High-Pressure Stability and Compressibility of Zircon-Type YV_1–xP_xO₄:Eu³⁺ Solid-Solution Nanoparticles: An X-ray Diffraction and Raman Spectroscopy Study

Abstract

We probed the high-pressure response of the YV 1−x P x O 4 :Eu 3+ (x = 0, 0.5, 0.7, 1.0) solid-solution nanoparticles using angular dispersive synchrotron X-ray diffraction (XRD) and Raman techniques at room temperature. In situ diffraction results showed that the overall nanoparticles underwent an irreversible zircon-to-scheelite structural transformation. The transition pressures were ∼9.3, ∼12.1, ∼14, and ∼18.4 GPa for the YV 1−x P x O 4 :Eu 3+ (x = 0, 0.5, 0.7, 1.0) samples, respectively. Coupled with the zircon-toscheelite transition features, it was proposed that the transition pressure was probably governed by the stiffness of VO 4 /PO 4 units in the solid solutions. This claim was verified by further Raman measurements, which revealed that the stiffness of VO 4 /PO 4 units was enhanced with increasing P contents. The structural refinements showed that the samples with comparable particle size (20−90 nm) became less compressible with increasing P content (x = 0 → 0.7 → 1.0). However, the compressibility of the YV 0.5 P 0.5 O 4 :Eu 3+ sample with smaller particle size (10−30 nm) was similar to that of the YV 0.3 P 0.7 O 4 :Eu 3+ sample. The general compressibility behavior as a function of P content was ascribed to the special packing style related to the stiffness of VO 4 /PO 4 tetrahedra in zircon structure, and the higher surface energy contribution was responsible for the exceptional compressibility in the smaller nanoparticles. ■ INTRODUCTIONZircon-type ABO 4 ternary oxides are common accessory minerals, and they share many physical properties, as well as displaying variable degrees of solid solutions among end members existing in a wide variety of sedimentary, igneous, and metamorphic rocks. 1 The high-pressure research on zircon-type ABO 4 compounds has drawn considerable interest in the past several decades because it could provide a wide range of geochemical and geophysical investigations, including studies on the evolution of Earth's crust and mantle. 1,2 Apart from the geophysical importance, the rare-earth orthovanadates RVO 4 and orthophosphates RPO 4 currently attract considerable interest by virtue of their wide potential applications and interesting optical/luminescent properties. 3−6 They generally crystallize, depending on the ionic radii of the R cation, in two different structural types: zircon [space group (SG): I4 1 /amd, Z = 4] and monazite [SG: P2 1 /n, Z = 4]. Those with a small R size (r R < r La for RVO 4 and r R < r Gd for RPO 4 ) adopt the zircon structure under ambient conditions, whereas the others have the lower-symmetry monoclinic monazite structure. 7−9 Specifically, depending on the growth conditions, GdPO 4 , TbPO 4 , DyPO 4 , and HoPO 4 can adopt either zircon or monazite structure. 10 The high-pressure behavior of zircon-type RVO 4 and RPO 4 compounds was addressed recently. Upon compression, a direct transition to scheelite structure [SG: I4 1 /a, Z = 4] occurs in almost all the zircon-type RVO 4 compounds except CeVO 4 , which displays the complete zircon-to-monazite...

Comparative study of Y0.9Er0.1V1−xPxO4 nanophosphors with x = 0, 0.1, 0.5, 0.9 and 1 prepared by sol-gel and hydrothermal processes

“…Irrespective of the synthesis method used to obtain the samples, a clear shift of the [29]. The same trend was also found by Errandonea et al [47] in Raman investigations of powders YXO 4 composition with X = As, Cr, V, P, where a general decrease of the frequencies of the internal and external modes was observed in going from YPO 4 to YAsO 4 .…”

“…Specifically, the attention on Er 3+ :YV 1-x P x O 4 has recently increased because of their use in compacted and processed laser devices operating in the green range of the visible spectrum as well as in waveguides working in the near infrared range [21]. Different synthesis methods -including solid state reactions [22,23], co-precipitation [24,25], spray pyrolysis [26], sol-gel processes [27], hydrothermal [28][29][30] and microwaveassisted hydrothermal methods [31] have been used so far to obtain lanthanide-doped nanophosphors. Unfortunately, in most of these processes high temperature treatments, leading to an increase particle size, are required in order to obtain pure, single-phase materials M A N U S C R I P T A C C E P T E D ACCEPTED MANUSCRIPT 3 [27,29,30].…”

“…Different synthesis methods -including solid state reactions [22,23], co-precipitation [24,25], spray pyrolysis [26], sol-gel processes [27], hydrothermal [28][29][30] and microwaveassisted hydrothermal methods [31] have been used so far to obtain lanthanide-doped nanophosphors. Unfortunately, in most of these processes high temperature treatments, leading to an increase particle size, are required in order to obtain pure, single-phase materials M A N U S C R I P T A C C E P T E D ACCEPTED MANUSCRIPT 3 [27,29,30]. In recent years, however, new sol-gel processes [27] and hydrothermal synthesis procedures [28][29][30] have been successfully developed with the aim of obtaining YV 1-x P x O 4 solid solutions at low temperatures, providing non-agglomerated nanoparticles with high purity and homogeneity.…”

“…Unfortunately, in most of these processes high temperature treatments, leading to an increase particle size, are required in order to obtain pure, single-phase materials M A N U S C R I P T A C C E P T E D ACCEPTED MANUSCRIPT 3 [27,29,30]. In recent years, however, new sol-gel processes [27] and hydrothermal synthesis procedures [28][29][30] have been successfully developed with the aim of obtaining YV 1-x P x O 4 solid solutions at low temperatures, providing non-agglomerated nanoparticles with high purity and homogeneity. In general, the hydrothermal method allows to carry out reactions at lower temperatures than those used in the sol-gel process [32,33].…”

“…In general, the hydrothermal method allows to carry out reactions at lower temperatures than those used in the sol-gel process [32,33]. However, as it has been previously reported, the hydrothermal synthesis requires subsequent heating treatments in order to obtain the corresponding pure phases [28,32] or it is carried out at relatively high temperatures [29,30]. On the other hand, modifications introduced in the preparation method might lead to changes in the crystallinity and morphology of the resulting particles, which in turn directly affect the intensity of the luminescence emission bands [29,33,34].…”