Surface topography and emission properties of Cr3+ ions in zinc–bismuth–borate glass ceramics for solid state lighting applications

Melt quenching method followed by one step heat treatment was employed to prepare five glass ceramics of composition 70B₂O₃–29 Bi₂O₃–(1-x)Cr₂O₃: xZnO (where x = 0.00, 0.25, 0.5, 0.75, and 1.00) in mol %. The surface topography, Vicker’s hardness, and luminescence properties of the prepared glasses have been investigated as a function of concentration of ZnO in the composition. Crystal size (thru watershed and threshold models) and roughness parameters of the synthesized glass surfaces were calculated by using Gwyddion software application. Higher number of crystals and lower average crystal size were observed in watershed model and threshold model at x = 0.50 mol %. X-ray diffraction analysis confirms the formation of crystalline phases such as Bi₄B₂O₉, Bi₆B₁₀O₂₄, ZnB₂O₄, ZnB₄O₇, ZnBi₂O₄, spinel-type ZnCr₂O₄, etc. The emission spectra have exhibited two distinct emission bands centered at ≈ 550 nm and ≈ 650 nm attributed to electronic transitions of Cr³⁺ (3d³) ions. CIE color coordinates (x, y) place these glass ceramics in the green-yellow region of the visible spectrum. This chromatic positioning suggests that the glass ceramics have potential applications as active laser media or LED sources.