Dual-Emitting Mn4+/Mn5+ in Ba6Na2Nb2P2O17 phosphors for enhanced NIR-I and NIR-II spectroscopy applications

• NIR-I and NIR-II emission can be achieved separately or simultaneously using Mn 4+ / Mn 5+ doping. • Energy transfer between dopants is studied as a function of dopant concentration. • The sites for the Mn dopants in host are identified by optical spectroscopy , DFT calculations and EPR spectroscopy . • Both bio-penetration capabilities and non-invasive NIR-II imaging are demonstrated in a proof-of-concept experiment. The dual/multimodal imaging capability of combining NIR-I (650 − 900 nm) and NIR-II (1000 − 1700 nm) emission from a luminescent material offers complementary advantages for versatile applications such as nondestructive detection and biological imaging. However, realizing simultaneous emission with both NIR-I and NIR-II within a single-component remains a critical challenge. Herein, a strategy is presented by utilizing localized isolation to form two separated luminescent centers in Ba 6 Na 2 Nb 2 P 2 O 17 : Mn 4+ /Mn 5+ (BNNPO) compound, where Mn 4+ exhibits a broad emission centered at 750 nm (NIR-I) under 365 nm excitation, and Mn 5+ produces a narrow emission centered at 1180 nm (NIR-II) under 650 nm excitation. Interestingly, NIR-I and NIR-II can be simultaneously excited by 330 − 450 nm. Systematic experiments and Density Functional Theory calculations (DFT) including formation energy analysis reveal that Mn 4+ occupies octahedral Nb 5+ sites, while Mn 5+ substitutes at tetrahedral P 5+ sites. Meanwhile, the energy transfer from Mn 4+ to Mn 5+ allows Mn 5+ to be excited by both blue and red light. Finally, a NIR phosphor-converted light-emitting diode (pc-LED) was fabricated. A proof-of-concept experiment was conducted to validate bio-penetration capabilities and non-invasive organic material detection. This work provides valuable insights for exploring dual/multimodal NIR phosphors in luminescent imaging applications.