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International audienceThe Dy3+ doped Ga5Ge20Sb10S65 bulk glass provides good emission efficiency in the middle IR with a better brightness than the blackbody sources. Sulfide single index fibers doped with Dy3+ (500-​3000 ppm) were drawn with optical attenuation of about 1-​3 dB​/m, suitable to develop fluorescence sources for chem. anal. by optical absorption in middle IR. They particularly present a broad emission around 4-​5 μm, making them attractive for CO2 detection. Considering the low cost and efficient Dy3+ pumping scheme by means of a com. laser diode, the Dy3+ sulfide fiber reveals potential for developing a CO2 optical sensor. Using the 4.35 μm broad emission of a Dy3+ doped Ga5Ge20Sb10S65 fiber combined with a differential measurement technique, the CO2 gas concn. measurement was carried out fruitfully. For this specific application, the CO2 detection threshold was fixed at about 400 ppm corresponding to atm. concn. and was successfully reached for a cell length of 1.5 cm with a resoln. of about 5​%. The sensitivity of the setup is mainly related to the size of the cell, deliberately reduced to develop a robust and compact system for natural geol. sites

A comparison is presented between Eu implanted and Eu in situ doped GaN thin films showing that two predominant Eu sites are optically active around 620 nm in both types of samples with below and above bandgap excitation. One of these sites, identified as a Ga substitutional site, is common to both types of Eu doped GaN samples despite the difference in the GaN film growth method and in the doping technique. High-resolution photoluminescence (PL) spectra under resonant excitation reveal that in all samples these two host-sensitized sites are in small amount compared to the majority of Eu ions which occupy isolated Ga substitutional sites and thus cannot be excited through the GaN host. The relative concentrations of the two predominant host-sensitized Eu sites are strongly affected by the annealing temperature for Eu implanted samples and by the group III element time opening in the molecular beam epitaxy growth. Red luminescence decay characteristics for the two Eu sites reveal different excitation paths. PL dynamics under above bandgap excitation indicate that Eu ions occupying a Ga substitutional site are either excited directly into the D50 level or into higher excited levels such as D51, while Eu ions sitting in the other site are only directly excited into the D50 level. These differences are discussed in terms of the spectral overlap between the emission band of a nearby bound exciton and the absorption bands of Eu ions. The study of Eu doped GaN quantum dots reveals the existence of only one type of Eu site under above bandgap excitation, with Eu PL dynamics features similar to Eu ions in Ga substitutional sites.

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Spectroscopic properties of Nd:CaF2 crystals with different doping concentrations of Nd3+ and codoping concentrations of Y3+ were investigated. The effect of codoping with Y3+ ions on the absorption and emission spectra, emission lifetimes, quantum efficiency, and emission cross sections of Nd3+ were studied. In particular, codoping with Y3+ ions increases the width of the emission lines over that found with Nd-doped glasses, and allows true CW laser operation around 1.06 μm.

We demonstrate that codoping Nd:CaF 2 single crystals with Y 3 and Lu 3 nonoptically active ions significantly improves their absorption, emission, and fluorescence lifetime properties and their laser performance. The spectral profiles get smoother and wider, wider than that found with standard Nd:glasses; the quantum yields increase; and efficient laser operation is obtained around 1.055 μm.

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