Evolution of Spectral and Structural Characteristics of Orthoborates Lu0.99 – xGdxEu0.01BO3

Abstract

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).

Structural and spectral characteristics of Pr-=SUB=-1-x-=/SUB=-Lu-=SUB=-x-=/SUB=-BO-=SUB=-3-=/SUB=- orthoborates

“…The following might be anticipated as a result of synthesis (at T = 970 • C) of a solid solution of LaBO 3 orthoborate, which has an aragonite structure at this temperature, and LuBO 3 which has a calcite structure at T = 970 • C: the La 1−x Lu x BO 3 compound, with an increase of the Lu 3+ (x) concentration, will have an aragonite structure first, and then a calcite phase will arise along with the aragonite structure, and the compound will have a calcite structure with a subsequent increase of x. However, as shown in [16], a different sequence of structural state alternation is observed in the La 0.98−x Lu x Eu 0.02 BO 3 compound with increase of x. With 0 ≤ x ≤ 0.1 the compounds are single-phase and have an aragonite structure.…”

“…Thus, the following conclusions can be made based on the X-ray diffraction studies. Five regions of Lu 3+ concentrations, where certain structural states exist, can be distinguished in Pr 0.99−x Lu x Eu 0.01 BO 3 orthoborates, like in La 0.98−x Lu x Eu 0.02 BO 3 compounds [16]. As lutetium concentration grows, three types of crystalline phases change successively: aragonite, vaterite and calcite (Table 2).…”

“…It was shown in [5] that the solid solution Lu 1−x In x BO 3 , consisting of lutetium borate (LuBO 3 ) having two stable structural modifications, vaterite and calcite [6][7][8], and indium borate (InBO 3 ) having only one structural modificationcalcite [9][10][11] synthesized at 780 • C (existence temperature of vaterite LuBO 3 ) with x > 0.08−0.1 crystallizes in the calcite structure. At the same time, Lu 1−x RE x BO 3 solid solutions (RE = Eu, Gd, Tb, Dy and Y), consisting of lutetium borate and REBO 3 , having only one structural modificationvaterite [6][7][8], with x > 0.15−0.2, synthesized at T = 970−1100 • C (existence temperature of calcite phase LuBO 3 ), crystallize in the vaterite structure [12][13][14][15].…”

“…An increased concentration of RE in Lu 0.99−x RE x Eu 0.01 BO 3 (RE = Gd, Eu, Tb, Y) orthoborates synthesized at 970 • C leads to a successive change of their structure: with 0 ≤ x ≤ 0.05−0.1 the solid solution of orthoborates is single-phase and has a calcite structure (space group R 3c); with 0.05−0.1 < x ≤ 0.1−0.25 a vaterite phase (space group C2/c) forms along with the calcite structure, while with x > 0.1−0.25 the solid solution is single-phase with a vaterite structure (space group C2/c) [12][13][14][15]. Morphology of orthoborate microcrystals changes simultaneously with the structure.…”

“…Papers [11][12][13][14][15] were dedicated to the study of solid solutions of lutetium borate having two structural modifications (vaterite and calcite) and borates having only one modification of lutetium borate: either calcite (InBO 3 ) or vaterite (REBO 3 , RE = Eu, Gd, Tb, Dy, Y). Paper [16] describes the structural state of the solid solution of LuBO 3 , synthesized at 970 • C, and lanthanum orthoborate (LaBO 3 ) whose structure is neither calcite nor vaterite. The LaBO 3 compound has two phase states: the low-temperature orthorhombic aragonite phase (space group Pnma) and the high-temperature monoclinic phase (space group P2 1 /m), to which LaBO 3 changes over at 1488 • C [6,17].…”