A new disordered langbeinite-type compound, K₂Tb_1.5Ta_0.5P₃O₁₂, and Eu³⁺-doped multicolour light-emitting properties

For the first time, a new langbeinite-type phosphate, namely potassium terbium tantalum tris­(phosphate), K₂Tb_1.5Ta_0.5(PO₄)₃, has been prepared successfully using a high-temperature flux method and has been structurally characterized by single-crystal X-ray diffraction. The results show that its structure can be described as a three-dimensional open framework of [Tb_1.5Ta_0.5(PO₄)₃]_∞ inter­connected by K⁺ ions. The Tb^III and Ta^V cations in the structure are disordered and occupy the same crystallographic sites. The IR spectrum, the UV–Vis spectrum, the morphology and the Eu³⁺-activated photoluminescence spectroscopic properties were studied. A series of Eu³⁺-doped phosphors, i.e. K₂Tb_1.5–xTa_0.5(PO₄)₃:xEu³⁺ (x = 0.01, 0.03, 0.05, 0.07, 0.10), were prepared via a solid-state reaction and the photoluminescence properties were studied. The results show that under near-UV excitation, the luminescence colour can be tuned from green through yellow to red by simply adjusting the Eu³⁺ concentration from 0 to 0.1, because of the efficient Tb³⁺→Eu³⁺ energy-transfer mechanism.

Computing details

Data collection: APEX2 (Bruker, 2016); cell refinement: SAINT (Bruker, 2016); data reduction: SAINT (Bruker, 2016); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL2014 (Sheldrick, 2015b); molecular graphics: SHELXL2014 (Sheldrick, 2015); software used to prepare material for publication: SHELXTL (Sheldrick, 2008).

Potassium terbium tantalum tris(phosphate)

Crystal data

K2Tb1.5Ta0.5(PO4)3	Mo Kα radiation, λ = 0.71073 Å
Mr = 691.96	Cell parameters from 905 reflections
Cubic, P213	θ = 2.8–24.5°
a = 10.3262 (6) Å	µ = 15.77 mm^−1
V = 1101.09 (19) Å^3	T = 296 K
Z = 4	Block, colourless
F(000) = 1252	0.18 × 0.17 × 0.15 mm
Dx = 4.174 Mg m^−3

Data collection

Bruker SMART APEXII CCD area detector diffractometer	927 independent reflections
Radiation source: fine-focus sealed tube	907 reflections with I > 2σ(I)
Detector resolution: 83.33 pixels mm^-1	Rint = 0.045
ω scans	θmax = 28.2°, θmin = 2.8°
Absorption correction: multi-scan (SADABS; Sheldrick, 1996; Bruker, 2016)	h = −9→13
Tmin = 0.108, Tmax = 0.453	k = −13→13
7448 measured reflections	l = −13→10

Refinement

Refinement on F^2	w = 1/[σ^2(Fo^2) + 4.889P] where P = (Fo^2 + 2Fc^2)/3
Least-squares matrix: full	(Δ/σ)max = 0.006
R[F^2 > 2σ(F^2)] = 0.023	Δρmax = 0.56 e Å^−3
wR(F^2) = 0.043	Δρmin = −0.77 e Å^−3
S = 1.13	Extinction correction: SHELXL2016 (Sheldrick, 2015), Fc^*=kFc[1+0.001xFc^2λ^3/sin(2θ)]^-1/4
927 reflections	Extinction coefficient: 0.0030 (2)
61 parameters	Absolute structure: Flack x determined using 368 quotients [(I+)-(I-)]/[(I+)+(I-)] (Parsons et al., 2013)
1 restraint	Absolute structure parameter: 0.027 (13)

Special details

Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s. planes.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Ų)

	x	y	z	Uiso*/Ueq	Occ. (<1)
K1	0.5701 (2)	0.5701 (2)	0.5701 (2)	0.0351 (8)
K2	0.2043 (3)	0.2957 (3)	0.7043 (3)	0.0427 (11)
Tb1	0.58140 (4)	0.41860 (4)	0.91860 (4)	0.01756 (19)	0.806 (4)
Ta1	0.58140 (4)	0.41860 (4)	0.91860 (4)	0.01756 (19)	0.194 (4)
Tb2	0.15006 (4)	0.65006 (4)	0.84994 (4)	0.0194 (2)	0.694 (4)
Ta2	0.15006 (4)	0.65006 (4)	0.84994 (4)	0.0194 (2)	0.306 (4)
P1	0.4653 (2)	0.7390 (2)	0.8772 (2)	0.0208 (5)
O1	0.3272 (9)	0.7348 (9)	0.9196 (9)	0.061 (3)
O2	0.5147 (9)	0.6081 (8)	0.8461 (9)	0.058 (3)
O3	0.5473 (13)	0.7969 (11)	0.9841 (11)	0.082 (4)
O4	0.4798 (11)	0.8269 (11)	0.7635 (10)	0.072 (3)

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
K1	0.0351 (8)	0.0351 (8)	0.0351 (8)	−0.0008 (10)	−0.0008 (10)	−0.0008 (10)
K2	0.0427 (11)	0.0427 (11)	0.0427 (11)	0.0013 (11)	−0.0013 (11)	0.0013 (11)
Tb1	0.01756 (19)	0.01756 (19)	0.01756 (19)	0.00050 (16)	0.00050 (16)	−0.00050 (16)
Ta1	0.01756 (19)	0.01756 (19)	0.01756 (19)	0.00050 (16)	0.00050 (16)	−0.00050 (16)
Tb2	0.0194 (2)	0.0194 (2)	0.0194 (2)	0.00122 (17)	−0.00122 (17)	−0.00122 (17)
Ta2	0.0194 (2)	0.0194 (2)	0.0194 (2)	0.00122 (17)	−0.00122 (17)	−0.00122 (17)
P1	0.0252 (12)	0.0189 (11)	0.0181 (11)	0.0005 (9)	−0.0080 (9)	0.0038 (9)
O1	0.049 (6)	0.079 (7)	0.057 (5)	0.013 (5)	0.025 (5)	−0.008 (5)
O2	0.074 (6)	0.043 (5)	0.056 (5)	0.026 (4)	−0.005 (5)	−0.016 (5)
O3	0.113 (10)	0.077 (8)	0.058 (6)	0.017 (7)	−0.051 (6)	−0.024 (6)
O4	0.092 (8)	0.065 (6)	0.060 (6)	−0.023 (6)	−0.024 (6)	0.048 (5)

Geometric parameters (Å, º)

K1—O2	2.933 (10)	K2—O4^ix	3.295 (12)
K1—O2^i	2.933 (10)	Tb1—O4^iii	2.198 (9)
K1—O2^ii	2.933 (10)	Tb1—O4^ii	2.198 (9)
K1—O4^iii	3.086 (13)	Tb1—O4^x	2.198 (9)
K1—O4^iv	3.086 (13)	Tb1—O2^xi	2.205 (8)
K1—O4^v	3.086 (13)	Tb1—O2^ix	2.205 (8)
K1—O3^iii	3.121 (12)	Tb1—O2	2.205 (8)
K1—O3^iv	3.121 (12)	Tb2—O3^vii	2.089 (9)
K1—O3^v	3.121 (12)	Tb2—O3^xii	2.089 (9)
K2—O1^vi	2.974 (10)	Tb2—O3^ix	2.089 (9)
K2—O1^iv	2.974 (10)	Tb2—O1^iv	2.152 (10)
K2—O1^vii	2.974 (10)	Tb2—O1^xiii	2.152 (10)
K2—O3^viii	3.219 (15)	Tb2—O1	2.152 (10)
K2—O3^ix	3.219 (15)	P1—O2	1.481 (8)
K2—O3^iii	3.219 (15)	P1—O4	1.491 (8)
K2—O4^iii	3.295 (12)	P1—O1	1.492 (9)
K2—O4^viii	3.295 (12)	P1—O3	1.514 (10)
O4^iii—Tb1—O4^ii	90.1 (4)	O3^vii—Tb2—O1^iv	86.6 (4)
O4^iii—Tb1—O4^x	90.1 (4)	O3^xii—Tb2—O1^iv	172.7 (4)
O4^ii—Tb1—O4^x	90.1 (4)	O3^ix—Tb2—O1^iv	92.9 (4)
O4^iii—Tb1—O2^xi	172.4 (4)	O3^vii—Tb2—O1^xiii	92.9 (4)
O4^ii—Tb1—O2^xi	90.1 (4)	O3^xii—Tb2—O1^xiii	86.6 (4)
O4^x—Tb1—O2^xi	82.3 (4)	O3^ix—Tb2—O1^xiii	172.7 (4)
O4^iii—Tb1—O2^ix	82.3 (4)	O1^iv—Tb2—O1^xiii	94.3 (3)
O4^ii—Tb1—O2^ix	172.4 (4)	O3^vii—Tb2—O1	172.7 (4)
O4^x—Tb1—O2^ix	90.1 (4)	O3^xii—Tb2—O1	92.9 (4)
O2^xi—Tb1—O2^ix	97.5 (3)	O3^ix—Tb2—O1	86.6 (4)
O4^iii—Tb1—O2	90.1 (4)	O1^iv—Tb2—O1	94.3 (3)
O4^ii—Tb1—O2	82.3 (4)	O1^xiii—Tb2—O1	94.3 (3)
O4^x—Tb1—O2	172.4 (4)	O2—P1—O4	110.5 (6)
O2^xi—Tb1—O2	97.5 (3)	O2—P1—O1	111.5 (6)
O2^ix—Tb1—O2	97.5 (3)	O4—P1—O1	110.2 (6)
O3^vii—Tb2—O3^xii	86.1 (5)	O2—P1—O3	109.0 (6)
O3^vii—Tb2—O3^ix	86.1 (5)	O4—P1—O3	106.1 (6)
O3^xii—Tb2—O3^ix	86.1 (5)	O1—P1—O3	109.4 (7)

Symmetry codes: (i) y, z, x; (ii) z, x, y; (iii) −x+1, y−1/2, −z+3/2; (iv) y−1/2, −z+3/2, −x+1; (v) −z+3/2, −x+1, y−1/2; (vi) −x+1/2, −y+1, z−1/2; (vii) z−1, x, y; (viii) −z+1, x−1/2, −y+3/2; (ix) −y+1, z−1/2, −x+3/2; (x) −y+3/2, −z+1, x+1/2; (xi) −z+3/2, −x+1, y+1/2; (xii) x−1/2, −y+3/2, −z+2; (xiii) −z+1, x+1/2, −y+3/2.