Bright and Efficient Sensitized Near-Infrared Photoluminescence from an Organic Neodymium-Containing Composite Material System

Abstract

Intense organic neodymium (Nd3+) emission is obtained with near-infrared (NIR) emission equivalent in intensity to that of an organic semiconductor emitting material. The advantage of Nd3+ emission is its narrow line width and NIR emission, which is enhanced by ∼3000 times at low excitation power through an efficient sensitization effect from a composite organic sensitizer. This performance is optimized at high concentrations of Nd3+ ions, and the organic perfluorinated system provides the ion excitations with a quantum efficiency of ∼40%. The material system is applicable to thin films that are compatible with integrated optics applications.

Structural and Luminescent Features of Lanthanide Ate Complexes with Polychlorinated 2-Mercaptobenzothiazolate Ligands

“…Because the mbt Cl n ligands demonstrate similar absorption behavior (Figure S12), it should be concluded that such a significant difference in the NIR PL intensities is additionally caused by differences in energy transfer. In a recent work by Gillin et al, it was shown that the value of the ligand triplet level of 19 000 cm –1 is optimal for the energy transfer to the 4 G 5/2 state of neodymium. Indeed, the resonant energy transfer in this case is more favorable because of the overlap of the phosphorescence spectra of the respective chlorinated benzothiazole, and the PL excitation spectra of Nd emission in 1 and 4 are much higher in the case of the mbt Cl4 derivative (Figure S11b,c) due to the increased contribution of the most intense Nd transition of 4 I 9/2 → 4 G 5/2 .…”

“…Therefore, the generally accepted strategy for designing highly NIR-emissive lanthanide substances is to eliminate O–H and N–H bonds from the ligand structure and to replace C–H bonds with carbon–halogen bonds . Currently, the main focus in this field is to develop a perfluorinated environment for lanthanide-based NIR emitters. − While the application of heavier halogens for this purpose is rare, recent reports suggest that they may increase the sensitization efficiency …”

Organic Holmium(III) Complexes as a Potential Bright Emitter in Thin Films

“…For example, measuring the 1.5 μm emission brightness of most organic erbium materials is challenging. Within numbers of those sensitization materials, a composite system of a chromophore, Zn­(F-BTZ) 2 and a perfluorinated organic complex, Ln­(F-TPIP) 3 (Ln = Nd, Er, and Yb) has a tremendous sensitization effect that provides the ion NIR emission with up to an enhancement factor of 10 4 times. − In this system that has Zn­(F-BTZ) 2 and Ln­(F-TPIP) 3 molecules mixed at the molecular level, the average separation of the two molecules is believed to be within a range of ∼1 to 2 nm, which is approximately the size of the molecule. − Meanwhile, the perfluorinated organic environment and bulky ligand cage significantly protect the ions from the quenching effect. Dispite this success, the emitting region has only extended to an ∼1.5 μm band with an internal quantum efficiency of ∼30% .…”

“… 23 − 25 In this system that has Zn(F-BTZ) 2 and Ln(F-TPIP) 3 molecules mixed at the molecular level, the average separation of the two molecules is believed to be within a range of ∼1 to 2 nm, which is approximately the size of the molecule. 25 − 27 Meanwhile, the perfluorinated organic environment and bulky ligand cage significantly protect the ions from the quenching effect. Dispite this success, the emitting region has only extended to an ∼1.5 μm band with an internal quantum efficiency of ∼30%.…”