ABSTRACT
The pursuit of high-quality phosphors exhibiting swift response to near-ultraviolet (n-UV) excitation, elevated quantum efficiency (QE), superior thermal stability, and impeccable light quality has been a focal point of investigation. In this research, we synthesized a novel K2La2B2O7:Ce3+,Tb3+ (KLBO:Ce3+,Tb3+) color-tunable phosphor that meets these requirements. KLBO:Ce3+ can be stimulated efficiently by the n-UV light and shows an intense blue emission centered at 437 nm. Notably, KLBO:0.04Ce3+ exhibits exceptional internal QE (IQE = 94%) and outstanding thermal stability (I423 K/I303 K = 88%). Optimization of doping compositions enables efficient Ce3+ â Tb3+ energy transfer, resulting in substantial enhancements in QE and thermal stability. Specifically, KLBO:0.04Ce3+,0.28Tb3+ achieves an IQE of 98% and a thermal stability of 97%, higher than those of most phosphors of the same type. White light-emitting diodes fabricated using phosphor samples emit warm white light characterized by high Ra (Ra = 96.6 and 93.4) and low CCT (CCT = 4886 and 4400 K). This study underscores the feasibility of enhancing phosphor QE and thermal stability through energy transfer mechanisms.
ABSTRACT
In an increasing manner, near-infrared phosphor-converted light-emitting diodes (NIR pc-LEDs) are considered to be exemplary light sources owing to their notable attributes of elevated output power, economical nature, and exceptional portability. NIR phosphors are critical components of NIR pc-LEDs. Herein, we report a novel blue light excitable NIR phosphor CaLu2ZrScAl3O12:Cr3+ (CLZSA:Cr3+) as a crucial and efficient broadband NIR emitter. The CLZSA:Cr3+ phosphor displays an intense NIR broadband emission peaking at 776 nm and with a full width at half-maximum (fwhm) of 140 nm. The designed material also exhibits superior resistance to thermal quenching, as the intensity of emission at 423 K remains at 80% of that at room temperature. The constructed NIR pc-LED device based on CLZSA:Cr3+ demonstrates a high total output power of 68.4 mW at a drive current of 100 mA, along with a high photoelectric conversion efficiency of 23.0%. Impressively, the high-power NIR pc-LEDs are utilized as light sources for remote control and non-invasive detection, resulting in the excellent performance and remarkable achievement.
ABSTRACT
The cation-equivalent substitution strategy has the ability to manipulate the luminescence color of phosphors and enhance their overall luminescence performance. A series of novel yellow feldspar-type 3D layered phosphors (Ca1-ySry)4MgAl2Si3O14:xEu2+ were synthesized using a high-temperature solid-state reaction. The solid solution phosphors belong to a tetragonal crystal system with a space group of P4Ì 21m and cell parameters of a = b = 7.75407-7.91794 Å, c = 5.04299-5.22543 Å, and V = 303.166-327.602 Å3. Under near-ultraviolet (n-UV) excitation, the luminescence color of the phosphor undergoes modulation from yellow-green (530 nm) to blue (467 nm) as the Sr2+ ion substitution ratio increases. This modulation is attributed to the gradual decrease in crystal field splitting energy. Additionally, both the Stokes shift and the full width of the luminescence spectra decrease. Furthermore, there is an increase in the quantum yield (QY) from 45.50 to 60.73%. Finally, the fabricated white-light-emitting diode devices emitted warm white light and achieved high Ra (Ra = 94, 96.6, 92.7) and low correlated color temperature (CCT = 3486, 3430, 3788 K), indicating that the prepared solid solution phosphors can be used as candidate materials for WLED lighting.
ABSTRACT
In this work, a series of BaSrGd4O8:xBi3+ blue phosphors was synthesized employing the high-temperature solid-state method. Phase purity of the samples was verified by X-ray diffraction and Rietveld refinement. Time-resolved photoluminescence spectra revealed the existence of two distinct Bi sites. Subsequent optimization of dopant types and doping levels in the batch led to an almost twofold increase in quantum efficiency. The introduction of Eu3+ into the phosphors facilitated the construction of an energy transfer pathway. As the concentration of Eu3+ was increased, the emission color changed from blue to purple and finally to red. In addition, the thermal stability and potential applications of the phosphors were extensively investigated. Finally, two WLED devices were successfully fabricated with color rendering indices of 96.27 and 92.18, and correlated color temperatures of 5198 and 2475 K. This underscores the prospective application of these phosphors in the field of high-quality warm WLEDs.
ABSTRACT
Most commercial phosphor-converted white light-emitting diodes (pc-WLEDs) are manufactured with blue LED chips and yellow-emitting Y3Al5O12:Ce3+ (YAG:Ce3+) garnet phosphor, but the lack of blue-green light in the spectrum results in a low color rendering index (CRI). In this paper, we synthesized Y3ScAl4O12:Ce3+ (YSAG:Ce3+) by replacing Al3+ in YAG:Ce3+ with Sc3+. The introduction of Sc3+ with a larger ionic radius through a cation substitution strategy causes lattice expansion, elongation of the Y-O bond, and ultimately a decrease in Ce3+ 5d level crystal field splitting. As a consequence, the emission spectrum undergoes a blue-shift of 10 nm. Furthermore, the YSAG:Ce3+ phosphor exhibits good thermal stability, and its emission intensity at 423 K is about 58% of that at 303 K. Moreover, the analysis of Eu3+ emission spectra demonstrates that the introduction of Sc3+ resulted in a slight reduction of the dodecahedral lattice symmetry. YSAG:Ce3+ effectively compensates for the lack of the blue-green region, and WLEDs with high color rendering index (90.1), low color temperature (4566 K) and high luminous efficiency (133.59 lm W-1) were prepared using the combination of YSAG:0.08Ce3+, CaAlSiN3:Eu2+ and 450 nm blue chips. These findings indicate that YSAG:Ce3+ garnet phosphor has potential to be used in high quality WLEDs.
ABSTRACT
Series of Eu2+/Eu3+-coactivated Li2CaSiO4 phosphors were prepared by solid-state reaction technique. All the samples emitted the unique emissions of Eu2+ and Eu3+ ions when excited by 395 nm, while the strongest emission intensity was received when x = 0.03. On the basis of theoretical discussion, it is evident that crossover relaxation should be responsible for the thermal quenching mechanism which was further proved by the unchanged lifetime at elevated temperature. Besides, through analyzing the inconsistent responses of the emission intensities of the Eu2+ and Eu3+ ions to the temperature, the optical thermometric properties of the designed phosphors were studied. By selecting different emissions of Eu3+ ions and combining with that of the Eu2+ ions, adjustable sensitivities were realized in the resultant phosphors. Furthermore, the sensitivities of the studied compound were also found to be greatly affected by the doping concentration. The maximum absolute and relative sensitivities of the synthesized compounds were 0.0025 K-1 and 0.289% K-1, respectively. These achieved results implied that the Eu2+/Eu3+-coactivated Li2CaSiO4 phosphors were promising candidates for optical thermometry. Additionally, this work also provided promising methods to modulate the sensitivities of the luminescent compounds by adjusting spatial mode and doping concentration.
