The structure, IR absorption and luminescence spectra, and morphology of Lu 0.99-x Sm x Eu 0.01 BO 3 (0≤ x≤0.99) orthoborates synthesized at 970 o C were studied. With an increase in the Sm 3+ concentration, a successive change of five structural states is observed: calcite (0≤ x≤ 0.1)-> calcite + vaterite (0.1 vaterite (0.3≤ x≤ 0.95)-> vaterite + a triclinic phase (0.95 a triclinic phase (0.98

The structure, morphology, IR spectra, as well as luminescence spectra and luminescence excitation spectra of europium-doped borates formed during the interaction of lanthanum and scandium oxides with a potassium tetraborate melt at 970 o C with the general formula La 0.99-x Sc x Eu 0.01 BO 3 were studied. It is shown that with an increase in the Sc 3+ concentration, three compounds are successively formed: LaBO 3 , LaSc 3 (BO 3 ) 4 , and ScBO 3 . At 0≤ x≤ 0.26, the samples are single-phase and have the structure of LaBO 3 aragonite. Within the range of 0.26<x<0.75, the samples are two-phase and contain the structures of LaBO 3 aragonite and LaSc 3 (BO 3 ) 4 huntite. At 0.75≤ x≤0.85, LaSc 3 (BO 3 ) 4 is observed. Within the range of 0.85<x≤0.97, the samples are two-phase and consist of LaSc 3 (BO 3 ) 4 huntite and ScBO 3 calcite. At 0.97<x≤0.99, the ScBO 3 samples have a calcite structure. Correspondence between the structure and spectral characteristics of these compounds was established. Keywords: phosphors for LEDs, rare earth orthoborates, X-ray diffraction analysis, IR spectroscopy, luminescence spectra.

The structure, morphology, IR spectra, as well as luminescence spectra and luminescence excitation spectra of europium-doped borates formed during the interaction of lanthanum and scandium oxides with a potassium tetraborate melt at 970°С with the general formula La0.99-xScxEu0.01BO3 were studied. It is shown that with an increase in the Sc3+ concentration, three compounds are successively formed: LaBO3, LaSc3(BO3)4, and ScBO3. At 0 ≤ x ≤ 0.26, the samples are single-phase and have the structure of LaBO3 aragonite. Within the range of 0.26 < x < 0.75, the samples are two-phase and contain the structures of LaBO3 aragonite and LaSc3(BO3)4 huntite. At 0.75 ≤ x ≤ 0.85, LaSc3(BO3)4 is observed. Within the range of 0.85 < x ≤ 0.97, the samples are two-phase and consist of LaSc3(BO3)4 huntite and ScBO3 calcite. At 0.97 < x ≤ 0.99, the ScBO3 samples have a calcite structure. Correspondence between the structure and spectral characteristics of these compounds was established.

The structure, IR absorption and luminescence spectra, and morphology of Lu0.99xSmxEu0.01BO3 (0 ≤ x ≤ 0.99) orthoborates synthesized at 970°С were studied. With an increase in the Sm3+ concentration, a successive change of five structural states is observed: calcite (0 ≤ x ≤ 0.1) → calcite + vaterite (0.1 < x < 0.3) → vaterite (0.3 ≤ x ≤ 0.95) → vaterite + a triclinic phase (0.95 < x ≤ 0.98) → a triclinic phase (0.98 < x ≤ 1). A wide range of Sm3+ concentrations at which the vaterite phase (0.3 ≤ x ≤ 0.95) exists and a very narrow region of triclinic phase formation (0.98 < x ≤ 1) are important distinctive features of this system. Correspondence between the structure and spectral characteristics of these compounds was established. It is shown that the vaterite phase appears in the bulk of the microcrystals of the samples that have a calcite structure.

The structure, IR, luminescence, and luminescence excitation spectra of Ce3+, Tb3+, and Eu3+ ions in Lu1-2xCexEuxBO3 and Lu0.91-2xCexTb0.09EuxBO3 solid solutions were studied. The minimum "threshold" distance between Ce3+ and Eu3+ ions was estimated, at which there is no charge transfer between these ions, leading to the quenching of Ce3+ and Eu3+ luminescence. It is shown that in Lu0.91-2xCexTb0.09EuxBO3 compounds, the range of Ce and Eu concentrations of 0.2-0.25 at.% is optimal for obtaining the maximum luminous intensity of this compound. Keywords: phosphors for LEDs, rare earth orthoborates, X-ray diffraction analysis, IR spectroscopy, luminescence spectra.

The structure, IR absorption, luminescence, and luminescence excitation spectra of La 0.99-x Y x Eu 0.01 BO 3 orthoborates synthesized at 970 o C were studied at 0≤ x≤0.99. An increase in x leads to a sequential change of the structural state of these compounds. At 0≤ x≤0.1, the samples are single-phase and have the aragonite structure. Within the range of 0.1^7F 0 electron transition, as well as 469 nm-band in the LES, can be an indicator of the structural state of the sample. Keywords: rare earth orthoborates, X-ray diffraction analysis, crystal structure, IR spectroscopy, luminescence spectra.

The structure, infrared (IR) absorption spectra, luminescence spectra (SL), and luminescence excitation spectra (LES) of La 0.99-x Tb x Eu 0.01 BO 3 orthoborates synthesized at 970 o C at 0≤ x≤ 0.99 were studied. An increase in x leads to the successive emergence of three structural states of these compounds. At 0≤ x≤0.2, orthoborates have an aragonite structure; then, at 0.2 5 D 2 ) in the LES and the band in the wavelength range of 577-582 nm ( 5 D 0 -> 7 F 0 ) in the SL of these compounds can serve as indicators of the structural state of the sample. In the SL of the samples containing the aragonite and vaterite phases, two bands corresponding to these structures were simultaneously observed for the first time. It was established that the luminescence of Eu 3+ ions in La 0.99-x Tb x Eu 0.01 BO 3 orthoborates, which occurs when the sample is excited by light in the absorption bands of Tb 3+ ions, is due to the transfer of the electron excitation energy from Tb 3+ ions to Eu 3+ ions. The efficiency of this process in La 0.9 Tb 0.09 Eu 0.01 BO 3 samples with an aragonite structure is 86%. Keywords: rare earth orthoborates, crystal structure, X-ray diffraction analysis, IR spectroscopy, luminescence spectra, phosphors for LEDs.

The structure, IR absorption and luminescence spectra of Pr0.99xLuxEu0.01BO3 orthoborates synthesized at 970°C were studied at 0 ≤ x ≤ 0.99. An increase in the concentration of lutetium leads to a sequential change of the structural state of the orthoborates. At first, the orthoborates are single-phase and have an aragonite structure (0 ≤ x ≤ 0.1). Then, they become two-phase and contain the aragonite and vaterite phases (0.1 < x < 0.6). With a further increase in х (0.6 < x ≤ 0.8), the compounds are single-phase with a vaterite structure, then they contain the vaterite and calcite phases (0.8 < x ≤ 0.95), and, finally, they become single-phase with a calcite structure (0.95 < x ≤ 0.99). An unambiguous correspondence between the structural modification and IR spectra of these compounds was established. It is shown that the emission of Eu3 + ions is observed in samples where the concentration of europium exceeds that of praseodymium.

The structure, IR absorption and luminescence spectra of Pr 0.99-x Lu x Eu 0.01 BO 3 orthoborates synthesized at 970 o C were studied at 0≤ x≤0.99. An increase in the concentration of lutetium leads to a sequential change of the structural state of the orthoborates. At first, the orthoborates are single-phase and have an aragonite structure (0≤ x≤0.1). Then, they become two-phase and contain the aragonite and vaterite phases (0.1<x<0.6). With a further increase in x (0.6<x≤0.8), the compounds are single-phase with a vaterite structure, then they contain the vaterite and calcite phases (0.8<x≤0.95), and, finally, they become single-phase with a calcite structure (0.95<x≤0.99). An unambiguous correspondence between the structural modification and IR spectra of these compounds was established. It is shown that the emission of Eu 3+ ions is observed in samples where the concentration of europium exceeds that of praseodymium. Keywords: rare earth orthoborates, X-ray diffraction analysis, crystal structure, IR spectroscopy, luminescence spectra.

The structure, IR absorption spectra, luminescence spectra (SL), and luminescence excitation spectra (LES) of La0.99хTbxEu0.01BO3 orthoborates synthesized at 970°С at 0 ≤ x ≤ 0.99 were studied. An increase in x leads to the successive emergence of three structural states of these compounds. At 0 ≤ x ≤ 0.2, orthoborates have an aragonite structure; then, at 0.2 <x< 0.89, they become two-phase and contain the aragonite and vaterite phases. At 0.89 ≤ x ≤0.99, the compounds have a vaterite structure. A correspondence between the structure and spectral characteristics of these compounds was established. It is shown that in La0.99хTbxEu0.01BO3 orthoborates, as well as in La0.99хYxEu0.01BO3, the band with λex= 369 nm (7F0 → 5D2) in the LES and the band in the wavelength range of 577 – 582 nm (5D0→7F0 ) in the SL of these compounds can serve as indicators of the structural state of the sample. In the SL of the samples containing the aragonite and vaterite phases, two bands corresponding to these structures were simultaneously observed for the first time. It was established that the luminescence of Eu3+ ions in La0.99хTbxEu0.01BO3 orthoborates, which occurs when the sample is excited by light in the absorption bands of Tb3+ ions, is due to the transfer of the electron excitation energy from Tb3+ ions to Eu3+ ions. The efficiency of this process in La0.9Tb0.09Eu0.01BO3 samples with an aragonite structure is 86%.

The structure, IR absorption, luminescence, and luminescence excitation spectra of La0.99xYxEu0.01BO3 orthoborates (0 ≤ x ≤ 0.25) synthesized at 970°С were studied at 0 ≤ x ≤ 0.99. An increase in х leads to a sequential change of the structural state of these compounds. At 0 ≤ x ≤ 0.1, the samples are single-phase and have the aragonite structure. Within the range of 0.1 < x ≤ 0.8, the samples are two-phase: the vaterite phase is observed along with the aragonite structure. At 0.8 < x ≤ 0.99, the samples are single-phase and have the vaterite structure. Correspondence between the structure and spectral characteristics of these compounds was established. It is demonstrated that with an increase in the Y3+ concentration, the vaterite phase is formed first in the bulk of microcrystals having the aragonite structure and then in the entire sample. It is shown for the first time that a band with the maximum of 469 nm is observed in the luminescence excitation spectrum (LES) of samples having the vaterite structure and is absent in samples having the aragonite structure. It is revealed that a band in the luminescence spectrum, corresponding to the 5D0→7F0 electron transition, as well as 469-nm-band in the LES, can be an indicator of the structural state of the sample.

The structure, IR, luminescence, and luminescence excitation spectra of Ce3+, Tb3+, and Eu3+ ions in Lu1−2xCexEuхBO3 and Lu0.91−2xCexTb0.09EuхBO3 solid solutions were studied. The minimum "threshold" distance between Ce3+ and Eu3+ ions was estimated, at which there is no charge transfer between these ions, leading to the quenching of Ce3+ and Eu3+ luminescence. It is shown that in Lu0.91−2xCexTb0.09EuхBO3 compounds, the range of Ce and Eu concentrations of 0.2 – 0.25 at. % is optimal for obtaining the maximum luminous intensity of this compound.

The structure, IR absorption, luminescence, and luminescence excitation spectra of La 0.98-x Lu x Eu 0.02 BO 3 orthoborates synthesized at 970 o C were studied at 0≤ x≤0.98. An increase in x leads to a sequential change of the structural state of the orthoborates. At first, the compound has the aragonite structure. Then, it becomes two-phase and contains the aragonite and vaterite phases. With a further increase in x, the compounds have the vaterite structure, then the vaterite and calcite structure, and, finally, the calcite structure. Correspondence between the structure and spectral characteristics of these compounds was established. Luminescence spectra were investigated at different wavelengths of exciting light. This allowed obtaining information on the structure of a near-surface layer and the bulk of microcrystals of the investigated samples. It is shown that the vaterite phase arises in the bulk of microcrystals of samples that have the aragonite structure. Keywords: phosphors for LEDs, rare earth orthoborates, X-ray diffraction analysis, IR spectroscopy, luminescence spectra.

The structure, IR absorption and luminescence spectra of solid solutions of Lu0.99 ‒ xGdxEu0.01BO3 at 0 ≤ x ≤ 0.15 were studied. The correspondence between the structure and spectral characteristics of these compounds was established. It is shown that at x ≤ 0.05, the orthoborates Lu0.99 ‒ xGdxEu0.01BO3, consisting of lutetium borate LuBO3, which has two stable structural modifications (calcite and vaterite), and gadolinium borate GdBO3, which has only one structural modification (vaterite), form a solid solution with a calcite structure and a microcrystal size of 15–20 μm. As x increases, the amount of vaterite phase increases sequentially, and at x ≥ 0.1, the entire volume of the sample has a vaterite structure. At Gd3+ concentration in the range of 0.05 < x ≤ 0.1, the samples of Lu0.99 – xGdxEu0.01BO3 are two-phase. It is shown for the first time that at x > 0.05, the vaterite phase appears both in the volume of large microcrystals (15–20 μm) and in the form of small microcrystals (1–2 μm).

The structure, IR absorption, luminescence, and luminescence excitation spectra of La0.98xLuxEu0.02 BO3 orthoborates synthesized at 970°C were studied at 0 ≤ x ≤ 0.98. An increase in х leads to a sequential change of the structural state of the orthoborates. At first, the compound has the aragonite structure. Then, it becomes two-phase and contains the aragonite and vaterite phases. With a further increase in х, the compounds have the vaterite structure, then the vaterite and calcite structure, and, finally, the calcite structure. Correspondence between the structure and spectral characteristics of these compounds was established. Luminescence spectra were investigated at different wavelengths of exciting light. This allowed obtaining information on the structure of a near-surface layer and the bulk of microcrystals of the investigated samples. It is shown that the vaterite phase arises in the bulk of microcrystals of samples that have the aragonite structure.

The structure, IR absorption and luminescence spectra of solid solutions of Lu 0.99 ‒ x Gd x Eu 0.01 BO 3 at 0 ≤ x ≤ 0.15 were studied. The correspondence between the structure and spectral characteristics of these compounds was established. It is shown that at x ≤ 0.05, the orthoborates Lu 0.99 ‒ x Gd x Eu 0.01 BO 3 , consisting of lutetium borate LuBO 3 , which has two stable structural modifications (calcite and vaterite), and gadolinium borate GdBO 3 , which has only one structural modification (vaterite), form a solid solution with a calcite structure and a microcrystal size of 15–20 μm. As x increases, the amount of vaterite phase increases sequentially, and at x ≥ 0.1, the entire volume of the sample has a vaterite structure. At Gd 3+ concentration in the range of 0.05 < x ≤ 0.1, the samples of Lu 0.99 – x Gd x Eu 0.01 BO 3 are two-phase. It is shown for the first time that at x > 0.05, the vaterite phase appears both in the volume of large microcrystals (15–20 μm) and in the form of small microcrystals (1–2 μm).

The structure, IR absorption spectra, and luminescence spectra of orthoborates Lu0.98 ‒ xInxEu0.02BO3 at 0 ≤ x ≤ 0.1 has been studied. It is shown that a Lu1 – xInxBO3 solid solution consisting of lutetium borate LuBO3, which has two stable structural modifications (calcite and vaterite), and indium orthoborate InBO3, which has only one structural modification (calcite), is crystallized almost completely into the calcite st-ructure at x = 0.1. It is shown for the first time that structural transformations in orthoborates Lu0.98 ‒ xInxEu0.02BO3 with an increase in the In3+ ion concentration begin in the surface layer of microcrystals of these compounds. The amount of the calcite phase successively increases with an increase in x in the sample bulk as well; for the Lu0.88In0.1Eu0.02BO3 composition, 98% of the sample volume is comprised of the calcite structure.

The structure, the IR absorption spectra, and the luminescence spectra of microcrystals of orthoborates Lu1 – xEuxBO3, Lu0.99 – xTbxEu0.01BO3, and Lu0.99 – xYxEu0.01BO3 with 0 < x < 0.25 synthesized at 970°C have been studied. An increase in x leads to a sequential change in the structural state of the orthoborates. At x ≤ 0.07–0.1, the compounds form the solid solution with the calcite structure and the microcrystal sizes 8–20 μm, then they become two-phase: the vaterite phase appears along with the calcite structure. At x ≥ 0.2–0.25, a whole sample volume has the vaterite structure. It is found that there is correlation between the structure and the spectral characteristics of these compounds. The luminescence spectra are studied at various wavelengths of the exciting light, which allowed the obtainment of the information on the structure of the near- surface layer and the bulk of microcrystals of these samples. The vaterite phase is shown to form both in the coarse microcrystal bulks (8–20 μm), and as fine microcrystals (1–2 μm).

The structure, IR absorption and luminescence spectra of the microcrystals of Lu1-xEuxBO3, Lu0.99-xTbxEu0.01BO3, and Lu0.99−xYxEu0.01BO3 orthoborates (0 ≤ x ≤ 0.25) synthesized at 970°С were studied. An increase in х leads to a sequential change of the structural state of the orthoborates. At х ≤ 0.07 – 0.09, the compounds form a solid solution with the calcite structure and microcrystal size of 8 – 20 µm. Then, they become two-phase: the vaterite phase arises along with the calcite structure. At х ≥ 0.2 – 0.25, the entire bulk of a sample has the vaterite structure. A correspondence between the structure and spectral characteristics of these compounds was established. Luminescence spectra were investigated at different wavelengths of exciting light. This allowed obtaining information on the structure of a near-surface layer and the bulk of microcrystals of the investigated samples. It is shown that the vaterite phase arises both in the bulk of large microsrystals (8 – 20 µm) and in the form of small microsrystals (1 – 2 µm).

The structure and the IR absorption and luminescence spectra of the Lu0.98-хInхEu0.02BO3 orthoborates are studied at 0 ≤ x ≤ 0.1. The Lu1-xInxBO3 solid solution, which consists of lutetium borate LuBO3 having two stable structural modifications (calcite, vaterite) and indium orthoborate InBO3 having one structural modification (calcite), crystallizes at x = 0.1 to form a calcite structure almost throughout the volume. We showed that the structural transformations in the Lu0.98-хInхEu0.02BO3 orthoborates induced by an increase in the In3+ ion concentration begin in the near-surface layers of the orthoborate microcrystals. The amount of calcite increases in the sample volume with x, and calcite occupies 98% of the Lu0.88In0.1Eu0.02BO3 sample volume.