Design and Synthesis of a Series of Rare-Earth Coordination Polymer-Based Phosphors: Exploration of the White Light Emission Property

Abstract

Three sister rare-earth (RE) coordination-based phosphors [RE(3,5-pydc)_1.5(CO₂)_0.5(H₂O)₄]·2H₂O·CH₃OH (RE = Y, Eu, and Tb and pydc = 3,5-pyridine dicarboxylate) (compounds 1, 2, and 3) have been prepared at room temperature using the slow diffusion method. Also, we have synthesized a series of tri-RE metal-based phosphor materials (compounds 4 to 14) by varying the relative concentrations of Y, Tb, and Eu metal salts. X-ray diffraction studies on single crystals of 1, 2, and 3 confirmed that these coordination polymers are isostructural with a one-dimensional skeleton. The RE metal ions adopted distorted tricapped trigonal prismatic geometries in this series of compounds. The presence of zwitterionic carbamates in one of the pyridine nitrogen sites was observed through the combination of atmospheric CO₂. All three compounds have been characterized by thermogravimetric analysis, and infrared spectra and phase purity of the compounds have been validated through PXRD studies. The trimetal-based material (compound 14) Y_0.5Eu_0.25Tb_0.25 was found to be appropriate for showing white light emission in the solid state at 325 nm excitation and through CIE coordinates (0.329, 0.333) and a low correlated color temperature of 5658 K. A multicolor emission mechanism at different excitation wavelengths has been discussed in detail. The key factor for the white light emission was found to be the presence of three color emission centers with an optimum intensity ratio at a particular excitation wavelength.