Photoluminescence and Raman Spectroscopy Studies of Eu(OH)₃ Rods at High Pressures

Abstract

Eu(OH)3 rods, with diameters of 140 nm and lengths of 100−500 nm were prepared by a hydrothermal method. X-ray diffraction indicated a pure hexagonal phase (space group P63/m) of the rods. The relations between structural and optical properties of Eu(OH)3 rods under high pressures were obtained by photoluminescence (PL) and Raman spectra. Two structural phase-transition points at around 4 and 8 GPa were observed in this work. When a pressure of about 4 GPa was applied to the samples, one new emission peak at 593 nm was observed in the PL spectra, indicating the splitting of the 7F1 Stark level in Eu3+ ions. Such a splitting was attributed to the decrease of site symmetry of Eu3+ ions from C 3h to D 2 at high pressures. Two new Raman bands appeared under a pressure up to about 8 GPa due to the pressure-induced amorphization. After the pressure was released, the original PL and Raman spectra were recovered.

Pressure-induced structural evolution and amorphization in Eu3Ga5O12

“…7 F 1 is usually used to describe the degree of asymmetry in the vicinity of Eu 3þ , and can thus provide valuable information about changes of the local structure around Eu 3þ . [39][40][41][42] As shown in Fig. 7, the intensity ratio I (J¼2/J¼1) decreases with increasing pressure up to 5 GPa, and can be associated with an increase in the average Eu-O bond distance or a decrease in the covalency of the Eu-O bond.…”

Well-defined crystallites autoclaved from the nitrate/NH4OH reaction system as the precursor for (Y,Eu)2O3 red phosphor: Crystallization mechanism, phase and morphology control, and luminescent property

“…5(c)) similar to that of the LRH phase in a low hydration state (Ln 2 (OH) 5 NO 3 Á 1.06H 2 O) [41], which may imply that they have similar local environments of Eu 3 þ . The (Y 0.95 Eu 0.05 )(OH) 3 phase is hexagonal in structure and consists of 9-coordinated Eu 3 þ ions in D 3h symmetry [49]. The centrosymmetric high site symmetry thus causes weaker 5 D 0 -7 F 2 (at 615 nm) than 5 D 0 -7 F 1 (at 595 nm) transitions and also the absence of the 5 D 0 -7 F 0 one (Fig.…”

“…2(e)). Structurally, Y(OH) 3 is a trigonal prism with the 9-coordinated Y 3 þ located in the center of the prism [48,49]. Six of the nine coordinating oxygen atoms locate at each of the corners of the trigonal prism: three above the midhorizontal plane and three below [48,49].…”

“…Structurally, Y(OH) 3 is a trigonal prism with the 9-coordinated Y 3 þ located in the center of the prism [48,49]. Six of the nine coordinating oxygen atoms locate at each of the corners of the trigonal prism: three above the midhorizontal plane and three below [48,49]. The other three coordinating oxygen atoms are equatorial, with each of them located on a normal to a rectangular face of the trigonal prism [48,49].…”

“…Six of the nine coordinating oxygen atoms locate at each of the corners of the trigonal prism: three above the midhorizontal plane and three below [48,49]. The other three coordinating oxygen atoms are equatorial, with each of them located on a normal to a rectangular face of the trigonal prism [48,49]. The Y atomic array can be viewed as infinite linear chains in this structure model [48], and is believed to be responsible for the development of the rod-like morphology observed in Fig.…”