The photoluminescence of Er3+in borosilicate glass is strongly enhanced by the presence of silver. Samples prepared by a combination of erbium ion implantation and Na+↔Ag+ ion exchange show an increase of the Er3+excitation efficiency of up to a factor 70 when excited at 488 nm. Excitation of Er3+ is possible over a broad wavelength range in the near ultraviolet and visible. Our data suggest that absorption of light occurs at a silver ion/atom pair or similar defect, followed by energy transfer to Er3+. We can exclude that silver nanocrystals are part of the dominant excitation mechanism, neither via local field enhancement effects due to their surface plasmon resonance nor via absorption and subsequent energy transfer to Er3+.

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We have used a rate equation propagation model of an Er3+/Yb3+ doped Al2O3 waveguide amplifier with copropagating pump at 980 nm to investigate the dependence of gain on Yb3+ concentration. The model includes excited state absorption and energy transfer upconversion processes within the Er3+ as well as the relevant energy transfer processes between Yb3+ and Er3+. The results of the calculations indicate a close relationship of the parameters gain, launched pump power, waveguide length, and Yb3+ concentration. Codoping with a well-chosen Yb3+ concentration is shown to increase the gain around 1530 nm for all combinations of these parameters. The gain is improved most by Yb3+ codoping at pump powers around the amplifier threshold. At high pump powers the increase in gain of an Er3+/Yb3+ doped waveguide is insignificant compared to that of its Er3+ doped counterpart. Furthermore for each launched pump power, a nonzero Yb3+ concentration can be determined, which maximizes the gain.

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Abstract-The development of a long-term wireless implantable biosensor based on fluorescence intensity measurement poses a number of technical challenges, ranging from biocompatibility to sensor stability over time. One of these challenges is the design of a power efficient and miniaturized electronics, enabling the biosensor to move from bench testing to long term validation, up to its final application in human beings. In this spirit, we present a wireless programmable electronic platform for implantable chronic monitoring of fluorescent-based autonomous biosensors. This system is able to achieve extremely low power operation with bidirectional telemetry, based on the IEEE802.15.4-2003 protocol, thus enabling over three-year battery lifetime and wireless networking of multiple sensors. During the performance of single fluorescent-based sensor measurements, the circuit drives a laser diode, for sensor excitation, and acquires the amplified signals from four different photodetectors. In vitro functionality was preliminarily tested for both glucose and calcium monitoring, simply by changing the analyte-binding protein of the biosensor. Electronics performance was assessed in terms of timing, power consumption, tissue exposure to electromagnetic fields, and in vivo wireless connectivity. The final goal of the presented platform is to be integrated in a complete system for blood glucose level monitoring that may be implanted for at least one year under the skin of diabetic patients. Results reported in this paper may be applied to a wide variety of biosensors based on fluorescence intensity measurement.Index Terms-Biotelemetry, calcium sensing, chronic implants, fluorescence-based biosensor, fluorescence resonant energy transfer (FRET), glucose monitoring, implantable devices.

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Terahertz emission mediated by surface plasmon polaritons in doped semiconductors with surface gratingSurface-plasmon photonic band gaps in dielectric gratings on a flat metal surface