Abani Biswas

Blue cooperative upconversion in Yb3+-doped multicomponent sol-gel-processed silica glass for three-dimensional display

We propose using blue cooperative upconversion of ytterbium (Yb3+) ions produced by a one-color one-beam pumping scheme for a three-dimensional fluorescence display. The results are presented using a diode laser as a pump source emitting at 973 nm, and the sample used was a multicomponent sol-gel-processed silica glass (1 mol. % of Yb3+). The maximum absolute blue power emitted was ∼1 μW for an excitation power of ∼900 mW.

Infrared-to-visible Eu3+ energy upconversion due to cooperative energy transfer from an Yb3+ ion pair in a sol–gel processed multi-component silica glass

Energy upconversion of Eu3+ is demonstrated in a sol–gel processed silica glass co-doped with Yb3+ ions. Yellow–orange emission is observed originating from the Eu3+ ions due to nonresonant cooperative energy transfer from pairs of excited Yb3+ ions when a diode laser emitting at a wavelength of 973 nm is used as an excitation source. The Yb3+–Eu3+ energy transfer rate is estimated as ∼280 s−1 based on an analysis of the Yb3+ infrared luminescence decay time.

Highly efficient infrared-to-visible energy upconversion in Er(3+):Y(2)O(3).

Very intense green and red emission was observed at room temperature from the (4)S(3/2) and (4)F(9/2) levels of Er(3+):Y(2)O(3). A cw diode laser at 975 nm was used as a pump for resonant sequential excitation of the (4)I(11/2) and (4)F(7/2) levels. The fluorescence was easily visible to the naked eye, even with 27 mW of excitation power. It was found that at 850 mW of cw excitation power the total luminance was 39,000 cd/m(2). This corresponds to ~100 muW of green emission and 270 muW of red emission.

Er3+-doped multicomponent sol-gel-processed silica glass for optical signal amplification at 1.5 μm

We have developed a multicomponent K–Er codoped silica-based sol-gel glass that presents high luminescence quantum yield (∼100 times larger than that of an Er-doped silica sol-gel glass) and long emission lifetime at 1.54 μm (17 ms). The glass was heat treated to melting temperature with the optical properties of the system remaining practically unchanged. The IR absorption data shows that the hydroxyl content of this multicomponent glass is drastically reduced to a few tens of parts per million by using optimized compositions. The maximum gain coefficient expected for this glass is ∼4.5 dB/cm at 1.5 μm.

Spontaneous reduction of Eu3+ ion in Al co-doped sol-gel silica matrix during densification

Abstract Eu and Eu-Al co-doped silica glasses have been prepared by impregnating the pores of a base catalysed tetraethylorthosilicate (TEOS) gel with the nitrate salt of Eu and Al and subsequent densification around 1125 to 1150°C. Absorption, emission and excitation spectra of these glasses indicate that Eu 3+ ions are spontaneously reduced to Eu 2+ in the presence of Al 3+ during sintering of the glasses above 1000°C.

Optical properties of Europium doped gels during densification

Abstract Base catalyzed porous silica sol–gel monoliths fired at 1000°C were used to prepare Eu and Eu–Al co-doped glasses by post doping and subsequent densification around 1125–1150°C in air. Both Eu3+ and Eu2+ ions were found to coexist in densified Al co-doped glasses. The absorption, emission and excitation spectra of the Eu-doped glasses are significantly dependent on the alumina content. The densification temperature of the doped gel also played a major role in the reduction process. The UV excitation efficiency for the 5 D 0 → 7 F 2 transition of Eu3+ ions (614 nm) was increased in the presence of Eu2+ ions due to energy transfer from Eu2+ to Eu3+ ions.

Quasi-Resonant Nonlinear Absorption for Optical Power Limiting: solgel-Processed Er(3+)-Doped Multicomponent Silica Glass.

We demonstrate optical power limiting by what we believe to be a new mechanism of nonlinear absorption, which involves a quasi-resonant ground-state absorption that is either phonon assisted or assisted by the presence of defect sites (tail absorption). Such a mechanism provides high transmittance at low intensity yet optical limiting under cw conditions. The sample used was a novel solgel-processed Er(3+)-doped multicomponent silica glass. In this system the nonlinear absorption process is achieved because the resonant excited-state ((4)I(13/2) ? (4)S(3/2)) absorption cross section is larger than the quasi-resonant ground-state ((4)I(15/2) ? (4)I(9/2)) absorption cross section.

Two-Photon Processes: Dynamics and Applications

Recent advances in producing highly efficient two-photon up-converters have opened up a great number of potential applications. This paper describes our effort in the development of highly efficient organics with direct two-photon absorption and inorganics with sequential as well as cooperative two-photon processes. An important part of our program is characterization of the two-photon excitation dynamics using femtosecond time-resolved studies for a direct two-photon absorption process in organics. A major effort of our program is developing two-photon technology. In this paper two specific applications are reviewed: (i) Optical power limiting and (ii) Optical tracking of chemotherapy.

Nanophotonics: Nanoscale Optical Science and Technology

Nanophotonics defined as nanoscale optical science and technology is a new frontier, which includes nanoscale confinement of radiation, nanoscale confinement of matter, and nanoscale photophysical or photochemical transformation. Selected examples of our research work in each of these areas are presented here. Nonlinear optical interactions involving nanoscale confinement of radiation is both theoretically and experimentally studied using a near-field geometry. The effort in nanoscale confinement of optical domains is focused to control excitation dynamics and energy transfer as well as to produce photon localization using nanostructured rare-earth doped glasses and novel inorganic-organic photorefractive nanocomposites. Spatially localized photochemistry using a near-field two-photon excitation is being developed for nanofabrication and nanoscale memory.

Nanoscale Chemistry and Processing of Multifunctional Composites for Nanophotonics and Biophotonics

Abstract Multifunctional nanostructured materials and composites are of considerable interest for photonics, optoelectronics and biophotonics. This paper will focus on three topics. In the first part of the paper, we will focus on silica encapsulated multifunctional nanoparticles. These particles show enhanced optical properties as well as photo, chemical and thermal stability. In the second part of the paper, we investigate the Er3+ sol-gel multicomponent silica glass prepared with nanostructure control for 1.55 μm amplification. These glasses demonstrate the longest reported lifetime in sol-gel glasses to date, which we attribute to the reduction of the hydroxyl content in the glass. The third part of the paper discusses our work on photonic crystals.