Following the demonstration of room-temperature luminescence, Er 2 O 3 has been explored as a high-gain medium for ultra-compact waveguide amplifiers. With sputtered and annealed films, we measure three radiative lifetimes (7 ms, 0.8 ms, and 0.5 ms) and upconversion coefficients at 4.2 K. We have correlated these measurements with three crystalline phases: the thermodynamically stable bcc phase and the metastable fcc and hcp phases. The 7-ms lifetime is correlated with the fcc phase, implying the metastable crystal state has a profound influence on inhibiting upconversion interaction between neighbor Er atoms. Measurements indicate optical gain Ͼ3 dB/cm is possible.
Nanocrystalline Ge in SiO 2 was synthesized by the reduction of Si 0.75 Ge 0.25 O 2 with H 2 , at various annealing temperatures ͑ranging from 700 to 900°C͒, with various H 2 partial pressures (100% N 2 , 6% H 2 :94% N 2 , and 100% H 2 ), and for a range of times. Cross-sectional transmission electron microscopy ͑XTEM͒ reveals a strong dependence of nanocrystal distribution and structure on annealing temperature and H 2 partial pressure. The oxide/semiconductor interface served as a seed layer for the growth of large Ge crystallites, whereas nanocrystals formed in the bulk of the oxide for high H 2 partial pressures or low temperatures. The mechanisms involved in nanocrystal formation are discussed in the context of XTEM and Raman spectroscopy results. Select nanocrystalline Ge samples were characterized optically with infrared photoluminescence ͑PL͒ measurements at 4 K, using a 488 nm Ar laser excitation. Nanocrystalline Ge samples with small nanocrystals (Ͻ15 nm) exhibited a broad infrared PL background ranging from about 1.0-1.7 m. The broad background is attributed to quantum confinement in the Ge nanocrystals, consistent with a wide distribution of nanocrystal sizes and hence a broad range of confinement energies.
A set-up for varying the temperature (5-90 degrees C) of planar optical waveguides useful in sensing applications is described. The principle is to control the temperature of the cover medium (in this case water). The propagation constants of guided modes are measured via a grating coupler. Only that part of the waveguide in the immediate vicinity of the incoming external light beam is heated or cooled. The temperature coefficients of the thickness and refractive index of the waveguide material can be described by simple polynomial expressions.
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