Ratiometric and Colorimetric Optical Thermometers Using Emissive Dimeric and Trimeric {[Au(SCN)2 ]- }n Moieties Generated in d-f Heterometallic Assemblies

Nonlinear and Emissive {[MIII(CN)6]3-···Polyresorcinol} (M = Fe, Co, Cr) Cocrystals Exhibiting an Ultralow Frequency Raman Response

Optically active functional noncentrosymmetric architectures might be achieved through the combination of molecules with inscribed optical responses and species of dedicated tectonic character. Herein, we present the new series of noncentrosymmetric cocrystal salt solvates (PPh4)3[M(CN)6](L)n·msolv (M = Cr(III), Fe(III), Co(III); L = polyresorcinol coformers, multiple hydrogen bond donors: 3,3',5,5'-tetrahydroxy-1,19-biphenyl, DiR, n = 2, or 5'-(3,5-dihydroxyphenyl)-3,3″,5,5″-tetrahydroxy-1,19:3',1″-terphenyl, TriRB, n = 1) denoted as MDiR and MTriRB, respectively. The hydrogen-bonded subnetworks {[M(CN)6]3-;Ln}∞ of dmp, neb, or dia topology are formed through structural matching between building blocks within supramolecular cis-bis(chelate)-like {[M(CN)6]3-;(H2L)2(HL)2} or tris(chelate)-like {[M(CN)6]3-;(H2L)3} fragments. The quantum-chemical analysis demonstrates the mixed electrostatic and covalent character of these interactions, with their strength clearly enhanced due to the negative charge of the hydrogen bond acceptor metal complex. The corresponding interaction energy is also dependent on the geometry of the contact and size matching of its components, rotational degree of freedom and extent of the π-electron system of the coformer, and overall fit to the molecular surroundings. Symmetry of the crystal lattices is correlated with the local symmetry of coformers and {complex;(coformer)n} hydrogen-bonded motifs characterized by the absence of the inversion center and mirror plane. All compounds reveal second-harmonic generation activity and photoluminescence diversified by individual UV-vis spectral characteristics of the components, and interesting low-frequency Raman scattering spectra within the subterahertz spectroscopic domain. Vibrational (infrared/Raman), UV-vis electronic absorption (experimental and calculated), and 57Fe Mössbauer spectra together with electrospray ionization mass spectrometry (ESI-MS) data are provided for the complete description of our systems.

Luminescence and energy transfer performances of Tb3+/Mn4+ co-doped Sr2LuTaO6 double-perovskite phosphors for a highly sensitive optical thermometer

A series of Tb3+/Mn4+ co-doped double-perovskite oxides Sr2LuTaO6 (SLT) phosphors are synthesized by a solid-state method. The results of structural characterization prove that the Tb3+ and Mn4+ ions are successfully doped into the SLT host. The photoluminescence excitation (PLE) and photoluminescence (PL) spectra of Sr2LuTaO6:Tb3+, Sr2LuTaO6:Mn4+ and Sr2LuTaO6:Tb3+/Mn4+ are illustrated in detail. Under ultraviolet (UV) excitation, bright green and red lights are obtained from the Sr2LuTaO6:Tb3+/Mn4+ phosphor. In particular, the emission intensity of Tb3+ ions in Sr2LuTaO6:Tb3+/Mn4+ is enhanced by the energy transfer (ET) process from Mn4+ to Tb3+. The thermal enhancement of Tb3+ ion radiation in Sr2LuTaO6:Tb3+/Mn4+ also proves the ET process (Mn4+ → Tb3+). In addition, the thermal enhancement of Tb3+ ion radiation and the thermal quenching of Mn4+ ion radiation in the Sr2LuTaO6:Tb3+/Mn4+ system can be applied to develop optical thermometry based on luminescence intensity ratio (LIR) technology. Therefore, the LIRs of Mn4+ (2Eg → 4A2g) and Tb3+ (5D4 → 7F5,4) are investigated in the temperature range from 313 to 573 K. The absolute sensitivity (Sa) and relative sensitivity (Sr) of the Sr2LuTaO6:Tb3+/Mn4+ phosphor are calculated. The maximum values of Sa and Sr are obtained from the LIR of Tb3+: 5D4 → 7F4 (570-599 nm) and Mn4+: 2Eg → 4A2g (625-705 nm). The maximum Sa is 10.18% K-1 at 543 K, and the maximum value of Sr reaches 1.98% K-1 at 543 K. These results confirm that the ET process from Mn4+ to Tb3+ contributes to increasing the temperature measuring sensitivity of the Sr2LuTaO6:Tb3+/Mn4+ phosphor. Therefore, the Sr2LuTaO6:Mn4+/Tb3+ phosphor has prospective potential in optical thermometry and provides advantageous guidance for designing high-sensitivity optical thermometers.

Development of Nd (III)-Based Terahertz Absorbers Revealing Temperature Dependent Near-Infrared Luminescence

Molecular vibrations in the solid-state, detectable in the terahertz (THz) region, are the subject of research to further develop THz technologies. To observe such vibrations in terahertz time-domain spectroscopy (THz-TDS) and low-frequency (LF) Raman spectroscopy, two supramolecular assemblies with the formula [Nd^III (phen)₃ (NCX)₃] 0.3EtOH (X = S, 1-S; Se, 1-Se) were designed and prepared. Both compounds show several THz-TDS and LF-Raman peaks in the sub-THz range, with the lowest frequencies of 0.65 and 0.59 THz for 1-S and 1-Se, and 0.75 and 0.61 THz for 1-S and 1-Se, respectively. The peak redshift was observed due to the substitution of SCN⁻ by SeCN⁻. Additionally, temperature-dependent TDS-THz studies showed a thermal blueshift phenomenon, as the peak position shifted to 0.68 THz for 1-S and 0.62 THz for 1-Se at 10 K. Based on ab initio calculations, sub-THz vibrations were ascribed to the swaying of the three thiocyanate/selenocyanate. Moreover, both samples exhibited near-infrared (NIR) emission from Nd (III), and very good thermometric properties in the 300–150 K range, comparable to neodymium (III) oxide-based thermometers and higher than previously reported complexes. Moreover, the temperature dependence of fluorescence and THz spectroscopy analysis showed that the reduction in anharmonic thermal vibrations leads to a significant increase in the intensity and a reduction in the width of the emission and LF absorption peaks. These studies provide the basis for developing new routes to adjust the LF vibrational absorption.