Broadband blue-emitting CaLaGaO4:Bi3+ phosphors with persistent afterglow for High-CRI w-LEDs and advanced anti-counterfeiting applications

A series of un-doped and (0–9 mol %) Bi³⁺ doped CaLaGaO₄ phosphors exhibiting afterglow luminescence were synthesized using the solution combustion technique. UV–Vis absorption spectra showed that the synthesized phosphors possess a direct bandgap, with values of the 5.168 eV for the undoped sample and 3.874 eV for the sample doped with 5 mol % Bi³⁺. Under excitation at 361 nm, a broad emission band centered at 448 nm was detected in the 370–600 nm range at room temperature, attributed to the ³P₁→¹S₀ electronic transition of Bi³⁺ ions. Incorporating 5 mol % Bi³⁺ ions into the CaLaGaO₄ matrix resulted in intense blue luminescence centered at 448 nm, with a full width at half maximum (FWHM) of 90 nm, high color purity of 87.6 %, excellent thermal stability of 86.0 % of the integrated emission at 420 K, and an activation energy (E_a) of 0.30 eV. The optimal afterglow intensity and decay lifetime were observed at the 5 mol % Bi³⁺ doping level. Furthermore, the CaLaGaO₄:5Bi³⁺ phosphor retained 93.10 % of its original luminescence after 15 days of immersion in water and 92.82 % after 15 days in 85 % relative humidity. A high-performance white light emitting diode (w-LED) device was successfully fabricated by employing this unique CaLaGaO₄:5Bi³⁺ phosphor, excited by a 365 nm chip. The resulting phosphor-converted w-LED demonstrated an impressive colour rendering index (R_a) of 94.0 and a pleasant correlated color temperature (CCT) of 5426 K, indicating strong promise for lighting applications. Additionally, its functionality as a security ink reveals its suitability for encryption and anti-counterfeiting (AC) technologies. The study underscores its potential in advanced optical tagging systems, time-gated display technologies, and optical data storage. The successful creation and decoding of a luminescent quick response (QR) code, along with its time-resolved decay behavior, reinforce the capability of CaLaGaO₄:5Bi³⁺ phosphors in AC and security applications. Overall, this work provides important insights for the development of next-generation broadband blue-emitting phosphors tailored for high-CRI w-LEDs and data security technologies.