Eu3+ fluorescence spectroscopy is used to investigate the clustering of rare-earth ions and the effectiveness of aluminum codoping in dispersing and isolating rare-earth ions in solgel silica monoliths. Fluorescence line-narrowing (FLN) studies are demonstrated as a useful tool in identifying clustered and isolated Eu3+. Clustered Eu3+ is identified by the lack of a line-narrowing effect, which is attributed to energy transfer between adjacent Eu3+ ions.Clustering is shown to be significant, even in transparent samples with Eu3+ concentrations as low as 0.5 wt % Eu3+. Addition of Al3+ as a codopant has a profound impact on the bonding and structure of Eu3+ in silica. Significant fluorescence line narrowing is observed, which suggests that Al3+ codoping is effective in dispersing and isolating Eu3+ ions in the silica matrix. Fluorescence decay studies provide evidence of increased Eu3+ hydroxylation in the Al3+-containing samples.

Fluorescence line-narrowing spectroscopy is used to characterize the effect of metal cation codopants (Sr2+, La3+, Gd3+, Y3+, Lu3+, Sc3+, and Ga3+) on the state of aggregation of Eu3+ in sol−gel silica. Significant Eu3+ clustering occurs in samples doped only with Eu3+. The addition of codopants inhibits the clustering of Eu3+ and promotes better dispersion of Eu3+ in the glasses. The extent of the inhibition of clustering increases with field strength of the codopant and levels off at high field strength. The inhibition of clustering is correlated with the generation of strong crystal field bonding sites for Eu3+ in the presence of codopants. Characteristics of these sites include the presence of Eu−O−M (M = codopant) linkages and stronger interactions with the network-forming regions of the glass. Supporting luminescence decay and Raman spectroscopy measurements are also presented.

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We report on the effect of high pressure on the room-temperature emission spectra and lifetimes of Cr +:GSGG (Gd3SC2Ga30») and Cr:GGG (Gd3Ga50»). In both systems we observed a dramatic change of the overall emission band shape upon increasing pressure, from a nearly structureless broadband ( T2~A 2 ) to a highly structured narrow band ( E~A 2 )~From the peak energy of the broadband emission, we estimated the pressure-induced blueshift of the T2~A2 transition to be 10 (+2) cm '/kbar. High-resolution measurements in the R-line region ( -700 nm) revealed that the E -+ A2 transition hardly shifts at low pressures ( &40 kbar), whereas at higher pressures ()60 kbar) a nearly linear redshift of 0.65 (+0.05) cm /kbar is observed. Besides pressure-induced spectral changes, an enormous increase in the emission lifetime with increasing pressure was found for both systems. In the case of Cr +:GSGG, the lifetime changed from 110 ps at ambient pressure to 4.4 ms at 125 kbar. For Cr'+:GGG, the lifetime increased from 168 ps to 7.3 ms for the same pressure range. The pressureinduced spectral and lifetime changes are described by a single configurational coordinate model that considers the effect of pressure on the thermal and spin-orbit coupling of the E and T2 states. A previously reported pressure-induced R-line-shift reversal in Cr +:GSGG and the effect of high pressure on the lifetime in Cr +: YAG are also discussed within the same framework.

We report a spectroscopic study on the photoluminescence (PL) of erbium implanted into porous silicon (Er:PSi). Two different porous Si samples were implanted with a dose of 1015 Er/cm2 at 380 keV and annealed at 650 °C for 30 min under identical conditions. Both samples exhibited Er3+ luminescence at 1.54 μm, which was quenched by less than a factor of two between 15 K and room temperature. Visible PL studies of Er implanted and annealed porous Si samples showed broad spectra which peaked at ∼700 nm for sample A and peaked at ∼660 nm for sample B. Sample A showed a four times stronger Er3+ luminescence than that observed from sample B. In contrast, temperature quenching of the Er3+ luminescence was found to be similar or slightly weaker from sample B than from sample A. The spectroscopic data will be discussed in terms of the excitation mechanisms of Er3+ in porous Si nanostructures.

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