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The effect the doping of Zn2 – 2xMn2xSiO4 (х ≤ 0.2) luminophor with magnesium has on the charge state of manganese and the nature of the quenching of luminescence is examined. It is estimated that introducing magnesium ions and raising their content in the cationic sublattice of the crystal phosphor stabilizes manganese in the doubly charged state. It is shown that the concentration quenching of luminescence is in this case due only to the clusterization of doubly charged manganese ions.

The analysis of the unified series of single-phase Zn2 – 2xMn2xSiO4 samples (x ≤ 0.2) has provided the possibility to determine the optimal dopant concentration x = 0.13 for the maximum luminescence intensity. It has been established that the dominating mechanism of concentration luminescence quenching and excitation energy dissipation is the oxidation of some Mn2+ activating ions and the growth of defectness in the luminophore due to this process Phosphors.

The region of homogeneity in a solid solution of the nominal composition Zn2 – 2xMn2xSiO4 (х ≤ 0.21 ± 0.01) is determined. A comparison of the values of the pycnometric and X-ray densities for the compositions with x ≥ 0.13 ± 0.01 indicates the coexistence of manganese ions in two charge states: Mn2+ and Mn3+. It is established voltammetrically that all of the manganese ions in Zn1.8Mn0.2SiO4 are divalent, and the concentrations of Mn2+ and Mn3+ ions in Zn1.6Mn0.4SiO4 are comparable. The oxidation of some Mn2+ ions results in the concentration quenching of luminescence in Zn2 – 2xMn2xSiO4 solid solutions at х > 0.13 ± 0.01.

Investigation of magnetic susceptibility and electron paramagnetic resonance of the samples from the region of solid solution Zn2–2xMn2xSiO4 shows that at x ≤ 0.1 the oxidation state of all manganese ions is +2. At x ≥ 0.2, manganese is present as Mn2+ and Mn3+. Crystal-chemical studies show that defect formation mechanism changes for 0.1 ≤ x ≤ 0.2. Oxidation of part of Mn2+ ions at x > 0.1 causes luminescence concentration quenching in this region of x.

In the present study, the willemite-based Zn2-2xMn2xSiO4 solid solution has been produced by the high-temperature solid-state reaction. The powder samples were characterized by X-ray diffraction, UV–vis spectroscopy and optical emission spectroscopy. A monotonic increase in the luminescence intensity is observed with a growth of the Mn content, but not exceeding x = 0.13. The absence of concentration quenching of luminescence below this limit is explained by stochastic arrangement of the dopant atoms, which is confirmed by crystallographic data. Basic trends in distribution of Mn ions within the willemite lattice and electronic properties were validated by means of DFT calculations. Homogenous distribution of photoactive substituent ion is a key feature in the design of luminescent materials.

Single-phase luminophor Zn2SiO4:V with willemite structure is prepared by hydrothermal method. It is found that the Zn: Si: V ratio between cations is 2: 0.9: 0.1. It is shown that the inclusion of vanadium in the willemite structure reduces the width of the bandgap by ΔE g ≈ 2 eV. Using a combination of spectroscopic and voltammetric techniques, it is found the zinc silicate matrix contains vanadium ions with charge states V5+, V4+, and V3+. In addition, magnetic ions form clusters.

A promising yellow phosphor, α-Zn2V2O7, was synthesized at temperatures below the phase transition temperature (610 ± 5°C) by three different methods: solid-phase and microwave processes and thermolysis of a water–salt composition. According to powder X-ray diffraction, the structures of all samples belonged to space group C/2c. Depending on the method of synthesis, the particle size varied from 500 nm (thermolysis of a water–salt composition) to 5–8 μm (ceramic and microwave methods). The excitation spectra of all samples are in the UV region (220–400 nm) and the emission spectra are in the 400–750 nm wavelength range. The photoluminescence spectra of the samples are non-elementary, which is caused by specific features of the electronic charge transfer in the structural VO4 tetrahedra.

The monophase morphologically homogeneous phosphor α-Zn 2 SiO 4 :V has been produced by the hydrothermal method. With the use of energy-dispersive analysis and X-ray powder diffraction analysis, it was established that the ratio of cations Zn:Si:V corresponded to the formula Zn 2 Si 0.9 V 0.1 O 4 . The charge state of vanadium ions was determined by the spectroscopic methods. Maxima of the bands in the luminescence spectra correspond to V5+ (523 nm) and V3+ (720 nm) centers. The small width of the EPR signal hyperfine structure components indicates the presence of single V4+ centers, their contribution is not greater than 0.1% of the total vanadium content. The presence of a broad structureless component in the EPR spectrum was explained by the fact that the main amount of the dopant ion was united in the areas containing V5+, V4+ and V3+ ions. V4+ ions and V5+ ions with high probability occupy silicon positions in the lattice.

A morphologically uniform single-phase crystal phosphor α-Zn2SiO4:V was prepared by one-pot hydrothermal synthesis. Energy dispersive analysis showed that a zinc silicate-base solid solution was formed with a vanadium content of 10 ± 1 at %. Its luminescence spectrum was a broad luminescence band in the region 400–700 nm with a peak near 540 nm.

Micro- and spongiform nanocrystalline Zn 2 V 2 O 7 compounds were synthesized by hydrothermal and solid-state reaction techniques, and their morphological features were investigated by scanning electron microscopy (SEM). The grain size ranges of the produced powders were 3–15, 0.5–2 μm, and 50–500 nm. The luminescence spectra of these compounds were measured under pulse cathode beam and photoexcitation (200–400 nm). The luminescence decay properties of Zn 2 V 2 O 7 were studied. It is found that the intensity, maximum position of luminescence spectra and luminescence decay time of Zn 2 V 2 O 7 samples depend considerably on the grain size of the synthesized powders. The processes of energy relaxation in Zn 2 V 2 O 7 and the observed size effect on the luminescence properties are also discussed.

Zn2SiO4:Mn crystalline phosphor is a substitutional solid solution Zn2-2xMn2xSiO4, with х≤0.13. As the number of activator ions x > 0.13 grows, the mechanism of defect formation changes: some manganese ions change from doubly charged to triply charged, which is accompanied by the emergence of vacancies in the zinc sublattice. It is demonstrated that the coordination number of Mn3+ ions in the structure of willemite is five. The concentration quenching of Zn2SiO4:Mn is associated with the oxidation of a part of activator ions and dissipation of excitation energy on structural defects.