Fig. 1. p-ZnO thin films and LED devices prepared by MOCVD method^[4]. (a) Schematic sketch of ZnO LED; (b) I-V characteristics of ZnO LED; (c) electroluminescence spectra of LED as a function of injected current at room temperature

Fig. 2. Schematic diagrams of band structures. (a) ZnMgO/ZnO^［7］;（b）ZnMgO/ZnMgBeO^［11］

Fig. 3. PL intensity obtained by adjusting well width and barrier height of ZnO/ZnMgO multi-quantum wells. (a) PL intensity at 16 K; (b) PL intensity at room temperature; (c) normalized PL intensity

Fig. 4. PL intensity of ZnO/ZnMgO multi-quantum wells with high internal quantum efficiency. (a) PL spectrum at 80 K of ZnO/Zn_0.9Mg_0.1O MQWs grown on GaN/Al₂O₃ substrate (inset shows integrated PL intensity of LE emission for MQWs as a function of temperature); (b) PL spectra at 300 K and 15 K of the ZnO/Zn_0.9Mg_0.1O MQWs grown on sapphire substrate

Fig. 5. Band structure of ZnO

Fig. 6. Results of perovskite luminescence. (a)(d) Statistical results of electroluminescence (EL) spectrum and external quantum efficiency (EQE) of red perovskite film LED^[117]; (b)(e) statistical results of EL spectrum and maximum EQE of green perovskite film LED^[118]; (c)(f) statistical results of EL spectrum and maximum EQE of sky blue perovskite film LED^[107]

Fig. 7. ASE results of perovskite thin films. (a)(e) ASE results of green perovskite thin films with PMMA surface passivation^[120]; (b)(f) ASE results of green perovskite thin films passivated in bottom and surface layers^[121]; (c) ASE results of green light perovskite thin films after optimization of crystal morphology^[122]; (d) ASE results of blue perovskite films; (g) ASE excitation results of red-green perovskite thin films; (h) ASE results of blue-green perovskite thin films^[123]

Fig. 8. Band structure, gap width, and absorption and fluorescence spectra of perovskite CsPbX₃. (a) Schematic diagram of CsPbX₃ band structure of perovskite^[124]; (b) schematic diagram of gap width of MAPbX₃^[126]; (c) composition dependent light absorption and fluorescence spectra of CsPbX₃ nanocrystalline halogen^[129]

Fig. 9. Luminescence properties of pure brominated perovskite nanoparticles and corresponding devices. (a) Low-power TEM and solution diagram of ultra-small CsPbBr₃ blue quantum dots of electrostatic double shell ^[133]; (b)(c) TEM and EL spectra of ultra-small CsPbBr₃ blue quantum dots after etching and ligand exchange treatment^[134]; (d) TEM image of CsPbBr₃ nanosheets^[135]; (e)(f) performance diagram of LED device with CsPbBr₃ nanosheet as luminescent layer

Fig. 10. Luminescence properties of pure brominated quasi-two-dimensional perovskite nanoparticles and corresponding devices. (a) Schematic diagram of quasi-two-dimensional perovskite structure and energy transfer^[139]; (b) schematic diagram of arrangement of different spacer molecules in quasi-two-dimensional perovskite^[140]; (c)(d) effect of coexistence of two spacer molecules on n value distribution and EL spectra of quasi-two-dimensional perovskite^[141]; (e)-(g) spectral contrast and LED performance before and after passivation of quasi-two-dimensional perovskite ^[142]

Fig. 11. Luminescence properties of mixed halogen-based perovskite nanoparticles and corresponding devices. (a) Fluorescence and UV-visible absorption spectra of chlorobromine mixed perovskite quantum dot solution after ligand passivation^[151]; (b) schematic diagram of surface defect passivation of chloro-bromine mixed perovskite quantum dots^[152]; (c) luminescence diagram of different content Ni⁺ doped chloro-bromine mixed perovskite quantum dots^[153]; (d)(e) comparison of LED performance of chloro-bromine mixed perovskite quantum dots before and after Ni⁺ doping^[153]

Fig. 12. Luminescence properties of mixed halogen-based perovskite and corresponding devices. (a) Schematic diagram of passivation of quasi-two-dimensional perovskite ligand^[174]; (b) effect of different spacer molecules on n value of two-dimensional perovskite^[175]; (c) schematic diagram of quasi-two-dimensional perovskite LED devices prepared by different spacer molecules^[176]; (d) schematic diagram of quasi-two-dimensional perovskite bandgap width with different chloro-bromine ratios^[180]