Three-dimensional luminescence tomographic visualization of biological tissues

We propose a method for obtaining a fluorescence tomographic image for visualization and diagnosis of tissues of a living organism. The method is based on the excitation of the luminescence of multicolor upconverting nanoparticles localized in the depth of the biological tissue or a phantom imitating it by IR light. By recording the changes in the shape of the spectrum of the intensity of luminescence radiation from luminescent nanoparticles on the surface of the tissue, it is possible to obtain information about the depth of their occurrence. To implement this approach, upconverting nanoparticles were synthesized on the base of $\beta$-NaYF$_4$ crystal matrix doped with rare-earth elements Yb$^{3+}$, Er$^{3+}$, and Tm$^{3+}$. The luminescence spectra of the produced nanoparticles upon excitation at a wavelength of 980 nm contain three narrow bands with maxima at wavelengths 540, 655, and 800 nm.