Investigation of the Mechanisms Responsible for the Formation of Intrinsic and Impurity-Related Electron and Hole Trapping Centers by Measuring the Reflectance, Emission, and Excitation Spectra of YPO4:Bi

In YPO4:Bi irradiated with photons in the energy range of 5.5–6.2 eV and with X-rays, sensitization-related luminescent states are formed in the 4.43–3.35 eV energy range, appearing as a broad emission band. The excitation spectrum of this broad band lies in the photon-energy range of 5.9–6.2 eV. As in many phosphor materials, these sensitization-related luminescent states are formed as a result of charge transfer from an excited host anion to neighboring ions and impurity centers introduced into the lattice, leading to the formation of electron-trapping centers. Upon excitation of irradiated YPO4:Bi with photons in the energy range of 4.43–3.35 eV, two groups of emission bands are observed: at 3.1–2.9 eV and at 2.8–2.25 eV. These emissions are excited within two spectral regions, from 4.43 to 3.8 eV and from 3.7 to 3.25 eV, and appear as several recombination-related bands. Reflectance spectrum measurements show that, within the transparency region of the host matrix, additional energy levels appear in the 4.43–3.35 eV spectral range. Excitation through these levels gives rise to the observed recombination luminescence, and their energy positions correspond to the excitation spectra of the respective recombination emission bands.