No abstract

No abstract

The development of ultraminiaturized identification tags has applications in fields ranging from advanced biotechnology to security. This paper describes micrometer-sized glass barcodes containing a pattern of different fluorescent materials that are easily identified by using a UV lamp and an optical microscope. A model DNA hybridization assay using these ''microbarcodes'' is described. Rare earth-doped glasses were chosen because of their narrow emission bands, high quantum efficiencies, noninterference with common fluorescent labels, and inertness to most organic and aqueous solvents. These properties and the large number (>1 million) of possible combinations of these microbarcodes make them attractive for use in multiplexed bioassays and general encoding. Encoded bead bioassays are emerging as an attractive alternative to traditional slide-based microarrays because beadbased bioassays offer multiplexing of both probes and samples (the ''analyte''), and they have significantly fewer drawbacks related to mass transport-limited binding of analytes to the immobilized probes. Several approaches have been described for the fabrication of encoded beads: those in which the coding material is randomly distributed in the bead (1, 2) and those in which the coding material is present in a defined pattern on the bead (3). Because different patterns of the same coding materials (e.g., position and thickness of metal stripes on cylindrical particles) result in distinguishable beads (3), a larger number of uniquely encoded beads can be obtained relative to beads with randomly distributed coding materials (e.g., polymer beads infused with mixtures of quantum dots) (2).Current methods for fabricating encoded beads are limited in terms of either the number of possible codes or the compatibility of the beads with bioassays and fluorescence detection. The most widely used method for making encoded beads, infusing polymer microspheres with mixtures of fluorescent dyes in predefined ratios, is not well suited for the fabrication of large (Ͼ10 5 ) numbers of uniquely distinguishable beads. Trau and coworkers have used silica microspheres containing fluorescent dyes for encoding polymer beads by using split-pool methods, and have also described the formation of dye-doped concentric silica layers around core silica particles (4). There are only a limited number of spectrally well-resolved dyes that do not also interfere with commonly used biological labels. Moreover, measurements of intensities and their ratios are inherently difficult, which limits the number of levels at which a dye can be incorporated to give distinguishable beads. Mixtures of quantum dots embedded in polymer microspheres offer significant advantages over conventional fluorescent dyes because they are relatively more photostable and have narrow emission linewidths (2). However, quantum dots are made of toxic materials (e.g., CdS, CdSe, CdTe) (5), and difficulties distinguishing between codes based on different amounts of the same quantum dots are similar to those ...

Low-phonon energy glasses are desirable hosts for rare-earth (RE) ions because they enable emission from RE energy levels that would otherwise be quenched in high-phonon energy glasses. Such emissions are of interest for fiber amplifiers operating at telecommunications wavelength band s of 1.31, 1.46, and 1.55 μm, and for up-conversion lasers and three-dimensional displays.Phonons are optical-frequency molecular vibrations in a material. If the RE energy level of interest lies only a few phonons in energy above the next lower lying level such as the 1G4 level of Pr3+, which is only 3,000 cm −1 above the 3F4, only three Si—O vibrational phonons (1,100 cm−1) are required to bridge the gap as shown in Figure 1. Thus any electrons excited to the 1G4 level via an external pump source will be deexcited to the 3F4 on down to the 3H4 ground state via phonons, and no radiation of usable light will be produced. This is why emission from the 1G4 level of Pr3+ is absent in silicates and why researchers have gone to great lengths to make low-phonon energy glasses.

Primarily to meet the dramatic increase in Internet traffic, a substantial expansion in new fiber-optic networks has been seen in the last few years, increasing the total amount of transmission fiber deployed in the field. However, increased capacity has also been achieved by utilizing more of the available bandwidth present in the currently installed fiber. A key component in facilitating this increase in bandwidth is the erbium-doped fiber amplifier (EDFA), which provides efficient broad-band gain in the 1530–1560-nm telecommunications window. Erbium-doped glasses can be drawn into low-loss fiber, and the width of the gain band can be controlled with glass composition. With appropriate composition and design, EDFAs can simultaneously amplify 32 or more wavelengths, providing a 32-fold increase in data capacity over single-channel systems. These devices can boost signal strength by a factor of 1000, with high reliability and low noise at data rates exceeding 1 Tbit/s. In this article, we review some of the properties that are key to the success of EDFAs and discuss the potential for other rare-earth-doped glass-fiber combinations that may find possible applications in future telecommunications networks.Fiber optics have revolutionized the telecommunications industry, providing more information capacity and greater distances between signal boosters than copper wire and coaxial cable. The attenuation in coaxial systems increases exponentially with signal frequency, making high-speed transmission over long distances impractical. The best copper systems have a bandwidth of about 10 Mbit/s and are limited to lengths of less than 200 m at high data rates. In contrast, the attenuation of SiO2 optical fibers is low and independent of signal frequency, thus optical fiber can easily support 100 Gbit/s (10,000 times the capacity of copper) over 80 km and is currently only limited by the speed of the transmission and receiving electronics, with capacities in excess of 50 Tbit/s theoretically possible.1 For links in excess of 80 km, signal amplification is necessary to prevent total loss of the signal. In the 1980s, amplification was done with electronic devices called repeaters that detected the light, converted it to an electronic signal, amplified, retimed, and then retransmitted it as an optical pulse.The field of optical telecommunications has itself undergone a revolution. In the late 1980s, the invention of the all-optical amplifier allowed for simultaneous amplification of multiple channels in a single optical fiber each at a different wavelength or color of light. SiO2 fibers have a minimum in attenuation in the infrared (IR) portion of the optical spectrum near 1550 nm, as shown in Figure 1. The EDFA fortuitously provides high gain and low noise in the 1530-1560-nm spectral window. This technology now enables simultaneous amplification of 32 channels in a single fiber without the need for optical-to-electronic conversion. Thus single-fiber capacities of 320 Gbit/s are currently being deployed today. To perform this electronically, each channel would have to be separated (demultiplexed), amplified by its own costly repeater, and then recombined (multiplexed) in the fiber. Researchers are now perfecting 100-channel EDFAs in the lab.

NMR determinations of fluorine environments in transparent oxyfluoride glass-ceramics were made to learn about the crystallization of LaF 3 , as well as to ascertain the structural role of fluorine in the surrounding glassy matrix. The fraction of fluorine in LaF 3 was measured as a function of heat treatments, demonstrating significant differences between glasses modified with barium and those containing sodium. The results of these measurements showed that not all of the fluorine formed LaF 3 in these glass-ceramics, with resolution of additional fluoride sites at ؊135 and ؊185 ppm, due primarily to Si-F and Al-F bonding, respectively. Not only is the evidence of Si-F bonding unexpected, given the presence of aluminum, but the amount of Si-F bonding is sensitive to the type of modifier in the glass. Samples containing barium oxide as the modifier showed a higher fraction of Si-F bonding than those modified with sodium oxide.

Structural and spectroscopic properties of rare-earth ( Nd 3+ , Er 3+ , and Yb 3+ ) doped transparent lead lanthanum zirconate titanate ceramics This work studies the spectroscopic behavior of Eu 3ϩ -doped and Yb 3ϩ /Er 3ϩ -codoped single crystals of orthorhombic LaBO 3 and rhombohedral GdBO 3 . Emissions from Er 3ϩ at ϳ1535 nm are shown to exhibit multiple narrow linewidth emissions. Luminescence from the 5 D 0 → 7 F 1 , 7 F 2 transitions of Eu 3ϩ is found to depend on the choice of LaBO 3 or GdBO 3 as a parent phase in a well-defined manner. Phonon sideband spectroscopy of the Eu 3ϩ 5 D 2 excitation, corroborated using Raman spectroscopy, indicates that the highest energy phonon is less than 1400 cm Ϫ1 for the LaBO 3 and less than 1010 cm Ϫ1 for the GdBO 3 . Further, absorption spectrum to 190 nm is provided for the GdBO 3 clearly showing the 6 I manifold, and the rarely seen 6 D levels. Excitation of the 6 D 7/2 state at 250 nm in GdBO 3 is shown to yield a strong ultraviolet emission centered at 314 nm. This work marks the lanthanide borates as candidate single crystals for active and nonlinear materials for UV, visible, and telecommunication band applications.

The low-temperature homogeneous broadening of the electronic transitions of Eu 3ϩ and Pr 3ϩ rare-earth impurity ions in Y 2 O 3 and LaF 3 nanocrystals embedded into amorphous materials ͑polymer and oxyfluoride glass ceramics͒ was studied with hole-burning and fluorescence line narrowing techniques. It is shown that the homogeneous linewidth is determined by the interaction of the impurity ions contained in the nanocrystals with the two-level systems ͑TLS's͒ of the surrounding glass matrix. A comparison of the experiments with a calculation provides direct evidence for the long-range nature of the interaction with the TLS's. DOI: 10.1103/PhysRevB.64.100201 PACS number͑s͒: 78.67.Ϫn, 78.67.Bf It is well known that when rare-earth ͑RE͒ ions are doped into glasses, their dynamics are governed by interactions with the two-level systems ͑TLS's͒ of the glass. Experiments in many systems provide evidence that at low temperatures the homogeneous linewidths, ␥ h , in these systems obey a power law in temperature, ␥ h ϳT ␣ with 1Ͻ␣Ͻ2. Theoretical calculations show that this behavior is predicted for interactions with the TLS's of the glass. [1][2][3][4][5] With the recent availability of nanocrystals containing RE ions, it is of great interest to determine whether RE ions separated from the glassy TLS's by the crystalline nanoparticle in which they are contained also exhibit interactions with TLS's when the nanoparticles are embedded in an amorphous matrix such as a glass. This can provide an independent test of the TLS model and can determine the length scale of the interactions.It has been recently determined that materials consisting of insulating nanocrystals doped with RE ions embedded into amorphous ͑glassy͒ matrices possess nearly identical spectra to those of RE ions in single crystals of the same crystalline composition and structure.6 This is not unexpected, as the optical spectra of RE ions are determined by the short-range local environment of the RE site, which ͑with the exception of the ions at the nanocrystal-glass interface͒ remains unperturbed in crystallites of a few nanometers size. The sharp line spectra allow one to spectrally isolate ions in the nanoparticles from those in the amorphous matrix. Here we apply the technique of spectral hole burning to examine their dynamical properties. This work is motivated, in part, by the interest in these materials for applications such as hole-burning memories 7 and optical processors. 8,9The mechanisms responsible for changes in the dynamical properties of the excited states of RE ions in insulating nanocrystals embedded in amorphous matrix, compared to single crystals, can be grouped into two categories: ͑i͒ those connected with size restriction effects and ͑ii͒ those caused by the interaction of RE ions with the amorphous environment surrounding the crystallites. The effects of the first kind are due mainly to the modification of the phonon spectrum of the nanocrystals at low frequencies due to their sizerestricted nature as reported for ''free-standing'' na...