Exploring the Impact of Structure-Sensitivity Factors on Thermographic Properties of Dy3+-Doped Oxide Crystals

Effect of A-Cation Radius on the Structure, Luminescence, and Temperature Sensing of Double Perovskites A2MgWO6 Doped with Dy3+ (A = Ca, Sr, Ba)

Herein, we report a case of A2MgWO6 (A = Ca, Sr, Ba) doped with 2%Dy3+, 2%Li+, in which the influences of the cation substitution are exhibited through the crystal structure, the charge transfer band (O2--W6+), the emission spectrum, the color of the luminescence, and the luminescent decay time. The substitution of Ca2+ and Sr2+ ions for larger ions (Ba2+) led to the crystal structure alteration from cubic to monoclinic and tetragonal, respectively. These structure changes also lowered the crystallography symmetry site of Dy3+, tuned the color of the emitted light from the whitish to yellowish region, and caused a blue shift of the CTB. Furthermore, a significant decline in the lifetime of the 4F9/2 → 6H13/2,15/2 transitions was noticed, from 748, 199, to 146 μs corresponding to Ba, Sr, Ca sample owing to the reduction in the local symmetry of Dy3+. Moreover, the thermal sensing properties of 2%Dy3+-doped samples were investigated based on the fluorescence intensity ratio technique in the range of 80-325 K. Under 266 nm excitation wavelength, the maximum relative sensitivity of the investigated samples was remarkably enhanced from 2.26%/K, 3.04%/K, to 4.38%/K corresponding to Ba, Ca, and Sr samples, respectively. In addition to providing a comprehensive understanding of the effects of compositional modifications on the optical properties, the results also present a viable pathway to manipulate the temperature sensing performance.

Luminescent Inorganic Mixed borate phosphors materials for lighting

The need of new materials with desirable optical properties has become important in recent year. In particular, a need has emerged for compounds having better luminescent properties in various practical applications. Introduction of rare earth ions as activators improves the luminescence properties of the compounds considerably. Boron is one of the most abundant elements in the nature. It readily combines with almost all other elements. In combination with oxygen; it forms borates comprising of various anions like BO₃ ^3- , B₂ O₅ ^4- , etc. Apart from these simple borates, several complex compositions exist involving mixed anions as well as double metal borates. Due to three-fold, or four-fold coordination of borate atoms Borates intrinsically possess characteristics that are advantageous for optical materials, which include wide transparency range, large electronic band gap, good thermal and chemical stability, low preparative temperature, optical stability with good nonlinear characteristics and exceptionally high optical damage threshold. The unique crystal structure of borates determines their enhanced UV transparency, good nonlinearity and relatively high resistance against laser induced damage. Some of these complex borates showing interesting luminescence properties are covered in this review. These include double borates containing rare earths RM₃ (BO₃ )₄ , Pentaborates LaMgB₅ O₁₀ , M₃ R₂ (BO₃ )₄ , where M is alkaline earth, mixed anion borates like aluminoborate SrAl₂ B₂ O₇ , Silicate-Borates like pekovite, SrB₂ Si₂ O₈ , Haloborates, M₂ B₅ O₉ X, where M is alkaline earth and X is halogen, phosphate borates, MBPO₅ , where M is alkaline earth. Phosphors base on these compositions find use in various applications like fluorescent lamps, colour TV, plasma display panels, high intensity discharge lamps based on Xenon, optically pumped solid state lasers, eye safe lasers, X-ray imaging.

Structure-Dependent Accessibility of Phonon-Coupled Radiative Relaxation Pathways Probed by X-ray-Excited Optical Luminescence

Rare-earth scheelites represent a diverse family of compounds with multiple degrees of freedom, which enables the incorporation of a wide range of lanthanide color centers. Precise positioning of quantum objects is attainable by the choice of alkali cations and lattice connectivity of polyanion units. Herein, we report the structure-dependent energy transfer and lattice coupling of optical transitions in La³⁺- and Dy³⁺-containing scheelite-type double and quadruple molybdates NaLa_1-xDy_x(MoO₄)₂ and Na₅La_1-xDy_x(MoO₄)₄. X-ray excitation of La³⁺ core states generates excited-state electron-hole pairs, which, upon thermalizing across interconnected REO₈ polyhedra in double molybdates, activate a phonon-coupled excited state of Dy³⁺. A pronounced luminescence band is observed corresponding to optical cooling of the lattice upon preferential radiative relaxation from a "hot" state. In contrast, combined X-ray absorption near-edge structure and X-ray-excited optical luminescence studies reveal that such a lattice coupling mechanism is inaccessible in quadruple molybdates with a greater separation of La³⁺-Dy³⁺ centers.