Compositional dependence of infrared to blue and red conversion luminescence in oxyfluoride glass-ceramics co-doped with
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The upconversion of infrared radiation into visible light has been studied in heavy metal oxyfluoride glass-ceramics co-doped with Yb 3+ and Tm3+ ions at 300 K. The general composition of the compounds is 69.9PbF2 + 7.5WO3 + 7.5MO2 + 15YbF3 + 0.1TmF3 (M = Si, Ge, Zr, Te, and Th). Two main upconversion emissions were observed. They are centered at 477 and 775 nm, corresponding to the XG* —> 3 H 6 and 3 F 4 — 3 F 4 —» 3 F 3 —» 3 F 2 — JG4 (Yb) 2 F 7 / 2 - 2 F 5 / 2
1650 1220 780 690 660 465 966
6060 8196 12820 14493 15151 21505 10352
homogeneously on a bronze plate with a cavity of 30 mm 2 surface area and 1 mm depth for fluorescence measurements. The excited area of the sample was 4 mm 2 . Absorption spectra were recorded by using a double beam Cary 17 spectrophotometer. Emission and excitation spectra were measured by exciting the samples with light from a 250 W tungsten halogen lamp passed through a Jobin-Yvon IR-H20 monochromator and an RG 850 nm long pass filter. The fluorescence signals were analyzed with an HR 1000 Jobin-Yvon monochromator equipped with an RTC 56 TVP photomultiplier in the visible region and a silicon photodiode type PIN-10DP in the IR region. For the time dependences of upconverted emissions, a General Radio flash lamp with an RG 850 nm long pass filter was used as the excitation source. The signal detected with an RTC 56 TVP photomultiplier was recorded with a digitizer, then was processed with a computer. The decay time of the 1G4 level was measured under a direct excitation in this level. The excitation was provided by a dye laser (Molectron, Model DL-100) pumped by a nitrogen laser (Sopra, Model N.2100). The signal was analyzed by a photomultiplier connected to a Boxcar Integrator (PAR model 162). The emission spectra used to calculate the absolute quantum efficiencies were corrected for the wavelength variations in the system response by calibrating the monochromator-photomultiplier unit with a standard tungsten halogen lamp.
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15 UJ 111
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01 FIG. 2. Energy level diagram of Tm 3+ and Yb 3+ ions in PWTeYbTm glass-ceramic and the upconversion routs upon infrared excitation.
T=300K 20
Excitation power; 16.5 mW/cm 2 X=966nm
15f
XI
III. RESULTS AND DISCUSSION The absorption spectrum of the PWTeYbTm glassceramic recorded at 300 K is presented in Fig. 1. The bands observed are due to the transitions of Tm3+ and Yb 3+ from their ground state to the excited states, and they are in agreement with those previously reported for Tm3+ in fluoride glasses.13 The energy of the barycenter of the absorption bands is presented in Table II and Fig. 2. Two main upconversion emissions of Tm3+ (red and blue) in the PWTeYbTm sample observed in the visible region upon 966 nm excitation are shown in Fig. 3 as 2140
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500
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WAVELENGTH (nm) FIG. 3. Upconversion emission spectrum of PWTeYbTm glassceramic measured upon 966 nm excitation at 300 K.
J. Mater. Res., Vol. 9, No. 8, Aug 1994
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J. P. Denis et al.: Co
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