Tunable luminescence of Eu 3+ ‐activated CaWO 4 nanophosphors via Bi 3+ incorporation

Exploring Optically Stable Reddish-Orange Fluorescent Magnetic Pigment (0.90)Y2O3:(0.10-x)Eu3+:(x)Bi3+ for Anti-counterfeiting Applications

The (0.90)Y2O3:(0.10-x)Eu3+:(x)Bi3+ nanophosphors (0.00 ≤ x ≤ 0.06) are synthesised using chemical combustion citrate route and characterized via X-ray diffraction, Raman spectroscopy, Fourier transform infrared spectroscopy, UV- visible and photoluminescence spectroscopy. The scanning electron micrographs indicate that the grain size of the phosphors ranges between 40 to 50 nm. The photoluminescence (PL) spectra, acquired under the excitation wavelength of 365 nm of ultraviolet light, show emission peaks at wavelengths 580 nm, 586-598 nm, 610 nm, 629-661 nm and 686-695 nm corresponding to the 5D0 → 7FJ electronic transitions of the Eu3+ ion with J = 0, 1, 2, 3 and 4, respectively. The most intense PL spectra at 611 nm (5D0 → 7F2), showcasing reddish-orange emission, indicate a higher concentration of Eu3+ ions in asymmetric sites within the Y2O3 host matrix. The presence of the distinct electronic transitions of Eu3+ in PL spectra acclaims that Bi3+ ions transfer their energy efficiently to Eu3+ ions in the matrix. Physical and chemical tests are being conducted on nanophosphors with Bi3+ substitutional doping of x = 0.02 and x = 0.04, both demonstrating intense PL emission. Magnetisation measurements suggest the soft magnetic nature of the nanophosphors, attributing it to the presence of Eu3+ ions in the 7F2 state. The highest PL intensity is seen in the nanophosphor (x = 0.04) with substitutional doping of 6% of Eu3+ and 4% of Bi3+ in Y2O3. This nanophosphor also demonstrates excellent optical stability in the investigated conditions and exhibits soft magnetic behaviour, positioning it as a promising material for incorporation as a fluorescent magnetic pigment in security ink applications. These features serve to prevent counterfeiting of secured documents both optically and magnetically.

Structural, optical spectroscopy and energy transfer features of Tb3+-activated (Y, Gd)F3 nanophosphors for UV-based LEDs

A 15-fold intense green emission at 545 nm is observed in a Tb3+-activated (Y, Gd)F3 nanophosphor with high Tb3+ content and minimal Gd3+ concentration.

Calcium Tungstate Doped with Rare Earth Ions Synthesized at Low Temperatures for Photoactive Composite and Anti-Counterfeiting Applications

A precursor was prepared using a co-precipitation method to synthesize crystalline calcium tungstate. The prepared precursor was dried in an oven at 80 °C for 18 h. The dried powders, prepared without a heat treatment process, were observed in XRD analysis to be a crystalline CaWO4 phase, confirming that the synthesis of crystalline CaWO4 is possible even at low temperature. To use this crystalline CaWO4 as a light emitting material, rare earth ions were added when preparing the precursor. The CaWO4 powders doped with terbium (Tb3+) and europium (Eu3+) ions, respectively, were also observed to be crystalline in XRD analysis. The luminescence of the undoped CaWO4 sample exhibited a wide range of 300~600 nm and blue emission with a central peak of 420 nm. The Tb3+-doped sample showed green light emission at 488, 545, 585, and 620 nm, and the Eu3+-doped sample showed red light emission at 592, 614, 651, and 699 nm. Blue, green, and red CaWO4 powders with various luminescence properties were mixed with glass powder and heat-treated at 600 °C to fabricate a blue luminescent PiG disk. In addition, a flexible green and red light-emitting composite was prepared by mixing it with a silicone-based polymer. An anti-counterfeiting application was prepared by using the phosphor in an ink, which could not be identified with the naked eye but can be identified under UV light.

Synthesis and optimization of photoluminescence properties in potential reddish orange emitting niobate phosphor for photonic device applications

A series of samarium ions (Sm³⁺ ) activated barium sodium niobate (Ba₂ NaNb₅ O₁₅ ) samples have been successfully synthesized via employing a solid-state reaction technique. Single phase, crystalline tetragonal Ba₂ NaNb₅ O₁₅ were formed and the crystallite size of the prepared sample varied with doping of Sm³⁺ ions. The scanning electron microscopy (SEM) images of Ba₂ NaNb₅ O₁₅ :Sm³⁺ illustrate that the particles possess a non-uniform spherical structure with some agglomeration. The prepared Ba₂ NaNb₅ O₁₅ :Sm³⁺ phosphors were efficiently excited with near-ultraviolet (n-UV) (406 nm) and emit strong visible emission peaks in the range 550-725 nm. The phenomenon of concentration quenching was detected after x = 0.10 mol of Sm³⁺ ions concentration for Ba₂ NaNb₅ O₁₅ , which arises due to non-radiative energy transfer through dipole-dipole interaction among activator ions. Colour coordinates (0.586, 0.412) for the optimized phosphor lies in the visible reddish orange region. A bi-exponential decay behaviour was observed for the photoluminescence decay curve of the optimized phosphor sample with an average decay time in milliseconds. The temperature dependent emission intensity confirms that the Ba_2-x NaNb₅ O₁₅ :xSm³⁺ (x = 0.10 mol) phosphor exhibits adequate thermal stability having high value of activation energy (ΔE = 0.201 eV). The comprehensive study and analysis of the as-prepared samples suggest that the intense reddish orange emitting thermally stable Ba₂ NaNb₅ O₁₅ :Sm³⁺ phosphor can act as a potential luminescent material in phosphor coated lighting, solar cells and other photonic devices.