Traditional optical anti-counterfeiting materials suffer from the static and simplistic optical responses, rendering them vulnerable to replication and constraining practical utility. Addressing these challenges, the strategic design of multifunctional materials with tunable and dynamic optical properties offers a promising route to advanced, reliable, resilient anti-counterfeiting and rewritable information storage technologies. Herein, we report Bi 3+ and Er 3+ co-doped CaLuGaO 4 phosphor exhibiting multicolor luminescence, afterglow, and reversible photochromism. Emission color is tunable between blue and cyan by altering ultraviolet excitation wavelength or temperature, while up-conversion luminescence shifts from yellow-green to green with increased 980 nm excitation power or reduced irradiation distance. Additionally, Bi 3+ doping induces defect-associated blue afterglow and photochromic switching under 254 nm light, reversible by heat treatment or 395 nm light irradiation. These multifunctional features enable sophisticated anti-counterfeiting and encoded information storage, positioning CaLuGaO 4 :Bi 3+ ,Er 3+ as a next-generation smart optical material.
The pursuit of efficient red emitting Eu 2+ doped oxide is endless, aiming to replace the state-of-the-art CaAlSiN 3 :Eu 2+ nitride counterpart to achieve cheaper and more stable warm illumination. Herein, we identify a hitherto unreported CaLuGaO 4 olivine compound. The crystal structure of the compound is belong to orthorhombic Pnma . Phonon dispersion relations have no imaginary frequency, verifying thermodynamic stability of the crystal structure. It structurally contains an octahedral Ca 2+ site that definitely has strong crystal field splitting energy, which motivates us to incorporate it with Eu 2+ to realize red emission through 4 f 6 5 d 1 → 4 f 7 transition of the octhdedral Eu 2+ ion. This goal is achieved as found the divalent Eu 2+ is necessarily stabilized in this site under CO sintering atmosphere rather than H 2 /N 2 . The as-designed CaLuGaO 4 :Eu 2+ exhibits impressively appealing properties, i.e., intense red emission at 650 nm (λ ex = 450 nm), with high PLQY up to 86 % and good thermal stability in temperature range 10–500 K, marking it as a promising and formidable red phosphor in warm illumination. The excellent emission properties are theoretically revealed to associate with the closed-packed dimensional crystal structure with high Debye temperature equals 440 K, which reduces the non-radiative recombination loss. The investigations in electron-vibrational interaction in the Eu 2+ :5 d state disclosing the interaction is intermediate coupling regime with Huang-Rhys factor of 4.3. As a proof-of-concept experiment of the red phosphor for illumination, a prototype WLED possession of low CCT = 3917 K, high Ra = 92.2, and excellent luminous efficiency = 110 lm/W is constructed, and a portable rechargeable LED flashlight is assembled, by utilizing CaLuGaO 4 :Eu 2+ phosphor as a key red convector. Moreover, we have also demonstrated the phosphor synthesized under H 2 /N 2 can apply for latent fingerprint visualization.
A phosphor that emits both white light and broad near-infrared (NIR) light is of significant interest across various fields, as it enables both visual inspection and NIR spectroscopic detection. In this study, we designed Dy 3+ /Cr 4+ codoped CaLuGaO 4 phosphors that emit both white light and broad NIR light ranging from 1100 nm to 1700 nm when excited at 450 nm. The white light is produced by the 4 F 9/2 → 6 H 15/2 , 6 H 13/2 , 6 H 11/2 transitions of Dy 3+ . The broad NIR light arises from the 3 T 2 to 3 A 2 transition of Cr 4+ . Additionally, energy transfer from Dy 3+ to Cr 4+ occurs in the Dy 3+ /Cr 4+ codoped CaLuGaO 4 phosphors, allowing for tunable ratios of white light to NIR light by varying the concentrations of Dy 3+ and Cr 4+ . A phosphor-converted light-emitting-diode was constructed by encapsulating the synthesized phosphors around a commercial blue LED chip, demonstrating potential applications in lighting sources and non-destructive spectral analysis.
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