Fig. 1. Schematic diagram of structure design for binary orthogonal excitation-emission systems

Fig. 2. Binary orthogonal excitation-emission systems for orthogonal dual-color upconversion luminescence. (a) Schematic illustration of core/quadruple-shell NaGdF₄:Yb/Tm@NaGdF₄@NaYbF₄:Nd@Na(Yb,Gd)F₄:Ho@NaGdF₄ with blue-green dual-color orthogonal luminescence and its corresponding emission spectra and photographs under 980/808 nm binary excitations^[41]; (b) schematic illustration of core/triple-shell NaYF₄:Nd/Yb/Tm@NaYF₄:Nd@NaYF₄@NaYF₄:Yb/Er with blue-green dual-color orthogonal luminescence and its corresponding emission spectra and photographs under 980/808 nm binary excitations^[33]; (c) schematic illustration of core/quintuple-shell NaGdF₄:Yb,Er@NaYF₄:Yb@NaGdF₄:Yb,Nd@NaYF₄@NaGdF₄:Yb,Tm@NaYF₄ with excitation power density-independent blue-green high-pure dual-color orthogonal luminescence and its corresponding emission spectra and photographs under 980/796 nm binary excitations^[42]; (d) emission spectra of core/quadruple-shell NaGdF₄:Yb,Er@NaYF₄@NaYF₄:Yb, Tm@NaYbF₄:Nd@NaYF₄ with varied thickness of an NaYF₄ interlayer under 808/980 nm binary excitations^[43]. (a) Reproduced with permission ref. [41]. Copyright 2013, Wiley-VCH; (b) reproduced with permission ref. [33]. copyright 2014, Wiley-VCH; (c) reproduced with permission ref. [42]. copyright 2016, Wiley-VCH; (d) reproduced with permission ref. [43]. copyright 2017, American Chemical Society.

Fig. 3. Binary orthogonal excitation-emission systems with orthogonal dual-color emissions. (a) Schematic illustration of Er³⁺ sensitizer-based core/triple-shell NaYF₄:Er@NaYF₄@NaYF₄:Yb/Tm@NaYF₄ with green-blue dual-color orthogonal emissions and its corresponding emission spectra and photographs under 1532/980 nm binary excitations^[44]; (b) schematic illustration of red-emitting NaErF₄:Tm core-based multilayer core-shell nanostructures and their corresponding photographs under 1550 nm and 980/808 nm binary excitations^[20]; (c) schematic illustration of self-sensitization of Er³⁺-based core/double-shell NaYF₄:Er@NaYF₄@NaYF₄:Yb/Tm with blue-green dual-color orthogonal emissions and its corresponding emission spectra under 808/940 nm binary excitations^[45]; (d) schematic illustration of red-emitting NaErF₄ core-based core/triple-shell NaErF₄@NaYF₄@NaYbF₄:Tm@NaYF₄ with red-blue dual-color orthogonal emissions and its corresponding emission spectra and photographs under 808/980 nm binary excitations^[46]; (e) schematic illustration of a single-emissive layer-based core/double-shell NaErF₄:Yb/Tm@NaYF₄:Yb@NaNdF₄:Yb with red-green dual-color orthogonal emissions and its corresponding emission spectra and photographs under 980/808 nm binary excitations^[47]; (f) schematic illustration of a single-emissive layer-based binary orthogonal excitation-emission systems (NaYF₄:Yb/Er/Mn@NaYF₄:Yb@NaNdF₄:Yb) and its corresponding emission spectra and photographs under 980/808 nm binary excitations^[49]. (a) Reproduced with permission ref. [44]. Copyright 2018, Wiley-VCH; (b) reproduced with permission ref. [20]. Copyright 2019, Wiley-VCH; (c) reproduced with permission ref. [45]. Copyright 2018, Royal Society of Chemistry; (d) reproduced with permission ref. [46]. Copyright 2018, American Chemical Society; (e) reproduced with permission ref. [47]. Copyright 2019, Nature Publishing Group; (f) reproduced with permission ref. [49]. Copyright 2020, Wiley-VCH

Fig. 4. Schematic diagram of structure design for ternary orthogonal excitation-emission systems

Fig. 5. Ternary orthogonal excitation-emission systems for orthogonal three-primary-color upconversion luminescence. (a) Schematic illustration of core/quintuple-shell NaYF₄:Yb/Tm@NaYF₄@NaYF₄:Er/Ho@NaYF₄@NaYF₄:Nd/Yb/Er@NaYF₄:Nd with excitation power density-independent red-green-blue high-pure three-primary-color orthogonal emissions and its corresponding emission spectra and photographs under 1560/808/980 nm ternary excitations^[52]; (b) schematic illustration of core/sextuple-shell LiYbF₄:Tm@LiGdF₄@LiGdF₄:Yb/Er@LiYF₄:Nd/Yb@LiGdF₄@LiErF₄:Tm@LiGdF₄ with excitation power density-independent orthogonal three-primary-color luminescence and its corresponding emission spectra and photographs under 1532/980/800 nm ternary excitations^[59]; (c) transmission electron microscopy image and schematic illustration of core/septuple-shell NaErF₄@NaYF₄@NaGdF₄:Yb/Er@NaGdF₄:Yb@NaGdF₄:Nd/Yb@NaYF₄@NaGdF₄:Yb/Tm@NaYF₄ with excitation power density-independent orthogonal three-primary-color luminescence and its corresponding emission spectra and photographs under 1532/808/980 nm ternary excitations^[60]. (a) Reproduced with permission ref. [52]. Copyright 2021, American Chemical Society; (b) reproduced with permission ref. [59]. Copyright 2021, American Chemical Society; (c) reproduced with permission ref. [60]. Copyright 2021, Nature Publishing Group.

Fig. 6. Applications of orthogonal excitation-emission systems

Fig. 7. Typically applications of orthogonal excitation-emission systems in the fields of optical storage, security anticounterfeiting and displays. (a) Binary orthogonal excitation-emission system for NIR-guided optical data storage^[44]; (b) binary orthogonal excitation-emission system for multi-level anti-counterfeiting^[42]; (c) ternary orthogonal excitation-emission system for information encryption and decryption^[52]; (d) ternary orthogonal excitation-emission system for advanced anti-counterfeiting^[58]; (e) binary orthogonal excitation-emission system for multi-dimensional anti-counterfeiting^[43]; (f) ternary orthogonal excitation-emission system for 2D color display^[59]. (a) Reproduced with permission ref. [44]. Copyright 2018, Wiley-VCH; (b) reproduced with permission ref. [42]. Copyright 2016, Wiley-VCH; (c) reproduced with permission ref. [52]. Copyright 2021, American Chemical Society; (d) reproduced with permission ref. [58]. Copyright 2022, American Chemical Society; (e) reproduced with permission ref. [43]. Copyright 2017, American Chemical Society; (f) reproduced with permission ref. [59]. Copyright 2021, American Chemical Society

Fig. 8. Typically applications of orthogonal excitation-emission systems in the fields of sensing and biomedicine. (a) Binary orthogonal excitation-emission system for the detection of TNT residues in the fingerprint^[49]; (b) binary orthogonal excitation-emission system for the detection of aflatoxin B1^[48]; (c) binary orthogonal excitation-emission system for super-resolution image^[45]; (d) binary orthogonal excitation-emission system for imaging-guided combined photodynamic therapy/ chemotherapy^[42]. (a) Reproduced with permission ref. [49]. Copyright 2020, Wiley-VCH; (b) reproduced with permission ref. [48]. Copyright 2021, American Chemical Society; (c) reproduced with permission ref. [45]. Copyright 2021, Royal Society of Chemistry; (d) reproduced with permission ref. [42]. Copyright 2016, Wiley-VCH.