Full-color laser displays based on organic printed microlaser arrays

Laser displays, which exploit characteristic advantages of lasers, represent a promising next-generation display technology based on the ultimate visual experience they provide. However, the inability to obtain pixelated laser arrays as self-emissive full-color panels hinders the application of laser displays in the flat-panel sector. Due to their excellent optoelectronic properties and processability, organic materials have great potential for the production of periodically patterned multi-color microlaser arrays. Here, we demonstrate for the first time full-color laser displays on precisely patterned organic red-green-blue (RGB) microlaser matrices through inkjet printing. Individual RGB laser pixels are realized by doping respective luminescent dyes into the ink materials, resulting in a wide achievable color gamut 45% larger than the standard RGB space. Using as-prepared microlaser arrays as full-color panels, we achieve dynamic laser displays for video playing through consecutive beam scanning. These results represent a major step towards full-color laser displays with outstanding color expression.

The dispersed droplets were dried in air for one day before optical characterization.
In comparison with the ink droplets, the dried spherical caps exhibit obvious volume shrinkage. We compared the structural parameters of an identical spherical cap before and after drying ( Supplementary Fig. 3). The ink droplet dispersed on the hydrophobic substrate exhibit a geometry of spherical cap ( Supplementary Fig. 3a), and the height and radius can be determined to be 64.32 and 108.83 μm ( Supplementary Fig. 3b), respectively. Assuming that the dispersed ink droplet has a perfect spherical cap geometry, we calculated the volume to be 1.135×10 6  In order to clarify the drying mechanism, we recorded the masses of dispersed ink droplets at different time, which are presented in Supplementary Fig. 3e. The mass decreases as time elapses in the first 1.5 hours and stabilizes in the subsequent several hours. The initial sharp reduction in mass should be attributed the water evaporation of inks because of negligible weight loss from other two constituents of the inks (BSA and glycerin). Therefore, the underlying drying mechanism of the ink droplets is ascribed to the evaporation of water contained in the inks.  μm, when the applied tip diameter was 10, 20, 30, 40, 50 and 60 μm, respectively, revealing a monotonous increase with increasing needle tip diameter. Therefore, the size of the microcavities can be roughly controlled at the micrometer scale by changing the glass needle tip diameter. These results all indicate that the printed spherical caps are highly reproducible, which is beneficial for constructing high-quality and large-area spherical cap microlaser arrays as display panels. We prepared a closely-packed spherical cap array ( Supplementary Fig. 10) using a glass needle with a tip diameter of 5 μm. In geometry, close-packing of equal spherical caps is a dense arrangement of congruent spherical caps in an infinite, regular arrangement (or lattice). Each spherical cap (with a base diameter of 6.5 μm) has six neighbors, and the center-to-center spacing of adjacent spherical caps is a simple honeycomb-like tessellation with a pitch (distance between spherical caps centers, 7.1 μm). Thus, the pack density should be the fraction of space occupied by the spherical cap in the lattice, which is exhibited in the Supplementary Fig. 10     The lasing performances of the dye-doped spherical caps were examined using a custom microphotoluminescence system. A 355-nm femtosecond laser (Spectra-Physics, TOPAS) was employed as the excitation source, and the excitation energy was altered using neutral density filters. The PL signal was collected with an objective (Nikon CFLU Plan, 20×, N.A.=0.5). After passing through the corresponding filters (400-nm long-pass), the collected emissions were dispersed with a grating (1200 G mm -1 ) and the recorded using a thermal-electrically cooled CCD (Princeton Instruments, ProEm 1600B). were calculated from the corresponding spectra. Figure 15b shows the obtained five coordinates on a CIE1931 color diagram. All five colors are located along the dashed line, which is defined by connecting the spots extracted from the blue (Fig. 15a, top) and green (Fig. 15a bottom)  identical to the one shown in Fig. 4b. This figure demonstrates the ability to display arbitrary numbers and characters using the as-developed display system, which can be applied to show desired text information.

Supplementary Tables
Supplementary The saturation and contrast of laser displays are inherently higher than those of current display technologies because colors generated by combining RGB laser sources with narrow spectral lines are more vivid than those generated by broadband light sources 2 . Supplementary Fig. 16 illustrates the CIE1931 chromaticity color diagram of a printed RGB laser pixel and the standard RGB (sRGB), which is widely used in industry 3 . The corresponding chromaticity coordinates (x, y) are given in Supplementary Table 2.
To compare the color gamut of our RGB pixel with that of the sRGB, we calculated their color gamuts after converting to a perceptually uniform color space (CIE1976).
The chromaticity coordinates (u', v') in CIE1976 summarized in Supplementary Table   3 The three sets of color coordinates constitute a triangle in the CIE color diagram.
All colors in the triangle can be displayed by proper mixing of the three primary colors. The area of the RGB triangle (A) can be calculated according to Supplementary The areas of the RGB pixel and sRGB were calculated to be 0.0941 and 0.0649, respectively. Therefore, the printed RGB laser pixel covers 45% more perceptible colors than the standard RGB 6 .