Tailored emission of Ho3+- Cu2+ doped lead Boro phosphate glasses for light source in NIR imaging applications

Tailoring the wavelength of lanthanide sources with transition metal oxides as luminescent probe for luminescence and NIR imaging is still challenging in medical field. In this context, the role of copper ions was analyzed in tailoring the wavelength of emission in melt quenched series of copper doped holmium lead Boro phosphate glasses. To confirm the amorphous nature, the series of glasses were characterized by XRD. To realize the symmetrical and asymmetrical vibrations in glasses to support luminescence, the FTIR studies were carried out for the samples. The traces of DTA demonstrated thermal stability and the XRD analyses demonstrated the nature of all the glasses as amorphous character. The ground state orbital is d(xy)(2)(B-2(1g)) for Cu2+, and the ligand environment around Cu2+ is made up of tetragonally distorted octahedral sites, according to the Spin-Hamiltonian parameters (SHP) of the EPR spectra. The Cu2+-Ho3+ ions co-doped glass's absorption spectra revealed surface plasmon resonance (SPR) for Cu2+ ions at about 537 nm. The B-2(1g) -> B-2(2g) transition is attributed to the distinctive broad bands observed in the optical absorption spectra. Ho3+ ions are responsible for ten absorption transitions in the visible-NIR regions of the optical absorption spectrum. Furthermore, the octahedral absorption transition between B-2(1g) (D) -> B-2(2g) (D) of the Cu2+ ions was discovered to be responsible for a strong transition in the visible spectrum at about 864 nm. The luminescence spectra of glasses containing Cu ions have shown a peak at around 765 nm, owing to octahedral lattice of Cu2+ ions. Among all the emission transitions of Ho3+ ions, the S-5(2) + F-5(4) -> I-5(7) (763 nm) transition intensity was enhanced when compared to that of Cu2+ ions free glass, with a progressive increase in CuO mol%. The data analysis suggests that there is an increase in the energy transfer from octahedral Cu2+ ions to Ho3+ ions (Cu2+ -> Ho3+) at mol% of 0.5 (HC5). The time decay curves at 763 nm also supported the proposed energy transfer mechanism. Hence the synthesized glass HC5 can be a potential candidate for 763 nm light source for NIR imaging.