Structural and Excitation-Dependent Photoluminescence Properties of Bi_0.95–xGd_xEu_0.05PO₄ (0 ≤ x ≤ 0.95) Solid Solutions and Their Anticounterfeiting Applications

Abstract

During the past few decades, lanthanide-doped luminescent nanomaterials have been widely applied in many fields, such as display devices, white light-emitting diodes (WLEDs), lasers, data storage, development of latent fingerprints, and anticounterfeiting. Herein, we report the synthesis of Bi0.95–x Gd x Eu0.05PO4 solid solutions through a co-precipitation method and their potential for anticounterfeit tags. The prepared samples show excellent photoluminescence properties and emit orange-red, yellowish-green, and fuchsia colors under 254, 365, and 394 nm UV illumination, respectively. Furthermore, the replacement of Bi3+ ions with Gd3+ in Bi0.95Eu0.05PO4 enhances the luminescent intensity due to energy transfer from Gd3+ to Eu3+ ions. Optimum luminescence properties are observed in the Bi0.50Gd0.45Eu0.05PO4 sample, and it is used for anticounterfeiting applications on various surfaces. The security patterns are printed on black paper and aluminum foil using luminescent ink containing Bi0.50Gd0.45Eu0.05PO4 nanomaterials. In addition, anticounterfeiting letters are directly written on different colored surfaces such as wood, black plastic, white plastic, and a colored plastic card. These security patterns/letters exhibit different colors under different UV irradiation wavelengths and are clearly visible with high contrast and sensitivity. These patterns are stable under various humidity and temperature conditions. The intensity of these patterns/letters remains unchanged under these conditions. From systematic investigations of the optical properties and stabilities, it has been proposed that the Bi0.50Gd0.45Eu0.05PO4 nanomaterials have the potential for unclonable anticounterfeiting tags to protect valuable documents/goods from counterfeiters.

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

“…Moreover, the radiative and nonradiative decay rates ( A rad , A nonrad ) were calculated to estimate the quantum efficiency ( η ) of the prepared nanophosphors. Here, the spontaneous emission cross section ( A 4− J ) of 5 D 4 → 7 F J ( J = 3, 4, 5, 6) transitions were estimated from the emission spectrum using the 4f – 4f intensity theory: 35 , where I 4− J and ν 4− J are the integral intensity and frequency corresponding to the 5 D 4 → 7 F J transition of Tb 3+ emission, respectively. The spontaneous emission cross section of the 4–6 transition ( A 4–6 ) is a constant with a value of 57.6 s −1 .…”

“…Moreover, the radiative and nonradiative decay rates (A rad , A nonrad ) were calculated to estimate the quantum efficiency (Z) of the prepared nanophosphors. Here, the spontaneous emission cross section (A 4ÀJ ) of 5 D 4 -7 F J ( J = 3, 4, 5, 6) transitions were estimated from the emission spectrum using the 4f-4f intensity theory: 35 total decay rate (A total = A rad + A nonrad ) is the reciprocal of the observed lifetime: A total = 1/t obs . Thus, A nonrad was calculated as: A nonrad = A total -A rad and the quantum efficiency of the prepared nanophosphors was determined using the expression: 36…”

Composition‐tunable SnSe(1−x)Sx (0 ≤ x ≤ 1) single crystals toward efficient bandgap engineering and optical/thermal properties

“…As the bandgap of semiconductor materials for optoelectronic and ther-moelectric applications is one of the most important characteristics, which indicates that obtaining SCs with tunable bandgaps is a crucial topic in this research area. Over the past decades, significant research efforts have been focused on adjusting the bandgap of the nanocrystals (NCs) through the introduction of cationic [17][18][19][20][21] or anionic [22][23][24][25] alloying of congeners. Nevertheless, there is a scarcity of systematic studies regarding similar alloying effects on larger sized SCs based on available knowledge.…”

Optimizing the luminescence efficiency of an europium (Eu3+) doped SrY2O4 phosphor for flexible display and lighting applications

“…With the excitation of 254 nm (UV region), europium ions are useful for light emitting phosphor and flexible display applications. 24–36 In this paper, we describe how to easily make new Eu 3+ doped SrY 2 O 4 phosphors, which may be utilized to improve the attractive performance of intelligent (smart) materials for flexible displaying applications. SYO:Eu phosphors emit red light when exposed to UV radiation.…”