Sensitizing effect of Yb 3+ on near-infrared fluorescence emission of Cr 4+ -doped calcium aluminate glasses
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Sensitizing effect of Yb3+ on near-infrared fluorescence emission of Cr4+-doped calcium aluminate glasses Yong Gyu Choia) and Kyong Hon Kim Telecommunication Basic Research Laboratory, Electronics and Telecommunications Research Institute (ETRI), Yusong P.O. Box 106, Taejon 305-600, Korea
Yong Seop Han and Jong Heo Photonic Glasses Laboratory, Department of Materials Science and Engineering, Pohang University of Science and Technology (POSTECH), San 31, Hyoja-dong, Nam-gu, Pohang, Kyungbuk 790-784, Korea (Received 6 June 1999; accepted 4 November 1999)
We have demonstrated that an efficient energy transfer takes place from Yb3+ to Cr4+ in calcium aluminate glasses. Yb3+ improves excitation efficiency at around 980 nm, enhancing emission intensity of Cr4+ fluorescence at 1.2–1.6 m. Nonradiative energy transfer via electric dipole–dipole interaction between ytterbium and chromium ions was found to be dominant over radiative Yb3+ → Cr4+ energy transfer. A diffusionlimited energy transfer mechanism well explains the decay behavior of Yb3+/Cr4+codoped glasses. This codoping scheme may be applicable to other Cr4+-containing crystals and glasses.
Conventional oxide glasses exhibit strong adsorption in the 3.5–5 m region, while infrared (IR) transmission cutoff of calcium aluminate glasses is around 6 m wavelength, which is mainly attributed to low vibrational energy (∼700 cm−1) of these glasses compared to that (typically higher than 900 cm−1) of the conventional oxide glasses.1 Calcium aluminate glasses have been estimated to show the sum of scattering losses of approximately 0.04 dB/km at 1.55 m.2 In addition, these glasses exhibit a mechanical strength comparable to that of some silicate glasses.3 On the other hand, binary CaO– Al2O3 glasses have a narrow glass-forming region and a pronounced tendency toward devitrification. However, introduction of alkali and alkaline-earth metals to the calcium aluminate system significantly improves the glass-forming ability.4 On the basis of the above considerations, calcium aluminate glasses can be applicable to telecommunication uses. Renewed interests on these glasses have risen since stable formation of the +4 oxidation state of chromium dopant, which emits nearinfrared luminescence, has been known.5 Cr4+ ion under specific fourfold crystal fields in some oxide glasses emits 1.2–1.6 m fluorescence which is attributed to an intra-3d2 configurational transition. So far, formation of the stable +4 oxidation state of chromium has been achieved only in calcium-aluminate and alumino-silicate glasses.6,7 There is still lack of under-
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J. Mater. Res., Vol. 15, No. 2, Feb 2000 Downloaded: 06 Apr 2015
standing associated with the processing condition and mechanism of Cr4+ formation in glasses. For example, incorporation of Cr4+ into fourfold coordination sites was promoted when these glasses were melted under an inert atmosphere.6 However, the content
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