The methods of vacuum ultraviolet and thermal activation spectroscopy were used to measure the excitation spectra of impurity radiation in the fundamental absorption band of K2SO4-Cu crystals at 15 K and 300 K. An energy transfer was detected from the base to Cu+ impurities. The band gap of crystals K2SO4 was estimated. In K2SO4-Cu crystals, recombination radiation bands were detected at 2.95 ÷ 3.0 eV corresponding to electron hole capture centers.

Intrinsic and extrinsic nature of the luminescence of pure and Eu³⁺ and Tb³⁺ rare-earth ions activated mesoporous silica has been investigated by spectroscopic methods. Increasing the Eu³⁺ impurity concentration from 0.01 mg to 7 mg, results in an increase of the impurity particles radiation in the luminescent mesoporous colloidal silica (LMCS) matrix by several times. With an increase in the concentration of Tb³⁺ from 0.01 mg to 3 mg, impurity luminescence intensity increases several times while the intrinsic luminescence intensity maximum at 400 and 460 nm is decreasing. Based on the experimental evidence, it is suggested that the energy of the own electronic matrix excitation is transferred by emitters, i.e., impurities of Eu³⁺ and Tb³⁺ ions. Also, it is assumed that the emission band at 610 nm in an LMCS—Eu³⁺ and emission band at 543 nm in the LMCS—Tb³⁺ is attributed to the intracenter transitions within the Eu³⁺ and Tb³⁺ ions.

This study of the BaSO₄-Bi phosphor has revealed that the accumulated energy after external optical excitation exhibits specific characteristics. During irradiation with photon energy exceeding the bandgap, in addition to the intrinsic ultraviolet emission of the Bi³⁺ ion, several recombination emissions and emission from the Bi²⁺ ion are observed. At 80 K, the recombination luminescence states and Bi²⁺ ion emission form combined electronic states. Upon heating of the BaSO₄-Bi phosphor, these combined electronic states decay into recombination emissions at 2.34 eV, 2.4 eV, 3.1 eV, and 2.7 eV, as well as Bi²⁺ ion emission at 1.97 eV. It is assumed that the 2.34 eV, 2.4 eV, and 3.1 eV emissions are associated with the recombination of electrons released from ionized ${SO}_4^{3-}$ electron trapping centers with nonequivalently localized holes in the host lattice. The 2.7 eV emission is attributed to the decay of an exciton formed by electron–hole recombination near a Bi³⁺ ion.

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.