Studies on the melilite compound, Bi2ZnB2O7, as a host for new colored compounds and as a phosphor for rare-earth luminescence

The compound, Bi₂ZnB₂O₇, stabilized in the melilite structure, has been prepared and characterized. The partial substitution of transition elements (Co²⁺, Ni²⁺ and Cu²⁺ ions) in place of tetrahedral Zn²⁺ ions gave rise to colored compounds. The origin of the color in the compounds was understood based on the allowed d-d transitions. The near-IR reflectivity studies indicate reasonable NIR reflectivity with values in the range of 50–65%. The tetrahedral B³⁺ ions were partially replaced by Al³⁺ ions, giving rise to a new melilite analogue, Bi₂Zn(B_1.5Al_0.5)O₇. The Bi³⁺ ions, substituted by rare-earth ions (Eu³⁺, Tb³⁺ and Tm³⁺), resulted in compounds exhibiting intense red, green and blue emissions. The life-time studies indicated an average life time in the milliseconds region for all three substituted compounds. The substitution of the same ions in place of Y³⁺ ions in (Bi_1.9Y_0.1)ZnB₂O₇ compounds also resulted in a similar behaviour. The compounds, Bi₂ZnB₂O₇, Bi₂Zn(B_1.5Al_0.5)O₇, (Bi_1.75Y_0.25)ZnB₂O₇ and (Bi_1.75La_0.25)ZnB₂O₇, were examined for their dielectric behaviour at room temperature, which gave reasonably good values with minimal dielectric loss. The present studies clearly indicates that the melilite structure could be adaptable, though in a limited way, resulting in new colored compounds and excellent luminescence behaviour.

Graphical abstract

The compound, Bi₂ZnB₂O₇, was explored towards new colored compounds by substituting divalent transition metal ions Co²⁺/Ni²⁺/Cu²⁺ in place of Zn²⁺ ion in the compound. Substitution of rare-earth ions at the bismuth site gives rise to intense characteristic emission.