K₂Sr₄(PO₃)₁₀: A Polyphosphate with Deep-UV Cutoff Edge and Enlarged Birefringence

Abstract

A new polyphosphate K 2 Sr 4 (PO 3 ) 10 is synthesized by a hightemperature solution method. This compound crystallizes in the triclinic space group of P1̅ , consisting of the 1D infinite [PO 3 ] ∞ chains and K and Sr ions between the chains. Compared with AM 2 (PO 3 ) 5 (A = K, Rb, Cs; M = Ba, Pb), K 2 Sr 4 (PO 3 ) 10 exhibits a more complex [PO 3 ] ∞ chain structure and more diverse metal cationic coordination environment. More importantly, K 2 Sr 4 (PO 3 ) 10 has both a deep-UV cutoff edge (<200 nm) and a significantly enlarged birefringence. First-principles calculations indicate that the birefringence of K 2 Sr 4 (PO 3 ) 10 is 0.017 at 1064 nm, about 2 times that of RbBa 2 (PO 3 ) 5 (0.008 at 1064 nm), which reaches a new height among the reported mixed alkali metal and alkaline earth metal phosphate. Theoretical calculations and structural analyses show that the enlarged birefringence of K 2 Sr 4 (PO 3 ) 10 mainly originates from the [PO 3 ] ∞ chains arranged in an inverted zigzag. This discovery introduces a new strategy for devising novel phosphate deep-UV optical crystals with a large birefringence.

Novel antimony phosphates with enlarged birefringence induced by lone pair cations

“…6, both compounds are biaxial crystals, and the obtained birefringence are Δ n = 0.034@1064 nm (CsSbPO) and Δ n = 0.045@1064 nm (NH 4 SbPOH), respectively. The first principles results show that these two compounds have relatively large birefringence compared with many other phosphates such as K 2 Sr 4 (PO 3 ) 10 (0.017@1064 nm), 4 RbBa 2 (PO 3 ) 5 (0.008@1064 nm), 1 β-CsBa 2 (PO 3 ) 5 (0.011@1064), 87 RbLiZnP 2 O 7 (0.01@1064) 88 and CsLiZnP 2 O 7 (0.014@1064). 88…”

“…Phosphates, an important branch of inorganic materials, have diverse structures and a wide range of applications as fluorescent substrate materials, battery materials, ion-exchange materials, linear and nonlinear opticacl materials, etc . 1–6 For phosphate-based optical materials with rigid [PO 4 ] tetrahedra as functional basic units (FBUs), they are resistant to absorption even in the deep UV region, usually have a wide transmission window, 7–9 and favor chemical and thermal stability. 10–12 In addition, [PO 4 ] tetrahedra can be further interconnected via sharing oxygen atoms to form different P–O polymers, such as P 2 O 7 , P 3 O 9 , (PO 3 ) ∞ , and so on.…”

Designing excellent UV birefringent materials through the synergistic interaction of two highly distorted functional groups

“…However, the introduction of SCALP often leads to a significant redshift in the cut off edge of compounds. In current research, to ensure the bandgap of compounds, two strategies are commonly employed: (1) Introducing alkali metals and alkaline earth metals without d–d and f–f transitions to prevent the redshift of the cut-off edges of the compounds, 30 such as K 2 Sr 4 (PO 3 ) 10 (6.20 eV), 31 Rb 3 MgB 5 O 10 (6.49 eV), 32 Cs 6 Mg 6 (PO 3 ) 18 (6.52 eV), 33 KBa 2( PO 3 ) 5 (7.43 eV); 34 (2) Introducing halogen ions with high electronegativity, which facilitates a blueshift in the cut-off edge of the compounds, 35 such as Rb 3 Pb 2 (CH 3 COO) 2 Br 5 (3.12 eV), 36 (NH 4 )SbCl 2 (SO 4 ) (4.54 eV), 37 CsBr·(H 2 SeO 3 ) 2 (5.19 eV), 38 KCl·(H 2 SeO 3 ) 2 (5.44 eV), 38 Na 2 B 6 O 9 F 2 (7.33 eV). 39…”