A new langbeinite-type phosphate K₂GdHf(PO₄)₃: synthesis, crystal structure, band structure and luminescence properties

Langbeinite-type com­pounds are a large family that include phosphates, sulfates and arsenates, and which are accom­panied by inter­esting physical properties. This work reports a new disordered langbeinite-type com­pound, K₂GdHf(PO₄)₃ [dipotassium gadolinium hafnium tris­(phosphate)], and its structure as determined by single-crystal X-ray diffraction. Theoretical studies reveal that K₂GdHf(PO₄)₃ is an insulator with a direct band gap of 4.600 eV and that the optical transition originates from the O-2p→Hf-5d transition. A Ce³⁺-doped phosphor, K₂Gd_0.99Ce_0.01Hf(PO₄)₃, was prepared and its luminescence properties studied. With 324 nm light excitation, a blue emission band was observed due to the 5d¹→4f¹ transition of Ce³⁺. The average luminescence lifetime was calculated to be 5.437 µs and the CIE chromaticity coordinates were (0.162, 0.035). One may expect that K₂Gd_0.99Ce_0.01Hf(PO₄)₃ can be used as a good blue phosphor for three-colour white-light-emitting diodes (WLEDs).

Computing details

Data collection: APEX2 (Bruker, 2018); cell refinement: SAINT (Bruker, 2018); data reduction: SAINT (Bruker, 2018); program(s) used to solve structure: SHELXS (Sheldrick, 2015a); program(s) used to refine structure: SHELXL2018 (Sheldrick, 2015b); molecular graphics: SHELXL2018 (Sheldrick, 2015b); software used to prepare material for publication: SHELXTL2018 (Sheldrick, 2015b) and PLATON (Spek, 2020).

Dipotassium gadolinium hafnium tris(phosphate)

Crystal data

K2GdHf(PO4)3	Mo Kα radiation, λ = 0.71073 Å
Mr = 698.85	Cell parameters from 1108 reflections
Cubic, P213	θ = 2.7–24.6°
a = 10.3179 (7) Å	µ = 16.69 mm^−1
V = 1098.4 (2) Å^3	T = 296 K
Z = 4	Prism, colourless
F(000) = 1260	0.20 × 0.04 × 0.04 mm
Dx = 4.226 Mg m^−3

Data collection

Bruker SMART APEXII CCD area detector diffractometer	927 independent reflections
Radiation source: fine-focus sealed tube	888 reflections with I > 2σ(I)
Detector resolution: 83.33 pixels mm^-1	Rint = 0.045
ω scans	θmax = 28.3°, θmin = 2.8°
Absorption correction: multi-scan (SADABS; Bruker, 2018)	h = −11→13
Tmin = 0.051, Tmax = 0.709	k = −13→11
7436 measured reflections	l = −10→13

Refinement

Refinement on F^2	w = 1/[σ^2(Fo^2) + (0.0054P)^2 + 0.3204P] where P = (Fo^2 + 2Fc^2)/3
Least-squares matrix: full	(Δ/σ)max = 0.001
R[F^2 > 2σ(F^2)] = 0.018	Δρmax = 0.53 e Å^−3
wR(F^2) = 0.031	Δρmin = −0.58 e Å^−3
S = 1.08	Extinction correction: SHELXL2018 (Sheldrick, 2015b), Fc^*=kFc[1+0.001xFc^2λ^3/sin(2θ)]^-1/4
927 reflections	Extinction coefficient: 0.00042 (12)
61 parameters	Absolute structure: Flack x determined using 363 quotients [(I+)-(I-)]/[(I+)+(I-)] (Parsons et al., 2013)
1 restraint	Absolute structure parameter: 0.019 (11)

Special details

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

Refinement. A single-crystal with dimensions of 0.20 × 0.04 × 0.04 mm was mounted on a glass fiber for the single-crystal X-ray diffraction experiments. A set of intensity data was collected using a Bruker Smart APEX II CCD equipped with a graphite-monochromated Mo—Ka radiation source (λ = 0.71073 Å) with a tube power of 50 kV and 20 mA. The frames were collected at ambient temperature with a scan width of 0.5° in ω and integrated with the Bruker SAINT software package (Bruker, 2018) using a narrow-frame integration algorithm. The unit cells were determined and refined by least squares upon the refinement of XYZ-centeroids of reflections above 10 σ(I). Then the data was scaled for absorption using the SADABS programme of APEXII package. Intensities of all measured reflections were corrected for Lp and crystal absorption effects. The crystal structure of title complex K₂GdHf(PO₄)₃ were solved using the SHELX2018 crystallographic computing system (Sheldrick, 2015) and standardized using PLATON (Spek, 2003).

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

	x	y	z	Uiso*/Ueq	Occ. (<1)
K1	0.56920 (17)	0.56920 (17)	0.56920 (17)	0.0320 (7)
K2	0.7035 (2)	0.2035 (2)	0.2965 (2)	0.0410 (9)
Hf1	0.91688 (3)	0.58312 (3)	0.41688 (3)	0.01225 (14)	0.404 (4)
Gd1	0.91688 (3)	0.58312 (3)	0.41688 (3)	0.01225 (14)	0.596 (4)
Hf2	0.35145 (3)	0.35145 (3)	0.35145 (3)	0.01377 (14)	0.596 (4)
Gd2	0.35145 (3)	0.35145 (3)	0.35145 (3)	0.01377 (14)	0.404 (4)
P1	0.62435 (17)	0.53517 (17)	0.23556 (17)	0.0151 (4)
O1	0.5204 (6)	0.4510 (6)	0.2971 (6)	0.0499 (17)
O2	0.7445 (7)	0.5203 (7)	0.3167 (7)	0.057 (2)
O3	0.6512 (6)	0.4885 (5)	0.1003 (6)	0.0437 (15)
O4	0.5801 (5)	0.6745 (5)	0.2338 (5)	0.0389 (15)

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
K1	0.0320 (7)	0.0320 (7)	0.0320 (7)	−0.0012 (8)	−0.0012 (8)	−0.0012 (8)
K2	0.0410 (9)	0.0410 (9)	0.0410 (9)	−0.0009 (9)	0.0009 (9)	0.0009 (9)
Hf1	0.01225 (14)	0.01225 (14)	0.01225 (14)	0.00100 (13)	−0.00100 (13)	0.00100 (13)
Gd1	0.01225 (14)	0.01225 (14)	0.01225 (14)	0.00100 (13)	−0.00100 (13)	0.00100 (13)
Hf2	0.01377 (14)	0.01377 (14)	0.01377 (14)	0.00087 (13)	0.00087 (13)	0.00087 (13)
Gd2	0.01377 (14)	0.01377 (14)	0.01377 (14)	0.00087 (13)	0.00087 (13)	0.00087 (13)
P1	0.0132 (10)	0.0158 (9)	0.0161 (9)	−0.0039 (7)	−0.0030 (7)	0.0009 (7)
O1	0.039 (4)	0.054 (4)	0.057 (5)	−0.032 (3)	0.013 (3)	−0.002 (3)
O2	0.043 (4)	0.060 (5)	0.067 (5)	−0.015 (3)	−0.034 (4)	0.020 (4)
O3	0.053 (4)	0.043 (4)	0.035 (3)	−0.003 (3)	0.018 (3)	−0.014 (3)
O4	0.039 (3)	0.024 (3)	0.054 (4)	0.010 (3)	0.012 (3)	−0.006 (3)

Geometric parameters (Å, º)

K1—O3^i	2.963 (6)	K2—O2^viii	3.303 (7)
K1—O3^ii	2.963 (6)	K2—P1^viii	3.574 (3)
K1—O3^iii	2.963 (6)	K2—P1^ix	3.574 (3)
K1—O1	3.102 (7)	K2—P1	3.574 (3)
K1—O1^iv	3.102 (7)	Hf1—O3^x	2.150 (6)
K1—O1^v	3.102 (7)	Hf1—O3^viii	2.150 (6)
K1—O2	3.212 (8)	Hf1—O3^i	2.150 (6)
K1—O2^v	3.212 (8)	Hf1—O2^iii	2.157 (6)
K1—O2^iv	3.212 (8)	Hf1—O2^xi	2.157 (6)
K1—O2^i	3.327 (9)	Hf1—O2	2.157 (6)
K1—O2^ii	3.327 (9)	Hf2—O1	2.099 (5)
K1—O2^iii	3.327 (9)	Hf2—O1^v	2.099 (5)
K2—O4^vi	2.958 (6)	Hf2—O1^iv	2.099 (5)
K2—O4^v	2.958 (6)	Hf2—O4^vi	2.146 (5)
K2—O4^vii	2.958 (6)	Hf2—O4^xii	2.146 (5)
K2—O1^viii	3.176 (8)	Hf2—O4^xiii	2.146 (5)
K2—O1^ix	3.176 (8)	P1—O3	1.502 (6)
K2—O1	3.176 (8)	P1—O2	1.504 (6)
K2—O2	3.303 (7)	P1—O4	1.509 (5)
K2—O2^ix	3.303 (7)	P1—O1	1.519 (6)
O3^i—K1—O3^ii	96.41 (17)	O3^x—Hf1—O3^viii	95.6 (2)
O3^i—K1—O3^iii	96.41 (17)	O3^x—Hf1—O3^i	95.6 (2)
O3^ii—K1—O3^iii	96.41 (17)	O3^viii—Hf1—O3^i	95.6 (2)
O3^i—K1—O1	100.21 (19)	O3^x—Hf1—O2^iii	92.8 (3)
O3^ii—K1—O1	153.02 (18)	O3^viii—Hf1—O2^iii	171.4 (2)
O3^iii—K1—O1	102.63 (16)	O3^i—Hf1—O2^iii	82.1 (2)
O3^i—K1—O1^iv	153.02 (17)	O3^x—Hf1—O2^xi	82.1 (2)
O3^ii—K1—O1^iv	102.63 (16)	O3^viii—Hf1—O2^xi	92.8 (3)
O3^iii—K1—O1^iv	100.21 (19)	O3^i—Hf1—O2^xi	171.4 (2)
O1—K1—O1^iv	55.49 (17)	O2^iii—Hf1—O2^xi	89.8 (2)
O3^i—K1—O1^v	102.63 (16)	O3^x—Hf1—O2	171.4 (2)
O3^ii—K1—O1^v	100.21 (19)	O3^viii—Hf1—O2	82.1 (2)
O3^iii—K1—O1^v	153.02 (18)	O3^i—Hf1—O2	92.8 (3)
O1—K1—O1^v	55.49 (17)	O2^iii—Hf1—O2	89.8 (2)
O1^iv—K1—O1^v	55.49 (17)	O2^xi—Hf1—O2	89.8 (2)
O3^i—K1—O2	60.53 (15)	O3^x—Hf1—K1	132.85 (16)
O3^ii—K1—O2	156.92 (17)	O3^viii—Hf1—K1	114.41 (16)
O3^iii—K1—O2	85.92 (15)	O3^i—Hf1—K1	48.33 (16)
O1—K1—O2	45.22 (15)	O2^iii—Hf1—K1	58.1 (2)
O1^iv—K1—O2	99.52 (17)	O2^xi—Hf1—K1	128.55 (18)
O1^v—K1—O2	87.01 (18)	O2—Hf1—K1	55.0 (2)
O3^i—K1—O2^v	85.92 (15)	O3^x—Hf1—K1^iii	48.33 (16)
O3^ii—K1—O2^v	60.53 (15)	O3^viii—Hf1—K1^iii	132.85 (16)
O3^iii—K1—O2^v	156.92 (17)	O3^i—Hf1—K1^iii	114.41 (16)
O1—K1—O2^v	99.52 (17)	O2^iii—Hf1—K1^iii	55.0 (2)
O1^iv—K1—O2^v	87.01 (19)	O2^xi—Hf1—K1^iii	58.1 (2)
O1^v—K1—O2^v	45.22 (15)	O2—Hf1—K1^iii	128.55 (18)
O2—K1—O2^v	114.71 (9)	K1—Hf1—K1^iii	112.700 (12)
O3^i—K1—O2^iv	156.92 (17)	O3^x—Hf1—K1^xi	114.41 (16)
O3^ii—K1—O2^iv	85.91 (15)	O3^viii—Hf1—K1^xi	48.33 (16)
O3^iii—K1—O2^iv	60.53 (15)	O3^i—Hf1—K1^xi	132.85 (16)
O1—K1—O2^iv	87.00 (19)	O2^iii—Hf1—K1^xi	128.54 (18)
O1^iv—K1—O2^iv	45.22 (15)	O2^xi—Hf1—K1^xi	55.0 (2)
O1^v—K1—O2^iv	99.52 (17)	O2—Hf1—K1^xi	58.1 (2)
O2—K1—O2^iv	114.71 (9)	K1—Hf1—K1^xi	112.700 (12)
O2^v—K1—O2^iv	114.71 (9)	K1^iii—Hf1—K1^xi	112.700 (12)
O3^i—K1—O2^i	45.45 (15)	O1—Hf2—O1^v	86.9 (3)
O3^ii—K1—O2^i	53.05 (15)	O1—Hf2—O1^iv	86.9 (3)
O3^iii—K1—O2^i	111.22 (19)	O1^v—Hf2—O1^iv	86.9 (3)
O1—K1—O2^i	132.78 (18)	O1—Hf2—O4^vi	91.9 (2)
O1^iv—K1—O2^i	141.22 (18)	O1^v—Hf2—O4^vi	87.2 (2)
O1^v—K1—O2^i	95.76 (15)	O1^iv—Hf2—O4^vi	174.1 (2)
O2—K1—O2^i	104.69 (3)	O1—Hf2—O4^xii	174.1 (2)
O2^v—K1—O2^i	55.5 (2)	O1^v—Hf2—O4^xii	91.9 (2)
O2^iv—K1—O2^i	138.21 (12)	O1^iv—Hf2—O4^xii	87.2 (2)
O3^i—K1—O2^ii	111.22 (19)	O4^vi—Hf2—O4^xii	93.8 (2)
O3^ii—K1—O2^ii	45.45 (15)	O1—Hf2—O4^xiii	87.2 (2)
O3^iii—K1—O2^ii	53.05 (15)	O1^v—Hf2—O4^xiii	174.1 (2)
O1—K1—O2^ii	141.22 (18)	O1^iv—Hf2—O4^xiii	91.9 (2)
O1^iv—K1—O2^ii	95.76 (15)	O4^vi—Hf2—O4^xiii	93.8 (2)
O1^v—K1—O2^ii	132.78 (18)	O4^xii—Hf2—O4^xiii	93.8 (2)
O2—K1—O2^ii	138.21 (12)	O1—Hf2—K1	52.59 (18)
O2^v—K1—O2^ii	104.69 (3)	O1^v—Hf2—K1	52.59 (18)
O2^iv—K1—O2^ii	55.5 (2)	O1^iv—Hf2—K1	52.59 (18)
O2^i—K1—O2^ii	86.00 (17)	O4^vi—Hf2—K1	122.52 (15)
O3^i—K1—O2^iii	53.05 (15)	O4^xii—Hf2—K1	122.52 (15)
O3^ii—K1—O2^iii	111.22 (19)	O4^xiii—Hf2—K1	122.52 (15)
O3^iii—K1—O2^iii	45.45 (15)	O1—Hf2—K2^v	129.18 (18)
O1—K1—O2^iii	95.76 (15)	O1^v—Hf2—K2^v	52.5 (2)
O1^iv—K1—O2^iii	132.78 (18)	O1^iv—Hf2—K2^v	64.5 (2)
O1^v—K1—O2^iii	141.22 (18)	O4^vi—Hf2—K2^v	112.26 (15)
O2—K1—O2^iii	55.5 (2)	O4^xii—Hf2—K2^v	46.77 (15)
O2^v—K1—O2^iii	138.21 (12)	O4^xiii—Hf2—K2^v	131.77 (16)
O2^iv—K1—O2^iii	104.69 (3)	K1—Hf2—K2^v	77.102 (15)
O2^i—K1—O2^iii	86.00 (17)	O1—Hf2—K2^iv	64.5 (2)
O2^ii—K1—O2^iii	86.00 (17)	O1^v—Hf2—K2^iv	129.18 (18)
O4^vi—K2—O4^v	90.85 (18)	O1^iv—Hf2—K2^iv	52.5 (2)
O4^vi—K2—O4^vii	90.85 (18)	O4^vi—Hf2—K2^iv	131.77 (16)
O4^v—K2—O4^vii	90.85 (18)	O4^xii—Hf2—K2^iv	112.26 (15)
O4^vi—K2—O1^viii	149.05 (18)	O4^xiii—Hf2—K2^iv	46.77 (15)
O4^v—K2—O1^viii	59.54 (14)	K1—Hf2—K2^iv	77.102 (15)
O4^vii—K2—O1^viii	81.55 (16)	K2^v—Hf2—K2^iv	115.167 (11)
O4^vi—K2—O1^ix	81.55 (16)	O1—Hf2—K2	52.5 (2)
O4^v—K2—O1^ix	149.05 (18)	O1^v—Hf2—K2	64.5 (2)
O4^vii—K2—O1^ix	59.54 (14)	O1^iv—Hf2—K2	129.18 (18)
O1^viii—K2—O1^ix	118.60 (5)	O4^vi—Hf2—K2	46.77 (15)
O4^vi—K2—O1	59.54 (14)	O4^xii—Hf2—K2	131.77 (16)
O4^v—K2—O1	81.55 (16)	O4^xiii—Hf2—K2	112.26 (15)
O4^vii—K2—O1	149.05 (18)	K1—Hf2—K2	77.102 (15)
O1^viii—K2—O1	118.60 (5)	K2^v—Hf2—K2	115.168 (11)
O1^ix—K2—O1	118.60 (5)	K2^iv—Hf2—K2	115.166 (11)
O4^vi—K2—O2	103.51 (17)	O3—P1—O2	109.4 (4)
O4^v—K2—O2	81.15 (17)	O3—P1—O4	110.5 (4)
O4^vii—K2—O2	163.59 (15)	O2—P1—O4	110.7 (4)
O1^viii—K2—O2	82.04 (16)	O3—P1—O1	109.6 (4)
O1^ix—K2—O2	129.78 (19)	O2—P1—O1	106.9 (4)
O1—K2—O2	43.99 (15)	O4—P1—O1	109.6 (4)
O4^vi—K2—O2^ix	81.15 (17)	O3—P1—K1	166.9 (2)
O4^v—K2—O2^ix	163.59 (15)	O2—P1—K1	66.3 (3)
O4^vii—K2—O2^ix	103.51 (17)	O4—P1—K1	82.4 (2)
O1^viii—K2—O2^ix	129.78 (19)	O1—P1—K1	62.1 (3)
O1^ix—K2—O2^ix	43.99 (15)	O3—P1—K2	79.3 (2)
O1—K2—O2^ix	82.04 (16)	O2—P1—K2	67.4 (3)
O2—K2—O2^ix	86.8 (2)	O4—P1—K2	169.7 (2)
O4^vi—K2—O2^viii	163.59 (15)	O1—P1—K2	62.6 (3)
O4^v—K2—O2^viii	103.51 (17)	K1—P1—K2	87.73 (6)
O4^vii—K2—O2^viii	81.15 (17)	O3—P1—K1^xi	47.8 (3)
O1^viii—K2—O2^viii	43.99 (15)	O2—P1—K1^xi	62.0 (3)
O1^ix—K2—O2^viii	82.04 (16)	O4—P1—K1^xi	121.5 (2)
O1—K2—O2^viii	129.78 (19)	O1—P1—K1^xi	128.4 (3)
O2—K2—O2^viii	86.8 (2)	K1—P1—K1^xi	127.88 (6)
O2^ix—K2—O2^viii	86.8 (2)	K2—P1—K1^xi	67.25 (7)
O4^vi—K2—P1^viii	171.54 (11)	O3—P1—K2^iv	103.3 (3)
O4^v—K2—P1^viii	81.50 (11)	O2—P1—K2^iv	145.6 (3)
O4^vii—K2—P1^viii	92.86 (11)	O4—P1—K2^iv	45.3 (2)
O1^viii—K2—P1^viii	25.14 (10)	O1—P1—K2^iv	70.8 (3)
O1^ix—K2—P1^viii	106.88 (13)	K1—P1—K2^iv	84.01 (5)
O1—K2—P1^viii	115.33 (12)	K2—P1—K2^iv	130.81 (7)
O2—K2—P1^viii	71.87 (13)	K1^xi—P1—K2^iv	146.83 (6)
O2^ix—K2—P1^viii	105.32 (17)	P1—O1—Hf2	167.8 (5)
O2^viii—K2—P1^viii	24.87 (11)	P1—O1—K1	92.2 (3)
O4^vi—K2—P1^ix	92.86 (11)	Hf2—O1—K1	94.9 (2)
O4^v—K2—P1^ix	171.54 (11)	P1—O1—K2	92.2 (3)
O4^vii—K2—P1^ix	81.50 (11)	Hf2—O1—K2	95.8 (2)
O1^viii—K2—P1^ix	115.33 (12)	K1—O1—K2	102.8 (2)
O1^ix—K2—P1^ix	25.14 (10)	P1—O2—Hf1	156.4 (4)
O1—K2—P1^ix	106.88 (13)	P1—O2—K1	88.3 (3)
O2—K2—P1^ix	105.32 (17)	Hf1—O2—K1	91.6 (2)
O2^ix—K2—P1^ix	24.87 (11)	P1—O2—K2	87.7 (3)
O2^viii—K2—P1^ix	71.87 (13)	Hf1—O2—K2	115.7 (2)
P1^viii—K2—P1^ix	95.21 (7)	K1—O2—K2	97.7 (2)
O4^vi—K2—P1	81.50 (11)	P1—O2—K1^xi	94.4 (3)
O4^v—K2—P1	92.86 (11)	Hf1—O2—K1^xi	88.6 (2)
O4^vii—K2—P1	171.54 (11)	K1—O2—K1^xi	172.6 (2)
O1^viii—K2—P1	106.88 (13)	K2—O2—K1^xi	75.56 (18)
O1^ix—K2—P1	115.33 (12)	P1—O3—Hf1^xiv	150.2 (4)
O1—K2—P1	25.14 (10)	P1—O3—K1^xi	110.2 (3)
O2—K2—P1	24.87 (11)	Hf1^xiv—O3—K1^xi	98.85 (19)
O2^ix—K2—P1	71.87 (13)	P1—O4—Hf2^xv	135.7 (3)
O2^viii—K2—P1	105.32 (17)	P1—O4—K2^iv	113.4 (3)
P1^viii—K2—P1	95.21 (7)	Hf2^xv—O4—K2^iv	101.33 (19)
P1^ix—K2—P1	95.21 (7)

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