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(a) XRD patterns of the Tm3+-doped PG and GC heat-treated at 580 °C for 2 h, (b) TEM micrograph of GC:Tm3+, (c) the size distribution of CaF2 nanocrystals embedded in glass matrix, and (d) HRTEM image taken from the circle region of the TEM micrograph. The inset of Fig. 1(a) shows the optical images of GC:Tm3+ and GC:Tm3+,Yb3+ over a printed paper sheet, and that of Fig. 1(b) presents the corresponding SAED pattern of GC:Tm3+.
NIR PL spectra of GC:Tm3+ and GC:Tm3+,Yb3+. Solid lines represent NIR PL spectra recorded on a R5509-72 PMT with a 450 W Xe lamp as excitation source, and short dash lines are those determined on a PbSe detector with an 808 nm LD (Fig. 2(b)) and a 976 nm LD (Fig. 2(c)) as excitation sources. The inset of Fig. 2(a) shows visible PL spectrum of GC:Tm3+ excited at 468 nm with a 450 W Xe lamp excitation source.
PLE spectra of the GC:Tm3+ sample monitored at PL wavelengths of 650, 790, 1190, 1460, and 1612 nm, respectively.
Schematic energy-level diagram indicating the concept of a three-step sequential three-photon NIR-QC (a) via 468 and 790 nm directly exciting Tm3+ in GC:Tm3+, respectively, and (b) with 976 nm LD pumping Yb3+ to excite Tm3+ through a Stokes ET in GC:Tm3+,Yb3+.
Visible (a) and NIR (b) time-resolved fluorescence spectra of GC:Tm3+ upon 468 nm pulsed light excitation with a microsecond μF900 Xe flash lamp.
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