Silicate Phosphors BaGa₂Si₂O₈:Ln³⁺ (Er³⁺, Ho³⁺, Yb³⁺) Equipped with Intrinsic Optical Bistability toward Photonic Barcodes

Abstract

Optical bistability phenomenon is of vital significance for technological applications such as optical telecommunications. Herein, novel upconversion (UC) luminescence phosphors, Ln 3+ (Er 3+ , Ho 3+ )/Yb 3+ co-doped BaGa 2 Si 2 O 8 , were developed. Irradiated by 980 nm laser, the system showed intrinsic optical bistability (IOB) and two different optical responses were observed under the same incident pump power, signifying that these phosphors can play a role in optical switching devices. This nonlinear phenomenon mainly originated from the appearance of large amounts of Yb 3+ −Yb 3+ dimers in the title materials where the Yb 3+ ions kept a higher density compared with the activators. In addition, the compounds displayed excellent temperature sensing performance and controllable spectrum modulation behavior, and photonic barcodes with reliable security and simple fabrication were designed for anti-counterfeiting based on the latter. This work not only offers useful enlightenment for the development and application of phosphors but also enables a deep understanding of IOB in lanthanide-doped materials.

Multiwavelength Responsive Luminescence for Temperature Sensing and Visualized Information Encoding/Decoding Based on Er3+/Tb3+-Doped Ba2Ga2GeO7 Phosphors

“…Obviously, the increase of incident pump power does not result in the presence of any new emission band but enhances the existing emissions. As a nonlinear behavior, the relationship between UC emission intensity and laser excitation power can be described using the following formula: − where I up signifies the integrated luminescence intensity, P refers to the incident pump power, and n is the number of incident photons involved in the transition process of lanthanide ions from the ground state to the emitting excited state. The values of n can be deduced via calculating the slope of the double logarithmic plot of luminescence intensity versus the incident pump power, as shown in Figure b and d. The n values can be determined to be ∼1.88, 1.94, 2.37, 2.06, and 1.63, so it is concluded that the two-photon process is largely responsible for all the UC emissions.…”

“…Furthermore, the spectral purity is evaluated through calculating the integrated intensities of green and red emission bands to check the quality of the luminescence color in the materials. The spectral purity can be estimated according to eq : where I g and I r are the integrated intensities of green emission and red emission bands, respectively. It is indisputable that the S gr value is limited in the interval from −1 and +1, and the former means a pure red emission, while the latter represents a pure green emission.…”

“…As such, the transitions exhibit different responses to the temperature variation, implying that these transitions may be useful in temperature sensing based on the FIR technique. The relative luminescence intensities of M 1 and M 2 follow the Boltzmann distribution, and the FIR value can be expressed by eq : − where I represents the integrated emission intensity, and the following tables represent the energy level of the above parameters. Δ E is the energy gap between above levels, k B is the Boltzmann constant, and T is the temperature.…”

Lanthanide ions (Eu3+, Er3+, Pr3+) as luminescence and charge carrier centers in Sr2TiO4

“…1 However, one of the most important applications of lanthanides in their ionized form is realized in modern lighting technologies as active dopants in inorganic and/or organic matrices. Regarding inorganic phosphors, optically active ions are usually incorporated into the crystal lattice of different compounds, such as aluminates, 2,3 borates, 4,5 silicates, 6–8 and phosphates. 9–11 Among them, titanates, particularly Ruddlesden–Popper (RP) compounds, described by the chemical formula A n +1 B n O 3 n +1 attract more attention due to their layered perovskite type of structure that allows their use in photocatalysis, solar cells, optoelectronics, and solid-state lighting.…”

Multimodal and Multicolor Anti-counterfeiting Realized in CaCd2Ga2Ge3O12 with a Single Activator of Mn2+

“…At present, counterfeiting and information leakage seriously threaten people’s interests to physical and mental health. − Consequently, there is an urgent demand for new anti-counterfeiting technologies for minimizing economic damage and protecting public safety. − Compared to the traditional technologies, such as QR codes, bar code, hologram, watermarking, engraving gravure printing technology, and digital security technology, the luminescence anti-counterfeiting technique has been widely adopted due to its facile design, excellent concealment, and high stability. − However, most of the traditional fluorescent materials used for anti-counterfeiting have shortcomings such as monochrome emission and fixed excitation, which reduce the anti-counterfeiting level and can be easily forged. Therefore, it cannot satisfy the actual needs of people. − Thus, there is an urgent need to develop innovative multiple anti-counterfeiting luminescent materials with intentionally designed color or well-defined tunable properties for information security. , …”