Synthesis,Structure And Properties Of UV/Deep-UV Aluminophosphate Optical Crystal Materials

The design and synthesis of ultraviolet?UV?and deep-ultraviolet?DUV?optical crystal materials are critical for the development of laser technology and photochemistry,especially for DUV nonlinear optical?NLO?crystal materials that can effectively extend the wavelength range of common laser sources.They play a vital role in military,aerospace,medical and scientific research and other major areas.In this dissertation,the high-temperature solid-state reaction was used to introduce the Al-O group with ample structure and alkali metal and alkaline earth metal cations without d-d and f-f transitions into the phosphate system.Four novel UV/DUV aluminophosphate optical crystal materials were designed and synthesized.Their structures and properties were further studied and we drew the following conclusions:?1?A novel UV aluminophosphate optical crystal,Li₆Na₃Sr₁₄Al₁₁P₂₂O₉₀,was designed and synthesized.The unit cell parameters are a=16.9643?3??,b=10.1943?1??,c=21.8245?4??,and?=?=90°,?=112.643?2?°,V=3483.39?11??³,Z=2.It crystallizes in the monoclinic C2/m space group.Its crystal structure consists of two different types of?3,6?-linked kgd topological layers[Al?PO₄?₂]^3-and[Al?Al₃O??PO₄?₇]^25-.The[Al?PO₄?₂]^3-2D layered structure is formed by the AlO₆ octahedra connected to the?₃-PO₄ by sharing the apex oxygen atom.However,the?3,6?-linked unique novel[Al?Al₃O??PO₄?₇]^25-2D layer contains oxygen-centered trinuclear Al clusters.What is more remarkable:the Al–O–Al bond formed by the high-temperature solid-state reaction is an anti-Lowenstein rule,which is rare in aluminophosphates.The performance characterization shows that the Li₆Na₃Sr₁₄Al₁₁P₂₂O₉₀with excellent thermal stability exhibits good UV transmission with the cut-off edge of230nm,which can be used as a potential UV optical crystal material.?2?Three kinds of new DUV aluminophosphate optical crystals NaBaAlP₂O₈,NaBa₂AlP₄O₁₄ and NaCa_8.5AlP₇O₂₈ were designed and synthesized.Their main structural features and properties are as follows:NaBaAlP₂O₈ crystallizes in monoclinic P2₁/c space group,the unit cell parameters are a=8.3625?2??,b=10.2117?3??,c=9.0357?2??,?=90°,?=91.094?2?°,?=90°,V=771.47?3??³,Z=4.This compound exhibits an[AlP₂O₈]^3-two-dimensional anion layered structure formed by[AlPO₆]^4-one-dimensional chain and Al₂P₂O₁₂ four-membered ring formed by alternately connecting PO₄ and AlO₄ co-oxygen,and Ba²⁺and Na⁺are respectively filled in inside the interlayer and the anion skeleton and acts as a balance charge.NaBa₂AlP₄O₁₄ belongs to the triclinic system and crystallizes in the central symmetry space group P-1.The unit cell parameters are a=7.6816?4??,b=8.6941?5??,c=9.0790?4??,?=73.3905?4?°,?=82.567?4?°,?=82.628?4?°,V=573.47?5??³,Z=2.The compound is composed of an AlO₆ octahedron connected to two P₂O₇ dimers through oxygen atoms to form[AlO₂?P₂O₇?₂]^9-clusters.Then the four-membered ring consisted of two AlO₆ octahedra and two P₂O₇ dimers is further connected to form a one-dimensional chain structure,in which both Ba²⁺and Na⁺are filled in the gap of the one-dimensional chain and play a role in balancing charge.Solid diffuse reflectance spectroscopy indicated that the UV cutoffs of NaBaAlP₂O₈ and NaBa₂AlP₄O₁₄were all significantly lower than 190nm,and the electronic structure and optical properties of the two compounds were further explained by density functional theory calculations,indicating that they can be used as potential DUV-NLO crystal materials..NaCa_8.5AlP₇O₂₈ crystallizes in the trigonal system polar R3c space group,with unit cell parameters a=10.3071?3??,b=10.3071?3??,c=37.199?2??,?=90°,?=90°,?=120°,V=3422.5?3??³,Z=6.The compound exhibits a zero-dimensional anion skeleton formed by isolated PO₄ tetrahedrons and isolated[Al?PO₄?₆]^15-clusters.Na⁺and Ca²⁺distributes around the zero-dimensional structure to balance the charge.Powder frequency-doubled signal measurements show that the compound has a weak second-harmonic generation?SHG?in the visible light region?approximately 0.2 times KDP?.In the ultraviolet region,the SHG is about0.5 times that of BBO,and in the ultraviolet region it is I phase-matchable.The calculation of dipole moments shows that SHG mainly originates from the anomalous twisted CaO₈polyhedron rather than the common PO₄ and AlO₆ anionic groups.The calculation of the density of states based on the density functional also further validates the main contribution of the CaO₈ polyhedron.Solid diffuse reflectance spectroscopy shows the UV cut-off edge is less than 190nm.The thermal performance test shows it has extremely high thermal stability;the compound is potential as a deep ultraviolet non-linear optical crystal.