Multifunctional Ho3+ doped Ba2La4Zn2O10 phosphors: Photoluminescence and electrochemical properties for LEDs and energy storage devices

This study explores the synthesis and characterization of 1–9 mol% Ho³⁺ activated green-emitting Ba₂La₄Zn₂O₁₀ (BLZO: Ho³⁺) phosphors, fabricated via a facile solution combustion method. Structural and morphological analyses are conducted using X-ray diffraction (XRD) and transmission electron microscopy (TEM), confirming the formation of a tetragonal phase with phase purity and irregularly shaped particles averaging 50 nm in size. Under 452 nm excitation (⁵I₈→⁵G₆ + ⁵F₁), the phosphors exhibit characteristic Ho³ ⁺ emissions, prominently at 551 nm, corresponding to the ⁵S₂ + ⁵F₄→⁵I₈ transition, producing strong green luminescence. The optimal doping concentration is determined to be 5 mol%, beyond which photoluminescence (PL) intensity declined due to dipole-dipole interactions leading to concentration quenching. The synthesized phosphors demonstrated robust thermal stability, with an activation energy of 0.30 eV. Remarkably, the phosphors achieved excellent color purity (98.8 %) and a correlated color temperature (CCT) of 6223 K. Internal quantum efficiency (I_QE) reached 60.24 % under 452 nm excitation. Thermal stability tests at 423 K revealed minimal degradation, with 91 % luminescence retention. Sensitivity measurements yielded a relative sensitivity (S_r) of 3.06 % K⁻¹ and absolute sensitivity (S_a) of 0.0035 K⁻¹, showing enhanced sensitivity at an optimal Ho³⁺ concentration of 5 mol%. Electrochemical studies further highlight the multifunctional nature of BLZO:Ho³ ⁺ nanophosphors. Cyclic voltammetry (CV) and galvanostatic charge-discharge (GCD) analyses confirm pseudocapacitive behavior, with the highest specific capacitance of 280.52 F/g recorded for BLZO:9Ho³⁺ at a scan rate of 5 mV/s. Remarkably, the GCD cycling stability of BLZO:9Ho³⁺ exhibits 90.80 % capacitance retention over 5000 cycles, surpassing that of undoped samples. The observed performance underscores the potential of Ho³⁺ activated BLZO phosphors in green-emitting LEDs, display devices, optoelectronic components, and energy storage applications.