Sr₂Zn₃Te₂P₂O₁₄ as a Host for New Colored Compounds and Tunable White Light Emission

The compound, Sr₂Zn₃Te₂P₂O₁₄, was explored as a host to prepare new, brightly colored compounds and rare-earth ions based white light emission. All the compounds were synthesized at 750-880°C in air and characterized. The structure has Zn²⁺ ions in both tetrahedral as well as distorted square planar coordination. The substitution of transition elements such as Co²⁺, Ni²⁺, and Cu²⁺ ions in place of Zn²⁺ ions results in compounds exhibiting bright colors under daylight. The studies indicated that the Cu²⁺ ions prefer square-planar geometry, which was supported by UV-visible, EPR, and Raman spectroscopic studies. The substitution of P⁵⁺ ions by V⁵⁺ ions along with transition elements in place of Zn²⁺ ions results in compounds with different colors. The change in color is due to the metal-to-metal charge transfer (MMCT) transitions involving partially filled 3dⁿ electrons of the transition elements and empty 3d⁰ orbitals of V⁵⁺ ions. The near-IR reflectivity studies indicate that the white-colored compounds exhibit good near-IR reflectivity behavior, that are comparable to TiO₂. The substitution of rare-earth ions, namely, Eu³⁺, Tb³⁺, and Tm³⁺ ions in place of 8-coordinated Sr²⁺ ions results in characteristic emissions in the red, green, and blue regions, respectively. A careful manipulation of the concentration of these three ions (Eu³⁺, Tb³⁺, and Tm³⁺) resulted in white light emission for the composition Sr₂Zn₃Te₂P₂O₁₄: 1%Tm, 2% Tb, and 3% Eu. Based on the lifetime measurements, a possible schematic of the energy transfer pathway has also been proposed. The white-colored compounds exhibited reasonable dielectric constant values with low dielectric loss. Magnetic studies indicate anti-ferromagnetic interactions. The present study suggests that the telluro-phosphate compounds could be good candidates to explore many different physical and chemical properties.