Basudeb Karmakar

Nanosilver enhanced upconversion fluorescence of erbium ions in Er3+: Ag-antimony glass nanocomposites

Er3+:Ag-antimony glass nanocomposites are synthesized in a new reducing glass (dielectric) matrix K2O–B2O3–Sb2O3 by a single-step melt-quench technique involving selective thermochemical reduction. The UV-vis-near-infrared absorption spectra show typical surface plasmon resonance (SPR) band of Ag0 nanoparticles (NPs) in addition to the distinctive absorption peaks of Er3+ ion. X-ray diffraction and selected area electron diffraction results indicate formation of Ag0 NPs along the (200) plane direction. The transmission electron microscopic image reveals the formation of spherical, fractal, and rod-shaped Ag0 NPs having maximum size ∼31 nm. The rod-shaped Ag0 NPs have aspect ratio ∼2.4. The field emission scanning electron microscopic image shows development of three dimensional cornlike microstructures. Photoluminescent upconversion under excitation at 798 nm exhibit two prominent emission bands of Er3+ ions centered at 536 (green) and 645 (red) nm due to S43/2→I415/2 and F49/2→I415/2 transitions, respect...

Enhancement of Er 3+ upconverted luminescence in Er 3+ : Au-antimony glass dichroic nanocomposites containing hexagonal Au nanoparticles

Dichroic Er3+:Au-antimony glass nanocomposites are synthesized in a new reducing glass (dielectric) matrix (mol%) K2O-B2O3-Sb2O3 (KBS) by a single-step melt-quench technique involving selective thermochemical reduction principle. Transmission electron microscopic images reveal hexagonal Auo nanoparticles having major axes about 9-23 nm. Dichroic behavior arises due to hexagonal Auo nanoparticles of aspect ratio 1.2-1.3. Auo nanoparticles of concentration of 0.03 wt%(4.1×1018 atoms/cm3) drastically enhances the intensity (2-5 folds) of both 536 (S3/24-->I15/24, green) and 645 (F9/24-->I15/24, red) nm emission bands of Er3+. Local field enhancement induced by Auo surface plasmon resonance (SPR) and energy transfer from fluorescent Auo-->Er3+ ions are found to be responsible for enhancement while, at very high Au concentration, energy transfer from Er3+-->Auo and optical reabsorption due to Auo SPR result in quenching.

Optical properties of Eu3+-doped antimony-oxide-based low phonon disordered matrices

A new series of monolithic Eu(2)O(3)-doped high antimony oxide (40-80 mol%) content disordered matrices (glasses) of low phonon energy (about 600 cm(-1)) in the K(2)O-B(2)O(3)-Sb(2)O(3) (KBS) system was prepared by the melt-quench technique. Infrared reflection spectroscopy was used to establish the low phonon energy of the glasses. Amorphicity and devitrification of the glasses were confirmed by x-ray diffraction analysis. UV-vis absorption spectra of Eu(3+) have been measured and the band positions have been justified with quantitative calculation of the nephelauxetic parameter and covalent bonding characteristics of the host. These Eu(2)O(3)-doped glasses upon excitation at 393 nm radiation exhibit six emission bands in the range 500-750 nm due to their low phonon energy. Of these, the magnetic dipole (5)D(0) --> (7)F(1) transition shows small Stark splitting while the electric dipole (5)D(0) --> (7)D(2) transition undergoes remarkable Stark splitting into two components. They have been explained by the crystal field effect. The Judd-Ofelt parameters, Ω(t = 2,4,6), were also evaluated and the change of Ω(t) with the glass composition was correlated with the asymmetric effect at Eu(3+) ion sites and the fundamental properties like covalent character and optical basicity. We are the first to report the spectroscopic properties of the Eu(3+) ion in KBS low phonon antimony glasses.

Optical and dielectric properties of isothermally crystallized nano-KNbO3 in Er3+-doped K2O–Nb2O5–SiO2 glasses

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.

Enhanced frequency upconversion of Sm3+ ions by elliptical Au nanoparticles in dichroic Sm3+: Au-antimony glass nanocomposites

Dichroic Sm(3+): Au-antimony glass nanocomposites are synthesized in a new reducing glass (dielectric) matrix (mol%) K(2)O-B(2)O(3)-Sb(2)O(3) (KBS) by a single-step melt-quench technique involving selective thermochemical reduction. X-ray diffraction (XRD) and selected area electron diffraction (SAED) results indicate that Au(0) nanoparticles are grown along the (200) plane direction. The transmission electron microscopic (TEM) image reveals the elliptical Au(0) nanoparticles having major axis range 12-17 nm. Dichroic behavior is due to elliptical shape of Au(0) nanoparticles of aspect ratio approximately 1.2. Au(0) NPs of concentration of 0.03 wt% (4.1 x 10(18)atoms/cm(3)) drastically enhances the intensity ( approximately 7-folds) of electric dipole (4)G(5/2)-->(6)H(9/2) red transition (636 nm) of Sm(3+) ions and then attenuates with further increase in Au(0) concentration. The magnetic dipole (4)G(5/2)-->(6)H(5/2) green (566 nm) and (4)G(5/2)-->(6)H(7/2) orange (602 nm) transitions remain almost unaffected by presence of nano Au(0). Local field enhancement (LFE) induced by Au(0) SPR and energy transfer (ET) from fluorescent Au(0)-->Sm(3+) ions are found to be responsible for the enhancement while reverse ET from Sm(3+)-->Au(0) and optical re-absorption due to Au(0) SPR for attenuation.