Fig. 1. Absorption and NIR emission of B0PS sample after fs laser irradiation. (a) Optical microscope image of grating under 6.0 μJ of fs laser pulse energy, and photographs of B0PS sample irradiated under different pulse energy (0–8.0 μJ, as labeled); (b) UV/VIS/NIR absorption and (c) NIR emission spectra (λex=808  nm) of the B0PS sample with increasing fs laser pulse energy; (d) dependence of Bi NIR emission intensity (red curve) and absorption coefficients (blue curve) on the pulse energy of the fs laser.

Fig. 2. Element migration, micro-Raman spectra, and visible fluorescence spectra in the fs laser-focused region. (a) Backscattering electron image and element distribution showing the relative concentrations of O, B, and Bi around the fs laser focal point; (b) micro-Raman spectra of the fs laser-focused region with different positions under 2.0 μJ of pulse energy. The Raman spectrum of the B0PS sample without fs irradiation is added for comparison (black curve). (c) XPS profiles at the Bi 4f core level of the B0PS sample before and after fs laser irradiation; (d) visible fluorescence spectra of the B0PS sample upon 354 nm excitation with laser pulse energy from 0 to 8.0 μJ.

Fig. 3. NIR emission and structure analysis of BxPS glasses without fs laser irradiation. (a) Emission (λex=808  nm), (b) FTIR, and (c) B11 MAS NMR spectra of BxPS glasses (x=0, 5, 15, 20, 25, 35, 45) before fs laser irradiation; (d) relative ratio of [BO4]/[BO3] in B11 MAS NMR and FTIR spectra, respectively, as a function of PbO content.

Fig. 4. Absorption, Bi NIR emission of BxPS glasses, and the sample 60B2O3–15SiO2–23PbO–2Sb2O3 without Bi2O3 before and after fs laser irradiation. (a) Absorption and (b) Bi NIR emission spectra (λex=808  nm) of the grating region of BxPS (x=0, 5, 15, 20, 25, 35, 45) glasses. The inset in (a) shows photographs of the BxPS sample after fs laser irradiation. (c) The dependence of emission intensity and peak position on PbO content (x=0–45); (d) XPS profiles at Pb and the Bi 4f core level of the B25PS sample before and after fs laser irradiation; (e) absorption and (f) emission spectra of the 60 B2O3–15SiO2–23PbO–2Sb2O3 sample without Bi2O3 before and after fs laser irradiation.

Fig. 5. Absorption, NIR emission, and visible luminescence of the B25PS irradiated sample after annealing. (a) Absorption, (b) NIR emission (λex=808  nm), and (c) visible fluorescence (λex=354  nm) of the irradiation region of the B25PS sample annealed at 400°C for 0, 5, 10, 20, 40, and 60 min, respectively. The inset in (b) shows the corresponding photographs of the B25PS sample. (d) The dependence of the Bi NIR emission intensity of the B0PS and B25PS samples on annealing time; (e) Bi NIR emission spectra of the B0PS and B25PS samples after first and second fs laser writing.

Fig. 6. Illustration of Bi-activated optical waveguide. (a) Optical microscope image of gratings inside the B25PS sample under 6.0 μJ laser pulse energy and the diffraction pattern of an He–Ne laser at 632.8 nm; (b) Bi NIR emission when pumping the waveguide under 808 nm irradiation (3  W/cm2).