In this work, we report on the promising photoluminescent behavior of the cubic double perovskite Cs 2 NaBiCl 6 doped with Mn 2+ ions. Localized excitations centered on Bi 3+ ions in the host lattice strongly absorb near-UV light. In the undoped host compound, only very weak photoluminescence is observed, but in manganese-doped samples, energy transfer from Bi 3+ to Mn 2+ leads to intense orange-red photoluminescence. A broad emission peak centered at 590 nm is assigned to the 4 T 1 → 6 A 1 transition of octahedrally coordinated Mn 2+ . The excitation spectrum contains peaks at 294 and 354 nm that arise from 6s 2 → 6s 1 6p 1 excitations of Bi 3+ ions. If the chloride ions are partially replaced by bromide ions, the strongest excitation peak red-shifts to 375 nm. The lack of expensive reagents and toxic elements and the ability to tune the excitation and emission spectra through chemical substitution make Cs 2 NaBiCl 6−x Br x :Mn 2+ a promising phosphor system.

The halide double perovskite Cs2NaInCl6 doped with Sb3+ is shown to be a promising blue phosphor.

The n-type Sn2TiO4 phase was synthesized using flux methods and found to have one of the smallest visible-light bandgap sizes known that also maintains suitable conduction and valence band energies for driving photocatalytic water-splitting reactions. The Sn2TiO4 phase was synthesized using either a SnCl2 flux or a SnCl2/SnF2 peritectic flux in a 2:1 flux-to-precursor ratio heated at 600 and 400 °C for 24 h, respectively. The two types of salt fluxes resulted in large rod-shaped particles at 600 °C and smaller tetragonal prism-shaped particles at 400 °C. Surface photovoltage spectroscopy measurements produced a negative photovoltage under illumination >1.50 eV, which confirmed electrons as the majority charge carriers and ∼1.50 eV as the effective band gap. Mott–Schottky measurements at pH 9.0 showed the conduction (−0.54 V vs NHE) and valence band (+1.01 V vs NHE) positions meet the critical thermodynamic requirements for total water splitting. The Sn2TiO4 particles were deposited and annealed as polycrystalline films on FTO slides, and exhibited photoanodic currents in aqueous solutions under visible-light irradiation. The Sn2TiO4 particles were also suspended in aqueous methanol solutions and irradiated with visible and ultraviolet light. The larger rod-shaped Sn2TiO4 particles had the higher rates of photocatalytic hydrogen production (∼11.6 μmol H2 h–1) in comparison to the smaller tetragonal prism-shaped Sn2TiO4 particles (∼3.4 μmol H2 h–1). Conversely, for photocatalytic oxygen production, the rates for the smaller tetragonal prism-shaped particles in aqueous AgNO3 solution were slightly higher (∼16.3 μmol O2 h–1) than for the larger rod-shaped particles (∼11.9 μmol O2 h–1). Apparent quantum yields of 0.995% and 0.0098% were measured for O2 and H2 production, respectively, under 435 nm light.

Here, we present the synthesis and crystal structure of Rb3InCl6 prepared from air stable reagents via a two-step process that proceeds through the intermediate Rb2InCl5·H2O. Rb3InCl6 crystallizes with the Rb3YCl6 structure type (C2/c), which can be derived from the double perovskite structure by noncooperative tilting of isolated [InCl6]3– octahedra. Despite this lowering of symmetry, the optical properties are similar to the cubic double perovskite Cs2NaInCl6. Partial substitution of In3+ with Sb3+ in Rb3InCl6 results in intense cyan-green photoluminescence originating from localized 5s2 to 5s15p1 electronic transitions of [SbCl6]3– polyatomic anions. In comparison with the cubic double perovskite phosphor Cs2NaInCl6:Sb3+, the octahedral tilting distortion increases the electronic isolation of the In/Sb-centered octahedra thus facilitating electron and hole localization on Sb3+ sites, leading to bright photoluminescence. The distorted crystal structure also leads to a larger Stokes shift (1.29 eV) and a corresponding red shift of the emission peak (λmax = 522 nm) compared to the more symmetric Cs2NaInCl6:Sb3+ (Stokes shift ≈ 0.94 eV, λmax = 445 nm).