Abstract

This study presents a comparative spectroscopic investigation of natural Cr³⁺-bearing ruby and multiphase Al₂O₃-based ceramics derived from industrial waste. The natural corundum shows characteristic Cr³⁺ crystal-field absorption bands at ~405 and ~550 nm and sharp R-line emission near 693 nm, confirming a structurally ordered α-Al₂O₃ lattice. In contrast, the waste-derived ceramics exhibit charge-transfer-dominated absorption associated mainly with V⁵⁺ and Fe³⁺ under oxidizing firing conditions. Strong UV absorption (220–300 nm) and the absence of vanadium crystal-field transitions indicate predominant V⁵⁺ stabilization, consistent with chemical and phase analysis. The ceramics display high lightness (L* ≈ 93) and a yellow hue (b* = 10–23) governed by ligand-to-metal charge-transfer processes. The results demonstrate the effectiveness of combined UV–Vis and Raman spectroscopy for distinguishing crystal-field and charge-transfer mechanisms and for resolving dopant-related colour formation in alumina systems.