Ratiometric Thermometry Using Thermochromic Tb3+:Mn4+:Na4Mg(WO4)3 Phosphors

The utility of Tb³⁺:Mn⁴⁺:Na₄Mg(WO₄)₃ phosphors as ratiometric luminescent thermometers in the 200-450 K temperature range is demonstrated. Targeted substitution of Tb³⁺ for Na⁺ and Mn⁴⁺ for Mg²⁺ yields phosphors of formula Na_4-12xTb_4xMg_1-2yMn_y(WO₄)₃. UV excitation of the Na₄Mg(WO₄)₃ host results in green emission from terbium (544 nm) and red emission from manganese (682 nm). Differential thermal quenching of these emissions renders Na_3.976Tb_0.008Mg_0.990Mn_0.005(WO₄)₃ thermochromic between 78 and 450 K, with an orange-to-green color change that is particularly noticeable above 200 K. As a result, this phosphor serves as a ratiometric and colorimetric thermometer between 200 and 450 K. Quantitative assessment of its performance yields a maximum relative sensitivity of 2.5 × 10^-2 K^-1 at 375 K, along with a resolution of 0.5 K and a repeatability of 98%. These findings highlight the versatility of Na₄Mg(WO₄)₃ as a platform to realize luminescent thermometers via targeted aliovalent substitutions.

A powder method for the high-efficacy evaluation of electro-optic crystals

The electro-optic crystal holds great promise for extensive applications in optoelectronics and optical communication. However, the discovery of novel electro-optic crystals is sporadic due to the difficulties of large-sized crystal growth for electro-optic coefficient measurement. Herein, to address this issue, a high-efficacy evaluation method using accessible powder samples is proposed in which the second-harmonic-generation effect, infrared reflectance spectrum and Raman spectrum are introduced to predict the magnitude of the electro-optic coefficient. The calculated electro-optic coefficients of numerous reported electro-optic crystals through this approach give universal agreement to the experimental values, evidencing the validity of the strategy. Based on this method, CsLiMoO₄ is screened as a novel potential electro-optic crystal and a high-quality crystal is grown by the Czochralski technique for electro-optic coefficient measurement using the half-wave voltage method, the result of which is also comparable to the calculated value. Consequently, the evaluation strategy presented here will pave a new way to explore promising electro-optic crystals efficiently.

Three new phosphates, Cs8Pb4(P2O7)4, CsLi7(P2O7)2 and LiCa(PO3)3: structural comparison, characterization and theoretical calculation

Three new phosphates with a short cutoff edge were obtained, and the structural comparisons were discussed in detail.

Four alkali metal molybdates with two types of Mo–O chains, ABMo3O10 (A = Li, B = Rb; A = Li, Na, K, B = Cs): synthesis, structure comparison and optical properties

The effects of cation size on the framework structures of four stoichiometrically equivalent alkali metal molybdates were discussed in detail.

In-situ studies on the micro-structure evolution of A2W2O7 (A=Li, Na, K) during melting by high temperature Raman spectroscopy and density functional theory

In-situ high temperature Raman spectroscopic (HTRS) technique in combination with density functional theory (DFT) analysis has been adopted to investigate the micro-structure of solid and molten A₂W₂O₇ (A=Li, Na, K). The [WO₆] octahedra were found to be connected to each other by corner and edge sharing in the crystalline Li₂W₂O₇ and K₂W₂O₇ compounds. In the crystal lattice of Na₂W₂O₇, on the other hand, the [WO₄] tetrahedra and [WO₆] octahedra were found to coexist and paired by corner sharing. Although the structural diversity has clearly led to distinct Raman spectra of the crystalline A₂W₂O₇ compounds, the spectra of their melts tended to be analogous, showing the typical vibration modes of (W₂O₇)^2- dimer. A mechanism was then proposed to explain the structure evolution occurring during the melting process of A₂W₂O₇. The effect of A⁺ cation on the Raman bands of (W₂O₇)^2- dimer in molten A₂W₂O₇ has also been investigated. Both the wavenumber and full width at half-height (FWHH) of the characteristic band assigned to the symmetrical stretching vibration mode of WO_nb (non-bridging oxygen) in (W₂O₇)^2- were found to decrease in the sequence of Li⁺, Na⁺ and K⁺, indicating the cation effect on the mean bond length and its distribution range of WO_nb. In addition, the relative intensity of this band was also influenced by the cation and it was increased in the order of Li₂W₂O₇, Na₂W₂O₇ and K₂W₂O₇, which has been explained by the charge transfer process and confirmed by Mulliken overlap population analysis.

Three new phosphates with isolated P2O7units: noncentrosymmetric Cs2Ba3(P2O7)2and centrosymmetric Cs2BaP2O7and LiCsBaP2O7

Three new phosphates, a noncentrosymmetric (NCS) Cs₂Ba₃(P₂O₇)₂and centrosymmetric (CS) Cs₂BaP₂O₇and LiCsBaP₂O₇, have been synthesized from high-temperature solutions for the first time.

Na3Y3(BO3)4: a new noncentrosymmetric borate with an open-framework structure

A new noncentrosymmetric borate Na₃Y₃(BO₃)₄ was synthesized. It features a zeolite-type framework, which is extremely rare in borates.