Structural study and spectroscopic properties of NH4Er(PO3)4

Accepted Manuscript Structural study and spectroscopic properties of NH4Er(PO3)4 Jalila Chékir-Mzali, Karima Horchani-Naifer, Mokhtar Férid PII: DOI: Reference:

S0925-8388(14)01320-6 http://dx.doi.org/10.1016/j.jallcom.2014.05.213 JALCOM 31402

To appear in: Received Date: Revised Date: Accepted Date:

4 February 2014 29 May 2014 29 May 2014

Please cite this article as: J. Chékir-Mzali, K. Horchani-Naifer, M. Férid, Structural study and spectroscopic properties of NH4Er(PO3)4, (2014), doi: http://dx.doi.org/10.1016/j.jallcom.2014.05.213

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Structural study and spectroscopic properties of NH4Er(PO3)4

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Jalila Chékir-Mzali*, Karima Horchani-Naifer and Mokhtar Férid

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Laboratory of Physical Chemistry of Mineral Materials and their Applications, National

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Research Center in Materials Sciences, Technopole Borj Cedria B.P. 73- 8027 Soliman,

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Tunisia.

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Corresponding author: jalila Chékir-Mzali E-mail: [email protected]

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Tèl. : +216 --- 7932--- 5470

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Abstract

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Single crystals of NH4Er(PO3)4 polyphosphate have been prepared by the flux method

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and its structural and physical properties have been investigated. This compound crystallizes

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in the monoclinic system, with space group P21/n and the following parameters:

13

10.259(3) Å, b = 8.884(3) Å, c = 10.910(3) Å, β = 106.27(1)°, V = 954.5(5) Å3 and Z = 4. Its

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structure is characterized by PO4 phosphate groups which are assembled through common

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vertices to form (PO3)n spiral chains running along the [101] direction. These chains are

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linked to each other by ErO8 polyhedra through common corners. In such a way the resulting

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3D framework forms large tunnels, parallel to the [100] direction, where the NH4 + ions are

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located. Raman and FT-IR spectra have been registered and discussed. Absorption, excitation

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and emission spectra of NH4Er(PO3)4 have been investigated for the first time: they show

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bands characteristics of the Er3+ ions. Decay curves for 2H11/2, 4S3/2 and 4F9/2 levels of Er3+ ion

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have also been studied.

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Keywords: Rare earths; Polyphosphate; X-ray diffraction; Vibrational spectroscopy;

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Spectroscopic property.

a =

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1. Introduction

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Presently, Rare earth doped materials attract much attention due to their practical importance

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in many fields such as novel three-dimensional solid-state displays and biomedical multi-

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color imaging [1], lasers materials [2]. Particularly, the Er3+ attracts the attention of scientists

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due to their infrared spectral emission around 1530 nm through the 4I13/2 → 4I15/2 transition

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which exhibit extensive applications used in wavelength-division-multiplexing (WDM)

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network applications [3], laser applications [4] and waveguide amplifier applications [5].

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Due to their rich energy level structure, the spectroscopy of the trivalent erbium in the

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ultraviolet, visible and infrared (IR) wavelength range, is studied in many matrices such as

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glasses [6] and [7], oxides [8], silicates [9], phosphates [10].

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Moreover some of them present interesting optical properties due to the relatively

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large Ln-Ln distances [11-12]. In addition, they show a high stability under normal conditions

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of temperature humidity, and perfect crystallinity. Besides, they are not water soluble as may

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be inferred from their estimated molecular weights and they all produce glasses when heated

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to their melting points. Due to these interesting reasons, many works have been devoted to the

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study of alkali rare earths polyphosphates. For example, LiMІІІ(PO3)4 (MІІІ = Y, Er [13], La

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[14], Tb [15], Pr [16], Sm [17], Gd [18], Yb [19], Nd [20], Mn [21] and NH4MІІІ(PO3)4 (MІІІ

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= Er [22], Bi [23], Ce [24] have been reported recently. They crystallize in the monoclinic

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system with C2/c space group for LiYb(PO3)4 and LiEr(PO3)4 compounds. Their structure

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consist of 3D frameworks made up of spiral (PO3)n chains linked by MIIIO8 polyhedra and the

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Li atoms are tetra-coortinated [19]. NH4Bi(PO3)4 and NH4Ce(PO3)4 crystallize in the non-

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conventional space group P21/n [23, 24]. In the cerium phosphate, the rare earth atoms are

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eight coordinated while the NH4 groups have nine oxygen neighbors. Infinite (PO3)n chains

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with a period of eight tetrahedral spread along the [101] direction.

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NH4Er(PO3)4 (type: IV) is a member of the MІMІІІ(PO3)4 family. It has been previously

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synthesized as powder by thermal method [22]. In this paper, we report its chemical

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preparation as single crystals and its crystal structure. Its characterization by IR and Raman

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and its photoluminescence study are also reported.

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2. Experimental

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2.1. Synthesis

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Single crystals of NH4Er(PO3)4 have been synthesized by the flux method starting

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from a mixture of 3g of (NH4)2 HPO4 and 0.4 g of erbium oxide Er2O3 which were slowly

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added to 13 ml of phosphoric acid H3PO4 (85%). This mixture was homogenized, transferred

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into a vitreous carbon crucible, and placed in a muffle furnace for 3h at 473 K and

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subsequently heated to 623K and kept at this temperature during 7 days before switching off

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the furnace. After few hours of decreasing temperature, purple and parallelepiped crystals

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were obtained by washing the product in boiling water to remove the excess of phosphoric

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acid.

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2.2. Measurements

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All measurements were recorded at RT. The X-ray data were collected on a crystal of

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dimensions 0.20 mm × 0.18 mm × 0.16 mm, by an Enraf-Nonius CAD4 diffractometer using

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Mo-Kα radiation (λ = 0.71073 Å). A total of 3550 unique reflections was measured using the

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w/2θ scan type for 2θmax = 33.06 but only 3356 reflections were considered as observed

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according to the statistic criterion [I >2σ (I)]. The systematic absence of k =2n+1 for 0 k 0

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and h = 2n+1 for h 0 l indicated the monoclinic space group P21/n. The intensity data were

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corrected for Lorentz and polarization effects. The structure solution was performed by

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SHELXS97 [25], and subsequently refined by SHELXL97 [26]. These two programs are

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included in the basis of WINGX [27]. The positions of the erbium atoms were obtained using

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the Patterson heavy atom method. Successive Fourier analysis allowed the localization of the

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remaining atoms. A last cycle of refinement, including anisotropic thermal parameters for all

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non hydrogen atoms, led to the reliability factors R1 = 0.0308 and wR2= 0.0923. The

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crystallographic data and recording conditions are reported in Table 1. The coordinates of

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atoms, inter-atomic distances and bond angles are reported in Tables 2, and 3 respectively.

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The graphic structure was created by DIAMOND program [28].

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The IR spectrum of the synthesized sample was recorded by a Perkin Elmer

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(FTIR2000) spectrometer in the range of 4000−400 cm-1 using KBr pellets. The Raman and

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PL spectra were recorded using HORIBA Scientific (labRAM HR) spectrometer equipped

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with Laser source (632 nm and 325nm) and CCD detector. Absorbance spectrum was

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registered on a sintered pellet of polycrystalline powders in a wavelength range of 250–

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1800nm, using a double-beam Lambda 950 Series UV/Vis & UV/Vis/NIR Perkin-Elmer

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Spectrophotometer with a diffuse reflectance accessory integrating sphere. The IR

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photoluminescence measurement was performed under 488nm line of an argon ion Ar + laser

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as excitation source. The excitation spectrum and delay time curves were registered by a Perkin-

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Elmer spectrophotometer (LS 55) with Xenon lamp (200-700 nm).

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3. Results and discussion

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3.1. Description of the structure

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NH4Er(PO3)4 crystallizes in the monoclinic system with space group P21/n. The

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asymmetric unit (Table 2) contains 22 atomic positions including one for N, four for H, one

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for Er, four for P and twelve for O. All these atoms occupy general positions.

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The structure as projected along the [100] direction is viewed in Figure 1 showing the

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great complexity of the [Er(PO3)4]-∝ anionic framework, consisted by (PO3)n infinite spiral

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units, made of corner-sharing PO4 tetrahedra. Such units are arranged parallel to the

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crystallographic b-direction, around the 2 1 helicoidal axis (Fig. 2). Their connection is ensured

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by the ErO8 polyhedra through Er–O–P links. This structure can be considered as an ordered

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defect variant of threefold supercell of monazite [MIIIPO4] [29].

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It is worth pointing out that, despite their different crystal structures, the

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NH4Ln(PO3)4 (Ln = Er (this work), Ce [24], Bi [23], Gd [30]) ammonium rare earth

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phosphates are all exhibiting three-dimensional frameworks which form large tunnels where

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the NH4 + groups are located. These tunnels, which are parallel to the [101] direction, are

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formed by infinite screw (PO3)∝ chains joined to each other by LnO8 polyahedra.

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3.1.1 Anionic groups

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The bond distances and angles in NH4Er(PO3)4 are given in Table 3. All phosphorus

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atoms are tetrahedrally coordinated forming phosphate tetrahedra. Each tetrahedron is

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connected by two common corners in cis position to two other tetrahedra giving rise to a

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twisted (PO3)n- chain.

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The P-O distances in the PO4 tetrahedra (Table3) can be divided into two groups:

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linking distances (P–O)(Lij), that range from 1.566(4) to 1.592(5) (Å), and exterior distances

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(P–O)(Eij) ranging from 1.448(4) to 1.474(4) (Å), where O(Lij ) denotes the O atom that links

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Pi with Pj and O(Eij ) corresponds to the jth in O atom exterior to the chain and bonded to

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phosphorus Pi (Fig. 3). The O-P-O angles vary from 97.3(8)° to 121.1(1)°. The calculation of

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the distortion indices (ID) for the O–P–O angles and the O–O and P–O distances [DI (O–P–

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O), DI (O–O) and DI (P–O), respectively] (Table 4) according to the Baur method [31]

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shows the relative deformation of all the PO4 tetrahedra.

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3.1.2 Er3+ and NH4+ environments

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In the titled structure, the erbium and ammonium atoms are located between (PO3)4-

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chains to ensure the cohesion and the neutrality of the structure. The ErO8 polyhedra are

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isolated from each other. The Er-O distances range from 2.333(1) to 2.475(8) (Å) (Table 3).

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Corresponding mean distance = 2.406(5) Å is somewhat higher than those observed in

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other Erbium phosphates [32], showing that the Er–O bonds are weakened due to the highly

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covalent character of the antagonist P–O bonds, as determined for both NH4+ and H2PO4−

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groups of the NH4H2PO4 compound during the crystallization of ADP crystals [33, 34].

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According to Errandonea et al. [35], the bulk modulus can be estimated from Er-

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O average distance = d by the equation B0 = 610 * Z / d^3, where B0 is the bulk modulus

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in GPa and Z the formal charge of Er = 3. The calculation leads to B0 = 130 GPa.

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The shortest distance between erbium atoms is Er…Er = 5.695 Å. Its comparison with

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other related compound shows that the evolution of this distance is consistent with the radii of

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the Ln3+ ion. In fact, the Er…Er distance is slightly higher than the shortest Y…Y distance of

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5.687(Å) observed in NH4Y(PO3)4 [36] but lower than that of 5.739 (Å) reported for Gd…Gd

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distance in NH4Gd(PO3)4 [30]. This evolution is consistent with the fact that r(Gd3+) > r(Er3+)

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> r(Y3+).

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The NH4+ cationic group is coordinated by eight oxygen atoms with N−O distances

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ranging from 2.911 (Å) to 3.326 (Å) (Fig. 1). Similar coordination for ammonium has already

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been observed in NH4Y(PO3)4 [36]. We note that the NH4 tetrahedron is slightly distorted as

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N−H−N angles shows 81.9(6) to 141.3(6) °. The positions of the hydrogen atoms attached to

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nitrogen were determined from a difference Fourier map and were refined isotropically.

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3.1.3 Bond valence analysis

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The bond valence sums (BVS) for the erbium and phosphors atoms were calculated by

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the Brown and Alttermat method [37] using the cation-oxygen distances obtained by X-ray

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diffraction. The obtained values for P (Table 5) range from 5.039 to 5.149 with an average

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value of 5.084, close to the ideal value of 5. The BVS calculated for Erbium (2.776), for

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oxygen (-1.919) are in accordance with their formal charges of +3 and -2, respectively.

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3.2. Vibrational characterization of NH4Er(PO3)4

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The IR and Raman spectra for NH4Er(PO3)4 are shown in Figures 4 and 5,

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respectively. The frequencies for the corresponding bands are given in Table 6. The observed

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bands clearly indicate the existence of infinite chains of PO4 tetrahedra bound by bridging

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oxygen [38]. Moreover, the IR absorption spectrum is characterized by the appearance of an

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intense and strong band around 3275 cm-1, attributed to ν(N-H). The band observed around

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1437 cm-1 correspond to δ(NH4+). Our results are in accordance with those reported in recent

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results studies about the compounds of NH4 H2PO4 and KH2PO4 by using in situ ATR-IR

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spectroscopy [33, 39, 40]. Similar assignments were also reported for NH4Ce(PO3)4 [24].

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The strong band around 1252 cm-1 which is assigned to the asymmetric vibration νas(PO2)-

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corresponds to the few lines in the Raman spectrum that appear in the 1400-1200cm-1 region.

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The average bands observed at 1167 and 1084 cm-1 in the IR spectrum and the broad line at

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1186 cm-1 in the Raman spectrum can be assigned to the symmetric vibration of νs(PO2)-.

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Also, we attribute the two bands between 812 and 780 cm-1 in the IR spectra and the few lines

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occurring at 1151 and 974 cm-1 in the Raman spectrum to the asymmetric vibration of νas(P-

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O-P). Symmetric stretching vibrations νs(P-O-P) in chain polyphosphate occur by large bands

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located in the 810-619 cm-1area in IR spectrum and intense lines at 744 cm-1 in the Raman

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spectrum. It is worth pointing out that it is very difficult to distinguish between the symmetric

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deformation (δs) and the asymmetric deformation (δas) bending modes of (PO2)- species and

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δ(POP) bending, located in the low frequency region below 621 cm-1, Moreover, these modes

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often overlay with external modes. A comparison of the IR bands and Raman lines of the

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titled compound shows that the majority of them do not coincide, which is in agreement with

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the centrosymmetry of the NH4Er(PO3)4 structure.

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3.3. Luminescence properties

3.3.1. Absorption spectrum

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Absorption spectrum of NH4Er(PO3)4 is presented in Fig. 6. This spectrum shows 10

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bands peaked at 350, 387, 429, 470, 505, 527, 635, 777, 978 and 1515 nm corresponding to

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the absorption transitions from the ground state 4I15/2 to the excited states 4G11/2, 4F3/2, 4F5/2,

173

4

F7/2, 2H11/2, 4S3/2, 4F9/2, 4I9/2, 4I11/2 and 4I13/2 respectively [41, 42]. In order to determine the

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band gap energy, we used the Tauc plot method [43]: (αhν)2 = ( hν – Eg); where hν is the

175

photon energy (eV). The optical band gap was estimated by extrapolating the straight line

176

portion of the (αhν)2 versus photon energy E = hν plot until null absorption what leads to the

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determination of the gap of 4.169 eV ( Fig. 7). 3.3.2 Emission spectrum

178 179

The emission spectrum is presented in Fig. 8(a). It shows the characteristic emission

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lines resulting from the intra-configurational electronic from different excitations levels to

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4

I15/2 fundamental level in the range of 350 to 700 nm under excitation at 325 nm (≈ 30769

182

cm-1). The origin of all emission lines observed in the spectrum (Fig. 8(b)) is indeed the result

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of the re-absorption of the laser light by the erbium ions incorporated in the entitled matrix,

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which is in accordance with the work of Eric Tanguy [44]. In order to identify different

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groups of lines, we have referred to Hangjun Wu et al. [45]: two green emissions lines that

186

are located around 523 nm (≈ 19120 cm-1) corresponding to (2H11/2 → 4I15/2) transition and at

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541nm (≈ 18480 cm-1) corresponding to (4S3/2 → 4I15/2) transition, one red emission line which

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is situated around 652 nm (≈ 15334 cm-1) undoubtedly corresponding to (4F9/2 →4I15/2)

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transition and all emissions lines of 4G9/2, 4G11/2, 2H9/2, 4F3/2, 4F5/2, 4F7/2 are situated

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respectively at 364 nm (≈ 27470 cm-1), 378 nm (≈ 26455 cm-1), 404 nm (≈ 24752 cm-1), 442

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nm (≈ 22624 cm-1), 449 nm (≈ 22270 cm-1) and 487 nm (≈ 20530 cm-1). The emission

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spectrum upon 488nm wavelength excitation, registered between 1400 and 1700 nm is shown

193

in figure 8(b). It presents the characteristic emission band observed at 1535 nm (≈ 6666 cm-1)

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[46], assigned to the security ocular and undoubtedly originating to (4I13/2 → 4I15/2) transition.

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3.3.3 Excitation spectrum

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The photoluminescence excitation spectrum of the Er

3+

in NH4Er(PO3)4 is shown in Figure

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9. It was measured upon the emission wavelength λ = 657 nm. The broad excitation band that

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appears at the beginning of the spectrum (more precisely in the UV range) is identified as due

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to the charge transfer (CT) transitions of ligand O2- atoms and 4f–4f transitions within Er3+

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4f11 electron configuration. In Reference, the O2- →RE3+ CTB (RE3+ = Rare earths trivalent

201

cation) were located in the range of 200–300 nm in most phosphates [47]. In fact, this is due

202

to the strong binding of the oxygen ligands in the polyphosphate compound. Our results show

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a reasonable accordance with other compounds [48]; additionally it indicates that the

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interactions between Er3+ ions and host lattice are strong. Along this band, it is also possible

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to observe several narrow bands situated between 360 and 550 nm which are assigned to the

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appropriate electronic transitions of Er(III) ion. The attributions to these bands are reported in

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Table 7. This assignment was based on data from the literature concerning the Er3+ excitation

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in phosphate host lattices. The intensities of all emission lines should gauge of the quality for

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atoms occupation in the titled structure [46].

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3.3.4 Decay curve (2H11/2, 4S3/2 and 4F9/2)

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Figure 10 shows the decay curves for three emission under UV-excitation wavelength

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of NH4Er(PO3)4. The decays are shown to be exponential. The values of τ1 = 7.04µs and

τ2 =

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5.26µs have been obtained for both green emissions located at 523 nm (19120cm-1) and at 541

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nm (18484cm-1) assigned respectively to the 2H11/2 → 4I15/2 transition and to the 4S3/2 →4I15/2

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transition. The red emission centered on 652 nm (≈ 15337 cm-1) assigned to the 4F9/2 →4I15/2

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transition with τ3= 3.69µs; where: τ1, τ2 and τ3 are fluorescence lifetime components

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contributing to the average lifetime. It is worth pointing that all impurities introduced,

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structural defects, water molecule vibration modes (Jaba et al., 2010) [41] and OH groups [49]

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may be invoked for explaining the very short fluorescence decay time of the 2 H11/2, 4S3/2 and

220 221

4

F9/2.

4. Conclusions

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The structure of the NH4Er(PO3)4 polyphosphate has been determined by single crystal

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X-ray diffraction. In this structure, erbium atoms are coordinated by eight oxygen atoms

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forming ErO8 polyhedra isolated from each other. These polyhedra serve as links between

225

(PO3)n spiral chains of corner-sharing PO4 tetrahedra, that run along the [101] direction. The

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infrared and Raman spectroscopy results are in agreement with the structure. Absorption and

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PL measurements have been performed at RT. The decay curves for 2H11/2, 4S3/2 and 4F9/2

228

levels under UV-excitation wavelength are characterized by a short radiative lifetime. Under

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UV-excitation, a re-absorption phenomenon has been evoked as the main mechanism to

230

explain the appeared emission lines. NH4Er(PO3)4 showed an interesting emission at 1.53 µm

231

related to the 4I13/2→4I15/2 transition. The excitation spectrum shows that the position of the

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charge transfer band (CTB) is located between 230 nm and 300 nm, in agreement with most

233

phosphates. From these results, it appears that study is an interesting material for optical

234

applications.

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Acknowledgement

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This work is supported by the Ministry of Higher Education and Scientific Research in

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Tunisia.

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309

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310

Captions figures and tables

311

Fig. 1. Projection along the [100] direction of the NH4Er(PO3)4 structure.

312

Fig. 2. A partial view of the structure along [101] direction, showing the spirals chains.

313

Fig. 3. The association mode of the PO4 tetrahedra within the chains.

314

Fig. 4. The IR spectrum of NH4Er(PO3)4.

315

Fig. 5. The Raman scattering spectrum of NH4Er(PO3)4.

316

Fig. 6. The absorption spectrum of Er3+ in NH4Er(PO3)4 ( λex = 325 nm).

317

Fig. 7. A Plot of (αhν)2 versus photon energy (hν) of NH4Er(PO3)4 ; α: absorption coefficient.

318

Fig. 8. The emission photoluminescence spectrum of Er3+ in NH4Er(PO3)4 at room

319

temperature. (a) in the UV-Vis range, (b) in the IR range.

320

Fig. 9. UV-excitation spectrum of Er3+ in NH4Er(PO3)4 (λem = 657nm).

321

Fig. 10. Decay time profiles of both green ( 2H11/2→4I15/2, λem = 523 nm and 4S3/2→4I15/2, λem

322

= 541 nm) and red (4F9/2→4I15/2, λem = 652 nm) emissions of NH4Er(PO3)4 crystal under

323

excitation wavelength λexc= 375 nm.

324

Table 1 Crystal data, recording conditions and refinement results for NH4Er(PO3)4.

325

Table 2 Atomic coordinates and equivalent isotropic displacement parameters for

326

NH4Er(PO3)4.

327

Table 3 Selected bond distances (Å) and angles (°) in NH4Er(PO3)4.

328

Table 4 Distortion indices (ID) in the PO4 tetrahedra.

329

Table 5 Bond valence sums (BVS) for NH4Er(PO3)4 ∑exp and ∑th are the experimental and the

330

theoretical band valence sums(BVS).

331

Table 6 Raman and Infrared frequencies (cm-1) and their assignments.

332

Table 7 Excitation lines attribution of Er3+ in NH4Er(PO3)4.

333

Table 1 Crystal Data Diffractometer Empirical formula Formula weight (g. mol-1) Crystal system Space group Unit cell dimensions (Å)

Z Volume (Å3) ρcal(gcm-1)

CAD4 (Enraf-Nonius) NH4Er(PO3)4 501.18 Monoclinic P 21/n (no. 14) a = 10.259(3) b = 8.884(3) c = 10. 910(3) and 4 954.5(5) 3.49

β = 106.27(1)°

Data collection Crystal dimensions (mm3) Monochromator Scan type 2θmax (°) λ (Å) µ (mm-1) Limiting indices F (0 0 0) Number of measurement reflexions Number of unique reflexions; Rint Number of observed reflexions [I > 2σ (I)]

0.20 x 0.18 x 0.16 Graphite ω/2θ 33.06 0.71073 9.534 -15 ≤ h ≤ 15; 0 ≤ k ≤ 13; 940 3705 3550; Rint = 0.0126 3356

0 ≤ l ≤ 16

Structural refinement Absorption correction 2

Ψ scan

Goodness-of-fit on F 0.984 Theta range for data collection 3.01 – 33.06 Number of parameters 164 Extinction coefficient 0.0060 Weighting scheme w = 1/ (σ2 (I) + 0.1000 I2) Refinement method Full-matrix least-squares on F2 R [F2 > 2σ (F2)], wR (F2), S R1 = 0.0308, wR2 = 0.0923, S = 0.9840 -3 ∆ρmax, ∆ρmin (e .Å ) 2.282, -2.272 2 2 2 2 2 1/2 wR2 = (∑[W(F0 – Fc ) ] / [W(F0 ) ]) , R1 = ∑[|F0|-|Fc|] / ∑|F0| where W = 1 / [σ2(F20 ) + (0.0524P)2 + 21.5635P] and P = ( F20 + 2 Fc2 ) /3.

Table 2 Atoms Wyckoff

x

y

z

Ueq(Å2)

Er

4e

0.00149(3)

0.22447(2)

0.18677(6)

0.0069(9)

P1

4e

0.95991(10)

-0.17451(11)

0.14202(10)

0.0018(4)

P2

4e

0.17694(10)

0.39878(12)

0.48113(10)

0.0018(5)

P3

4e

0.75023(10)

0.97190(11)

0.22847(10)

0.0014(3)

P4

4e

0.95992(10)

0.82549(11)

0.14204(10)

0.0014(3)

O1

4e

0.0644(3)

0.2369(4)

0.9876(3)

0.0061(5)

O2

4e

0.2418(3)

0.1786(4)

0.2548(3)

0.0075(3)

O3

4e

0.1005(3)

0.4619(4)

0.1769(3)

0.0064(3)

O4

4e

0.0709(3)

0.2954(4)

0.4129(3)

0.0065(2)

O5

4e

0.8261(3)

0.4032(4)

0.1910(3)

0.0055(5)

O6

4e

0.8539(3)

0.0824(4)

0.2904(3)

0.0046(9)

O7

4e

0.8173(3)

0.1514(4)

0.0177(3)

0.0073(1)

O8

4e

0.0417(3)

0.9606(4)

0.1806(3)

0.0066(1)

O9

4e

0.1668(4)

0.5511(4)

0.4051(3)

0.0074(6

O10

4e

0.6442(3)

0.0407(4)

0.1066(3)

0.0040(8)

O11

4e

0.0198(3)

0.7011(4)

0.2461(3)

0.0059(1)

O12

4e

0.8171(3)

0.8434(3)

0.1665(3)

0.0041(7)

N

4e

0.3010(5)

0.4284(6)

0.0417(5)

0.0177(1)

H1

4e

1.3879(3)

0.4209(9)

0.1306(1)

0.0448(9)*

H2

4e

1.2544(9)

0.4803(4)

0.0050(9)

0.0400(1)*

H3

4e

1.2468(4)

0.3897(1)

0.0350(7)

0.0246(8)*

H4

4e

1.3429(8)

0.3978(1)

0.0077(8)

0.0159(4)*

Ueq is defined as one third of the trace of the orthogonalized Uij tensor; Ueq = 1/3∑i ∑j Uij ai* aj*aiaj *, isotropic displacement parameters

Table 3 ErO8 Er1 — O8 Er1 — O6 Er1 — O1 Er1 — O5 Er1 — O12 Er1 — O2 Er1 — O9 Er1 — O11

2.333(15) 2.357(4) 2.384(4) 2.402(8) 2.410(3) 2.437(7) 2.450(8) 2.475(8) 2.406(5)

O8 — Er1 — O6 O8 — Er1 — O1 O6 — Er1 — O1 O8 — Er1 — O5 O6 — Er1 — O5 O1 — Er1 — O5 O8 — Er1 — O12 O6 — Er1 — O12 O1 — Er1 — O12 O5 — Er1 — O12 O8 — Er1 — O2 O6 — Er1 — O2 O1 — Er1 — O2 O5 — Er1 — O2 O12 — Er1 — O2 O8 — Er1 — O9 O6 — Er1 — O9 O1 — Er1 — O9 O5 — Er1 — O9 O12 — Er1 — O9 O2 — Er1 — O9

118.47(12) 79.18(12) 142.98(12) 136.96(12) 75.39(11) 70.81(12) 75.81(11) 75.22(12) 141.66(12) 144.40(11) 70.44(11) 72.15(12) 85.88(11) 77.16(13) 111.90(12) 144.13(11) 78.98(11) 106.09(11) 75.46(12) 79.60(11) 144.23(11)

P(1)O4 P1 — O1 P1 — O2 P1 — O3 P1 — O4

1.457(4) 1.474(4) 1.569(4) 1.580(5) 1.520(1)

O1 — P1 — O2 O1 — P1 — O3 O2 — P1 — O3 O1 — P1 — O4 O2 — P1 — O4 O3 — P1 — O4

121.11(11) 110.60(9) 106.75(9) 107.06(14) 110.68(9) 98.27(9)

P(2)O4 P2 — O8 P2 — O9 P2 — O7 P2 — O10

1.452(5) 1.459(6) 1.575(4) 1.592(5) 1.520(1)

O8 — P2 — O9 O8 — P2 — O7 O9 — P2 — O7 O8 — P2 — O10 O9 — P2 — O10 O7 — P2 — O10

119.12(19) 108.79(20) 110.04(20) 107.46(19) 110.16(19) 99.44(18)

P(3)O4 P3 — O12 P3 — O11 P3 — O3 P3 — O10

1.464(6) 1.465(6) 1.578(5) 1.586(9) 1.524(2)

O12 — P3 — O11 O12 — P3 — O3 O11 — P3 — O3 O12 — P3 — O10 O11 — P3 — O10 O3 — P3 — O10

116.32(20) 108.99(18) 109.64(19) 107.89(18) 111.52(18) 101.42(18)

P(4)O4 P4 — O5 P4 — O6 P4 — O4 P4 — O7

1.448(4) 1.461(4) 1.566(4) 1.583(4) 1.515(2)

O5 — P4 — O6 O5 — P4 — O4 O6 — P4 — O4 O5 — P4 — O7 O6 — P4 — O7 O4 — P4 — O7

109.16(19) 109.94(12) 109.6(2) 109.39(22) 111.56(18) 97.38(19)

Table 4 Tetrahedron

P–Om

O–Om

O–P–Om

DI(P–O)

DI(O–O)

DI(O–P–O)

P1O4

1.520(1)

2.470

109.08

0.0358

0.0198

0.0463

P2O4

1.520(1)

2.472

109.23

0.0421

0.0112

0.0360

P3O4

1.524(2)

2.482

109.29

0.0385

0.0100

0.0306

P4O4

1.515(2)

2.463

107.84

0.0396

0.0185

0.0323

Table 5 exp

th

1.451

1.804

2

1.390

1.701

2

2.225

2

1.133

2.229

2

Atoms

Er

P1

O1

0.353

O2

0.311

O3

1.124

O4

1.096

P2

P3

P4

1.101

O5

0.338

1.485

1.823

2

O6

0.378

1.439

1.817

2

1.089

2.197

2

O7

1.108

O8

0.400

1.469

1.869

2

O9

0.301

1.446

1.747

2

1.082

2.149

2

O10

1.067

O11

0.283

1.426

1.709

2

O12

0.332

1.430

1.762

2

exp th

2.776 3

5.061 5

5.090 5

5.039 5

5.149 5

Table 6 IR frequencies (cm-1) 3273 3047

Intensity

1437 1412 1425

m vw vw

1297 1252

Raman frequencies (cm-1)

Intensity

Assignment

vs s δ (NH4+) 1313

s

1243

m

1229

vs

1180 1162 1143

vs vw m

s νas

-

νs

-

vs

1167 1148 1129 1117 1095 1084

sh m vw sh vw s

1064 1029 987 934 878

sh s m sh m

791 741 726 716

s vw m s

617 559 537 519 471

m vs s vw m

443 422 409

m sh m

1121 1104

sh vw

1063 1055 1036 971 864

m vw sh vw vw

736 725 716 713 703

vs s sh vw vw

556 520 483 467

w s m w w

418 404 389 340 313

m vw m m s

νas

νs

δ (PO)2

+ ν (M – O)

Table 7 Bands

Wavelength(nm)

Attribution

NH4Er(PO3)4 4

I15/2 → 2G9/2

a

367

b

394

4

I15/2 → 4F3/2

c

415

4

I15/2 → 4F5/2

d

444

4

I15/2 → 4F7/2

e

459

4

f

504

4

I15/2 → 4S3/2

g

533

4

I15/2 → 4F9/2

I15/2 → 2H11/2

Fig. 1

Fig. 2

Fig. 3

Fig. 4

Fig. 5

Fig. 6

Fig. 7

Fig. 8 (a)

(b)

Fig. 9

Fig. 10

388 389

390 391 392

Fig. 6

460 461

Highlights :

462

•

A structural study of NH4Er(PO3)4 is reported.

463

•

IR and Raman spectroscopy results are discussed.

464

•

A photoluminescence properties of NH4Er(PO3)4 are developed.

465

466 467

468 469 470 471 472

Figure 1: Projection along the [100] direction of the NH4Er(PO3)4 structure.