Optical Anisotropy and Phase Transitions in Lead Halide Perovskites

Abstract

Optical anisotropy originates from crystalline structures with low symmetry and governs the polarization-dependent light propagation. Optical anisotropy is particularly important to lead halide perovskites that have been under intense investigation for optoelectronic and photonic applications, as this group of materials possesses rich structural phases that deviate from the high-symmetry cubic phase. Here we apply 2D optical Kerr effect spectroscopy to quantify the optical anisotropy in single-crystal methylammonium lead bromide (MAPbBr3). We determine the strong photon energy dependence of optical anisotropy near the band gap and show the dramatic change in optical anisotropy across phase transitions. We correlate the optical anisotropy with the structural anisotropy and demonstrate the tuning of optical anisotropy by alloyed Cs x MA1–x PbBr3 perovskite crystals.

Hydroxyfluorooxoborate Na[B3O3F2(OH)2]⋅[B(OH)3]: Optimizing the Optical Anisotropy with Heteroanionic Units for Deep Ultraviolet Birefringent Crystals

“…Theu nbiased F o ÀF c difference electron density maps (model without hydrogen) calculated from single-crystal data of NBF are given in Figure 2b.T he positive difference peaks clearly indicate the possible positions of hydrogens around O (2,4,6,7,8) atoms with the observation of strong hydrogenbonding interactions,w hile no difference peaks were found near the Fatoms,which provides theoretical evidence for the BÀFand OÀHb onds in NBF crystal.…”

“…Optical anisotropy (or birefringence) is the most critical parameter for birefringent materials working in any spectral regions,w hich originates from the dependence of dipole oscillators and refractive index, and it can be regarded as the results of functional unitsa rrangement along different directions. [4] Thus,t he key for the achievement of large birefringence lies on (i)A-site metal cations;( ii)the type of functional anionic unit and its arrangement in the lattice.The metal cations like M = Sn, Bi, Hg, etc.,c an form [MO n ] polyhedra with large deformability and thereby enhance the optical anisotropy and birefringence, [5] but they are always excluded in the alternative elements since crystals with them cannot be transparent down to the deep-UV spectral region. Of course,for deep-UV transparent crystals,the contribution from A-site metal cations,except for rare earth elements,can be ignored since the optical anisotropy of A-centered polyhedra is very small.…”

“…Optical anisotropy (or birefringence) is the most critical parameter for birefringent materials working in any spectral regions, which originates from the dependence of dipole oscillators and refractive index, and it can be regarded as the results of functional unit's arrangement along different directions [4] . Thus, the key for the achievement of large birefringence lies on (i) A‐site metal cations; (ii) the type of functional anionic unit and its arrangement in the lattice.…”

Hydroxyfluorooxoborate Na[B3O3F2(OH)2]⋅[B(OH)3]: Optimizing the Optical Anisotropy with Heteroanionic Units for Deep Ultraviolet Birefringent Crystals

“…Optical anisotropy (or birefringence) is the most critical parameter for birefringent materials working in any spectral regions,w hich originates from the dependence of dipole oscillators and refractive index, and it can be regarded as the results of functional unitsa rrangement along different directions. [4] Thus,t he key for the achievement of large birefringence lies on (i)A-site metal cations;( ii)the type of functional anionic unit and its arrangement in the lattice.The metal cations like M = Sn, Bi, Hg, etc.,c an form [MO n ] polyhedra with large deformability and thereby enhance the optical anisotropy and birefringence, [5] but they are always excluded in the alternative elements since crystals with them cannot be transparent down to the deep-UV spectral region. Of course,for deep-UV transparent crystals,the contribution from A-site metal cations,except for rare earth elements,can be ignored since the optical anisotropy of A-centered polyhedra is very small.…”

CsB3O4(OH)2: a new deep-ultraviolet birefringent crystal with [B3O4(OH)2] anionic group

“…15 These two key features are closely related to the selection of functional FBBs and their arrangement in the lattice. 5,16,17 Due to the unique boronoxygen (B-O) bonding mode, borates exhibit rich crystal structure types and wide optical transparency windows, and are the most promising candidate system for exploring potential nonlinear optical and birefringent materials. 2,18,19 In borates, the π-conjugated units, i.e., [BO 3 ] and [B 3 O 6 ] are excellent FBBs for constructing birefringent materials.…”