Charge Transfer Luminescence of Yb3+

L. van Pieterson et al. / Journal of Luminescence 91 (2000) 177–193 187Fig. 15. Decay time (*), on the left axis, and CT luminescenceintensity at 420 nm (&) and at 822 nm (n), on the right axis, ofLa 2 O 2 S doped with Yb 3+ as a function of temperature.SPEX 1680 spectrofluorometer. Fig. 14 shows theemission and excitation spectra of Y 2 O 2 S:Yb 3+and La 2 O 2 S:Yb 3+ at 10 K. In Y 2 O 2 S, Yb 3+charge transfer luminescence is observed at 390and 612 nm. The energy difference between theCT bands is 9500 cm 1 , close to the expected10 000 cm 1 . The FWHM of the bands is about3500 cm 1 . In the excitation spectrum the chargetransfer band is observed at 309 nm so the Stokesshift is relatively small, about 6000 cm 1 . Thedecay time measured at 390 nm is about 250 ns.The Y 2 O 2 S host lattices luminesce at 318 nm whenexciting into the conduction band (l5260 nm).This emission quenches already below 50 K. Also abroad defect-related emission around 590 nm isobserved which quenches at about 275 K.In La 2 O 2 SYb 3+ CT luminescence is observed at439 and 759 nm, the energy difference betweenthese bands is 9500 cm 1 . The CT excitation bandis observed at 317 nm, giving a Stokes shift ofapproximately 8500 cm 1 . In Fig. 15, the intensityof the Yb 3+ CT luminescence in La 2 O 2 S and itsdecay time are given as a function of temperature.From this figure we can estimate the quenchingtemperature at 150 K. Table 7 summarizes theluminescence properties of the oxysulfide hostlattices and Yb 3+ -doped samples.Fig. 14. Emission (for l exc ¼ 240 nm) and excitation (forl em ¼ 393 nm) spectra of Y 2 O 2 S doped with 1% Yb 3+ (a, b)and emission (for l exc ¼ 270 nm) and excitation (for l em ¼460 nm) spectra of La 2 O 2 S (c, d) doped with 1% Yb 3+ ,T ¼ 10 K.3.5. FluoridesFig. 16 shows the emission and excitationspectrum of LiYF 4 doped with 3% Yb 3+ . Theemission spectrum has been recorded using gateddetection (delay 5 ns, gate 10 ns) and shows two