)-->(4)I(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.
authors.affiliation: Glass Division, Central Glass and Ceramic Research Institute (Council of Scientific and Industrial Research), Kolkata, India.
authors.forename: Reenamoni Saikia
authors.initials: RS
authors.lastname: Chaliha
authors.forename: K
authors.initials: K
authors.lastname: Annapurna
authors.forename: Anal
authors.initials: A
authors.lastname: Tarafder
authors.forename: V S
authors.initials: VS
authors.lastname: Tiwari
authors.forename: P K
authors.initials: PK
authors.lastname: Gupta
authors.forename: Basudeb
authors.initials: B
authors.lastname: Karmakar
mesh_terms: D003460:Crystallization; D004563:Electrochemistry; D004871:Erbium / Q000737:chemistry*; D005898:Glass / Q000737:chemistry*; D046529:Microscopy, Electron, Transmission; D053758:Nanoparticles / Q000737:chemistry*; D009556:Niobium / Q000737:chemistry*; D010087:Oxides / Q000737:chemistry*; D011188:Potassium / Q000737:chemistry*; D017680:Potassium Compounds / Q000737:chemistry*; D012822:Silicon Dioxide / Q000737:chemistry*; D017550:Spectroscopy, Fourier Transform Infrared; D014961:X-Ray Diffraction
chemical_list: D010087:Oxides; D017680:Potassium Compounds; D009556:Niobium; C477466:potassium niobate; C068440:potassium oxide; D012822:Silicon Dioxide; D004871:Erbium; C073337:niobium pentoxide; D011188:Potassium