The absorption spectra of Sm²⁺ doped in MFX (M=Sr, Ba; X=Cl, Br) crystals were studied within the range of 20,000–35,000 cm^−1 as a function of temperature and host. The absorption bands observed were described with a simple model developed by Wood and Kaiser using group theory. The temperature and host dependence on the ⁷F₀→⁵D₃ Fano resonance lines were investigated. BaFCl:Sm²⁺ system showed a “normalâ€� ⁷F₀→⁵D₃ transition at 4 K in spite of similar crystal structure and absorption profile with other MFX hosts. New Fano resonances were observed in the absorption spectra at higher energies (23,000–25,000 cm^−1) for all MFX:Sm²⁺ systems at 4 K which persist up to room temperature. Preliminary energy level calculation showed that these resonance lines involve the interaction between higher excited ⁵L_J states of 4 f⁶configuration and 4 f⁵5d¹ configuration.

Europium doped crystalline Ba₇F₁₂Cl₂ phosphors have been prepared at temperatures between 650 and 900 °C using alkali chloride fluxes, yielding both disordered (with the incorporation of small amounts of Na) and ordered crystal modifications. The white emission spectrum excited in the near UV consists roughly of two broad emission bands at ca 450 and 590 nm, as well as weak sharp Eu²⁺ 4f-4f emission bands around 360 nm. The incorporation of Eu²⁺ is further studied using EPR spectroscopy on single crystals, and reveals a significant zero field splitting. The emission spectrum can be significantly tuned by varying the excitation wavelength between 300 and 390 nm. Fine tuning may also be achieved by chemical substitutions to form Ba_7-xM_yF₁₂Cl_2-zBr_z (M = Na, Ca,Eu). Quantitative measurements of the light produced using commercial near UV LEDs show that the color temperature ranges between 4000 and 9700 K with CIE chromaticity coordinates close to the ideal values of x=y=0.333. The best color rendering index (CRI) found was 0.83, and the highest light to light conversion yield was 171 lumen/W. These results show that the title compound is a very promising candidate for white light generation using near UV LED excitation.

Mixed matlokite hosts of composition BaFBr_xI_1−x(0≤x≤1) (pure and doped with Sm²⁺, Eu²⁺) were studied with x-ray crystallography, luminescence, Raman, and electron paramagnetic resonance (EPR) spectroscopy. Results are presented for BaFBr_0.5I_0.5 which demonstrate that a ferrielectric domain structure is formed due to the fact that the heavy halogen ions form separate sublattices with randomly distributed domain walls. The space group of a domain is P4  mm (No. 99). The EPR data from Eu²⁺ allowed to determine the volume fraction of domains.

Temperature-dependent emission spectra of Sm²⁺-doped SrMgF₄ have been obtained in the temperature range from 50 to 300 K. At 50 K, six bands are observed for the very strong ⁵D₀→⁷F₀ transition, in agreement with the reported sixfold crystal superstructure. The overall splitting of more than 70 cm^−1 highlights the important structural differences of the six Sr sites. Upon heating progressively to room temperature, the spectra change progressively with a more pronounced change between 270 and 300 K. These observations suggest the possibility of a complex structural behavior for SrMgF₄ which will require new experiments.

We recently discovered a new compound with composition Ba₇F₁₂Cl₂. It was possible to show that the variation of the synthesis conditions makes it possible to obtain a disordered and an ordered modification with different lattice parameters and space groups (P6₃/m [176] and P6  [174]). For Pb₇F₁₂Cl₂ an ordered modification is reported in the literature. In this paper we present the synthesis and structural characterization from X-ray diffraction data of the disordered modification of Pb₇F₁₂Cl₂. Single crystals were grown from a flux and the structure was refined in the hexagonal space group P6₃/m to R(R_w)=0.043(0.038) for 284 reflections and 26 parameters. Lattice parameters are a=b=1021.90(8) pm and c=361.93(6) pm with Z=1. Propeller-type arrangements with chlorine as axis and fluorines as blades are observed. The ordered modification of Pb₇F₁₂Cl₂ was prepared by a new hydrothermal synthesis. Differences between both modifications are found in the lattice constants and atomic occupation parameters for the atom type Pb2 and the connected fluorine ions.