Enhanced Thermal Stability, Visible-Light Absorption, Band Gap Narrowing and Electrochemical Performance of Cr³⁺-doped Lithium Borate Glasses

Herein, we present the Cr ³⁺ -doped lithium borate glasses synthesised using the melt-quenching technique to examine the effects of Cr ³⁺ concentration (0 to 1 mol%) on their structural, microstructural, optical properties and electrochemical performance. The prepared glasses show a colour change from transparent to deep green with an increase in the concentration of Cr ³⁺ in the glasses, indicating successful doping and enhanced visible light absorption. The XRD analysis shows the amorphous nature, and the Raman analysis demonstrates the shifts in metal–oxygen vibrations from 324 to 372 cm ^− 1 , highlighting stronger Cr–O linkages and increased NBOs, leading to the increased thermal stability as shown by increased T _g values from 408°C to 428°C with Cr ³⁺ content. Optical absorption spectra showed a redshift and a broad Cr ³⁺ -related d–d transition near 600 nm. The indirect optical band gap decreased from 3.13 eV (base glass) to 2.11 eV (1 mol% Cr ³⁺ -doped glass), confirming band-gap narrowing due to Cr ³⁺ doping. Changes in structural disorder were suggested by a non-linear variation in Urbach energy. Electrochemical studies show the enhanced charge storage and redox reversibility, with 1 mol% Cr ³⁺ -doped glass (LBCr1.0) showing the low charge-transfer resistance (~ 6.8 Ω) and the maximum specific capacitance (57.2 Fg ^− 1 at 0.5 mA), indicating efficient ion transport and electrochemical stability, demonstrating their potential for photonic and energy storage applications.