Synthesis and Properties of the Ba2PrWO6 Double Perovskite.

We report details on the synthesis and properties of barium praseodymium tungstate, Ba2PrWO6, a double perovskite that has not been synthesized before. Room-temperature (RT) powder X-ray diffraction identified the most probable space group (SG) as monoclinic I2/m, but it was only slightly distorted from the cubic structure. X-ray photoelectron spectroscopy confirmed that the initial (postsynthesis) material contained praseodymium in both 3+ and 4+ charge states. The former (Pr3+) disappeared after exposure to UV light at RT. Photoluminescence studies of Pr3+ revealed that Ba2PrWO6 is an insulator with a band gap exceeding 4.93 eV. Pressure-dependent Raman spectroscopy excluded the possibility of a phase transition up to 20 GPa; however, measurements between 8 and 873 K signified that there might be a change toward the lower symmetry SG below 200 K. Electron paramagnetic resonance spectra revealed the presence of interstitial oxygen which acts as a deep electron trap.

High-Pressure Near-Infrared Luminescence Studies of Fe3+-Activated LiGaO2.

A 0.25% iron (Fe3+)-doped LiGaO2 phosphor was synthesized by a high-temperature solid-state reaction method. The phosphor was characterized utilizing X-ray diffraction (XRD), scanning electron microscopy (SEM), high-pressure photoluminescence, and photoluminescence decay measurement techniques using diamond anvil cells (DACs). The powder X-ray analysis shows that the phosphor is a ß polymorph of LiGaO2 with an orthorhombic crystallographic structure at room temperature. The SEM result also confirms the presence of well-dispersed micro-rod-like structures throughout the sample. The photoluminescence studies in the near-infrared (NIR) range were performed at ambient, low-temperature, and high-pressure conditions. The synthesized phosphor exhibits a photoluminescence band around 746 nm related to the 4T1 → 6A1 transition with a 28% quantum efficiency at ambient conditions, which shifts toward longer wavelengths with the increase of pressure. The excitation spectra of Fe3+ are very well fitted with the Tanabe-Sugano crystal-field theory. The phosphor luminescence decays with a millisecond lifetime. The high-pressure application transforms the ß polymorph of LiGaO2 into a trigonal α structure at the pressure of about 3 GPa. Further increase of pressure quenches the Fe3+ luminescence due to the amorphization process of the material. The prepared phosphor exhibits also mechanoluminescence properties in the NIR spectral region.

Correction to "Synthesis Attempt and Structural Studies of Novel A2CeWO6 Double Perovskites (A2+ = Ba, Ca) in and outside of Ambient Conditions".

[This corrects the article DOI: 10.1021/acsomega.2c00669.].

Synthesis Attempt and Structural Studies of Novel A2CeWO6 Double Perovskites (A2+ = Ba, Ca) in and outside of Ambient Conditions.

This comprehensive work showcases two novel, rock-salt-type minerals in the form of amphoteric cerium-tungstate double perovskite and ilmenite powders created via a high-temperature solid-state reaction in inert gases. The presented studies have fundamental meaning and will mainly focus on a detailed synthesis description of undoped structures, researching their possible polymorphism in various conditions and hinting at some nontrivial physicochemical properties like charge transfer for upcoming optical studies after eventual doping with selectively chosen rare-earth ions. The formerly mentioned, targeted A2BB'X6 group of compounds contains mainly divalent alkali cations in the form of XIIA = Ba2+, Ca2+ sharing, here, oxygen-arranged clusters (IIX = O2-) with purposely selected central ions from f-block VIB = Ce4/3+ and d-block VIB' = W4/5/6+ since together they often possess some exotic properties that could be tuned and implemented into futuristic equipment like sensors or energy converters. Techniques like powder XRD, XPS, XAS, EPR, Raman, and FTIR spectroscopies alongside DSC and TG were involved with an intent to thoroughly describe any possible changes within these materials. Mainly, to have a full prospect of any desirable or undesirable phenomena before diving into more complicated subjects like: energy or charge transfer in low temperatures; to reveal whether or not the huge angular tilting generates large enough dislocations within the material's unit cell to change its initial properties; or if temperature and pressure stimuli are responsible for any phase transitions and eventual, irreversible decomposition.

Hole Trapping Process and Highly Sensitive Ratiometric Thermometry over a Wide Temperature Range in Pr3+-Doped Na2La2Ti3O10 Layered Perovskite Microcrystals.

We demonstrate a potential optical thermometric material, Pr3+-doped triple-layered perovskite Na2La2Ti3O10 microcrystals, which promises a remarkable performance in temperature sensing over a wide temperature range (125-533 K), with a maximum relative sensitivity of 2.43% K-1 at 423 K. Both temperature and high-pressure dependent photoluminescence measurements were performed for this compound. It turns out that the Pr3+-Ti4+ intervalence charge transfer state is the primary cause for the very efficient thermometric characteristics in the 296-533 K range. In the 125-300 K range, 3P1 and 3P0 levels of Pr3+ can be exploited as thermally coupled energy levels for temperature sensing with high sensitivity at and below room temperature. A significant enhancement of the Pr3+ ions' luminescence observed in the 4.5-300 K range is ascribed to an efficient, thermally activated energy transfer process from the host to Pr3+ ions. Carrier recombination on Pr3+ related hole traps was proposed in the studied system. The thermoluminescence properties are investigated, and possible mechanisms for the interpretation of the experimental results are discussed as well. This work may provide a perspective approach to design a high-performance, self-calibrated optical thermometer operating over a wide temperature range.