Enhanced luminescence of Eu3+ in LaAl2B4O10 via energy transfer from Dy3+ doping

In this study, an investigation was conducted on the structural and photoluminescence (PL) characteristics of LaAl2B4O10 (LAB) phosphors initially incorporated with Dy3+ and Eu3+ ions. Subsequently, the impact of varying Eu3+ concentration while maintaining a constant Dy3+ concentration was examined. Structural characterization was performed using X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), and energy-dispersive X-ray spectroscopy (EDS). XRD analysis confirmed the effective embedding of both dopants into the hexagonal framework of the LAB. The PL emission spectra revealed characteristic emissions of Dy3+ (blue and yellow) and Eu3+ (red) ions. The optimized dopant concentrations of both Dy3+ and Eu3+ were observed to be 3 wt%. The dominant mechanism for concentration quenching in doped LAB phosphors was determined to be the electric dipole-dipole interaction. Co-doping with Eu3+ led to a substantial decrease in Dy3+ emission intensity (∼0.18-fold) while enhancing Eu3+ emission intensity (∼3.72-fold). The critical energy transfer distance (RC = 11.64 Å) and the analysis based on the Dexter theory confirmed that the energy transfer mechanism corresponds to dipole-dipole interaction. The color purities and correlated color temperatures (CCT) were estimated, suggesting the potential of these phosphors for warm white and red lighting applications, respectively. The observed energy transfer and luminescence properties, along with the structural and compositional characterization, highlight the promising potential of LAB:Dy3+/Eu3+ co-doped phosphors for advanced lighting and display technologies.

Tunable photoluminescence and energy transfer of Eu3+,Ho3+-doped Ca0.05Y1.93-xO2 nanophosphors for warm white LEDs applications

A series of Eu3+ ions doped Ca0.05Y1.93-xO3:0.02Ho3+ (CYO:Ho3+,xEu3+) nanophosphors having multicolour tuneability have been synthesised by following a simplistic solution combustion approach. The synthesised samples have been characterised by employing X-ray diffraction (XRD), Transmission electron microscope (TEM), and Fourier transforms infrared spectroscopy (FTIR). The optical properties have been engrossed by UV-visible and photoluminescent excitation and emission spectra, and decay lifetimes measurements. The characteristic emission, which occurs due to the f-f transition of Ho3+ and Eu3+ has been observed in emission spectra with excitation of 448 nm. By adjusting the doping ratio of Ho3+/Eu3+, the as-synthesized nanophosphor accomplishes multicolour tunability from green-yellow to red. Emission spectra and decay lifetime curve recommend dipole-dipole interaction causes energy transfer from Ho3+ → Eu3+. The energy transfer process from Ho3+ to Eu3+ has been confirmed through electric dipole-dipole interaction with critical distance 15.146 Å. Moreover, temperature dependent emission spectra show the high thermal stability with an activation energy ⁓ 0.21 eV, with the quantum efficiency of 83.6%. CIE coordinate illustrates that the singly doped Ho3+ and Eu3+ lie in the green and red region, respectively, while the as-synthesized CYO:Ho3+,xEu3+shows tunability from green to red with low CCT and high colour purity values. Hence, the CYO:Ho3+,xEu3+nanophosphor may be a near-UV excited multicolour colour-tunable pertinent candidate with potential prospects for multicolour- display and near-ultraviolet lighting applications.

Improvement of thermal stability and photoluminescence in Mg2Y2Al2Si2O12:Ce3+ by the cation substitution of Ca2+, Sr2+ and Ba2+ ions

The luminescence of Ce³⁺ in Mg₂Y₂Al₂Si₂O₁₂ (MgYAlSiO₆) can be controlled by substituting with Ca²⁺, Sr²⁺, and Ba²⁺ ions. The materials show blue shifts in their emission spectra that become highly evident with the increase in the ionic radius, and this phenomenon is the result of the combined action of the nephelauxetic effect and crystal field splitting. Due to the introduction of Ca²⁺, Sr²⁺, and Ba²⁺, the distortion of the crystal decreases and the structural rigidity and stability increase, improving the quantum efficiency and temperature stability of Mg₂Y_1.93Al₂Si₂O₁₂:0.07Ce³⁺. Mg₂Y_1.93Al₂Si₂O₁₂:0.07Ce³⁺,Ca²⁺ is more stable than Mg₂Y_1.93Al₂Si₂O₁₂:0.07Ce³⁺,Sr²⁺/Ba²⁺ because the radius of Sr²⁺/Ba²⁺ is larger than that of Mg²⁺. The Mg_1.9Y_1.93Al₂Si₂O₁₂:0.07Ce³⁺,0.1Ca²⁺ fluorescent powder and blue chip were packaged to obtain warm white light-emitting diodes (LEDs) with luminous efficiency of 60 lm W^-1. These results show that the Mg₂Y₂Al₂Si₂O₁₂:Ce³⁺ phosphor has potential application value in white LEDs.

Enhanced luminescence properties of Ca1+xSr2−xAl2O6:Eu3+ (0 ≤ x ≤ 1) red phosphors based on composition modulation

A series of Ca_1+xSr_2−xAl₂O₆:Eu³⁺ (0 ≤ x ≤ 1) red-emitting phosphors with adjustable optical properties and excellent quantum efficiency was developed for potential applications in warm WLEDs.

Recent progress of effect of crystal structure on luminescence properties of Ce3+–Eu2+ Co-doped phosphors

Currently, the mechanism of Ce³⁺–Eu²⁺ ET is frequently used to obtain color adjustable or white phosphors. Correspondingly, the ET efficiency from Ce³⁺ to Eu²⁺ becomes an important indication of the luminescent properties of phosphors. However, the ET efficiency calculated using the formula does not always match the emission spectra; the transmission efficiency of Ce³⁺ is high, but the emission efficiency of Eu²⁺ is low, depending on our investigation results. In addition to this problem, here we mainly review, on the basis of substantial examples, how to boost the actual ET efficiency of Ce³⁺-to-Eu²⁺ and thus to improve the luminescent properties of phosphors through the rational design of layered crystal structure and the way of selective occupation of activator ions. Moreover, the possible physical mechanisms are proposed.

Effect of crystal structure on luminescence properties of Ce³⁺–Eu²⁺ co-doped phosphors.