Elusive Double Perovskite Iodides: Structural, Optical, and Magnetic Properties

Abstract

Halide double perovskites [A2MIMIIIX6] are an important class of materials that have garnered substantial interest as non‐toxic alternatives to conventional lead iodide perovskites for optoelectronic applications. While numerous studies have examined chloride and bromide double perovskites, reports of iodide double perovskites are rare, and their definitive structural characterization has not been reported. Predictive models have aided us here in the synthesis and characterization of five iodide double perovskites of general formula Cs2NaLnI6 (Ln=Ce, Nd, Gd, Tb, Dy). The complete crystal structures, structural phase transitions, optical, photoluminescent, and magnetic properties of these compounds are reported.

Hybrid Iodide Perovskites of Divalent Alkaline Earth and Lanthanide Elements

“…The Huang–Rhys factor and phonon frequency values for FAEuI 3 are S = 6 and ℏω = 151 cm –1 , respectively (Figure S10, eq S3). These values are consistent with values of S seen in other Eu­(II) systems , and the Raman vibrational frequencies seen in other lanthanide iodide systems. ,− In MAEuI 3 , the emission intensity decreases and the peak maxima red shifts from 441 nm (77 K) to 448 nm (300 K) with increasing temperature (Figure S8). The apparent transition between the Pnma and I 4/ mcm phases is also accompanied by a 4 nm red shift in luminescence maxima, between 200 and 225 K. This transition slightly affects the full width at half-maximum (fwhm) values at the transition; however, fitting the fwhm values to eq S3 through the transition gives values of S = 3 and ℏω = 146 cm –1 for MAEuI 3 (Figure S10).…”

“… The Goldschmidt Tolerance Factor has been widely used to predict whether a perovskite composition can form (0.8 < TF < 1.0) and if it will likely form an ideal cubic structure (0.9 < TF < 1.0). − The radius ratio has been used to determine if the M-site metal can support an octahedron of X – anions (X – = F – , Cl – , Br – , I – ). The combination of these two criteria has been used to predict large numbers of both hybrid and inorganic single and double perovskites. , For instance, we utilized both criteria to predict possible iodide double perovskites, which have since been realized by both ourselves and by Gamelin and co-workers . TF and radius ratio calculations suggest the possible existence of several new 3D-hybrid perovskite iodides by using divalent lanthanide and alkaline earth metal ions in the M II site (Figure , Table S1).…”

“…The combination of these two criteria has been used to predict large numbers of both hybrid and inorganic single and double perovskites. 19,21 For instance, we utilized both criteria to predict possible iodide double perovskites, 21 which have since been realized by both ourselves 22 and by Gamelin and coworkers. 23 TF and radius ratio calculations suggest the possible existence of several new 3D-hybrid perovskite iodides by using divalent lanthanide and alkaline earth metal ions in the M II site (Figure 1, Table S1).…”

Temperature and pressure induced structural transitions of lead iodide perovskites

“…Incorporation of other metal ions offers a new direction for chemical tunability in addition to structures. A very recent report on the iodide double perovskite Cs 2 NaLnI 6 (Ln = Ce, Nd, Gd, Tb, Dy) 142 family is one such example, presenting an opportunity to develop non-toxic (or less toxic) alternatives to lead iodide perovskites for magnetic and optoelectronic applications.…”

Synthesis of Metastable Silver-Lanthanide Double Perovskite Nanocrystals with White-Light Emission

“…19−23 These lanthanide perovskites display interesting properties, including the highest PLQY in the ultraviolet C (UV−C, 180−280 nm) range, 21 sharp near-infrared (NIR) photoluminescence at telecommunication wavelength (1260−1675 nm), 19 multimode and antithermal quenching luminescence, 22 and tunable bandgap and magnetic properties. 23 promising for optoelectronic applications. 24,25 It is worth noting that silver-lanthanide double perovskites have not been reported in any form, likely suggesting their metastability.…”