Fig. 1. Laser direct writing induced nanocrystals inside glass^[57]. (a) Photoluminescence (PL) peak intensity of CsPbI₃ nanocrystals excited by a 405 nm UV light with different pulse widths; (b) PL spectra of CsPbI₃ nanocrystals under laser pulse width of 230 fs-4 ps(laser fluence of 19.2 J/cm², repetition frequency of 100 kHz, and irradiation time of 800 ms)

Fig. 2. Ultrafast laser direct writing optical photos of CsPbI₃ nanocrystal trajectory lines and corresponding UV excited fluorescence photos (at a fixed average laser power, the laser repetition frequency of 20, 30, 40, 50, 60, and 70 kHz, corresponding to pulse energy of 28.6, 19.2, 14.3, 11.5, 9.55, and 8.19 J/cm², writing speed is 10 µm/s)^[56]

Fig. 3. Laser scanning line diagram^[59]. (a) Schema of laser spot moving from point A to point B with the distance from point A to point B is greater than the diameter of the laser spot after focusing; (b) temperature-time profiles at point A at different pulse energies E_1(red)>E_2(yellow)>E_3(blue)

Fig. 4. Photoluminescence spectra and corresponding photoluminescence photos of precipitated nanocrystals obtained by laser direct writing under different irradiation time T_i^[68]

Fig. 5. Schematic of ultrafast laser-induced liquid nanophase separation and formation of nanocrystals^[68]

Fig. 6. PL spectra of CsPb_xCd_1-xBr₃ nanocrystals written in one piece of glass under different ultrafast laser static irradiation parameters (excitation light source wavelength is 405 nm)^[74]

Fig. 7. Direct writing control of nanocrystalline luminescent band gap^[68]. (a)‒(c) Zhejiang University emblem with different colors written directly inside the glass; (d)‒(f) nanocrystalline color pattern direct writing

Fig. 8. Micron level color micro-LED display devices^[68]. (a) Experimental setup image for the micro-LED devices (inset I is GaN micro-LED arrays, inset II is lighted blue micro-LED arrays); (b) an enlarged version of Fig. 8(a); (c) photo of the red emission array inside the glass under blue light excitation

Fig. 9. Applications in display^[68]. (a) 3D holographic display; (b) 2D dynamic display

Fig. 10. Nanocrystalline patterns for information encryption using ultrafast laser direct writing^[74]. (a) Multiple encryptions with patterning QR code (scale is 50 μm, excitation light wavelength is 405 nm); (b) pattern encryption (no significant differences in daylight but displayed different regions with green and blue under 405 nm UV light, scale bar is 100 μm)