Near-ultraviolet Light-emitting Diode Chips Research Articles

Insight into the crystal structure and photoluminescence properties of an extremely broadband yellow-emitting phosphor Sr8MgCe(PO4)7:Eu2.

The combination of binary complementary color phosphors with near-ultraviolet (NUV) light-emitting diode (LED) chips was put forward to lower the energy loss caused by the reabsorption of the combination of tricolor phosphors with NUV LED chips. Thus investigating broadband yellow-emitting phosphors with enriched red components in the spectral range has gained much attention. Here, an extremely broadband yellow-emitting phosphor Sr8MgCe(PO4)7:Eu2+ with sufficient red component in the spectral region was synthesized. Due to the introduction of Ce into the host, Sr8MgCe(PO4)7 shows an emission band with a peak at 375 nm when excited at 310 nm. Meanwhile, Eu2+ doped Sr8MgCe(PO4)7 exhibits an extremely broad yellow emission band with a full width at half-maximum of 175 nm and a peak located at about 598 nm, due to the 5d-4f transitions of Eu2+ ions substituting five Sr2+ sites. The excitation peak of the host at 310 nm was detected in the excitation spectrum of Sr8MgCe(PO4)7:Eu2+ monitored at 598 nm, indicating the energy transfer from the host to Eu2+, which was also proved by the decay curves. On the other hand, the excitation band at about 400 nm due to the 4f-5d transitions of Eu2+ was also detected in the excitation spectrum of Sr8MgCe(PO4)7:Eu2+, and this matches well with the NUV LED chips. Moreover, the energy transfer between Eu2+ ions at different crystallographic sites was demonstrated by time-resolved photoluminescence (TRPL) spectra. A white LED with a CRI (Ra) of 82.88 and a CCT of 4238 K was prepared through a 400 nm NUV LED chip, Sr8MgCe(PO4)7:Eu2+ and BaMgAl10O17:Eu2+ (BAM:Eu2+). These results pave the way for designing better Eu2+-doped phosphors for NUV WLEDs with binary complementary color phosphors.

Eu3+-activated La2MoO6-La2WO6 red-emitting phosphors with ultrabroad excitation band for white light-emitting diodes

A series of novel Eu3+-activated La2MoO6-La2WO6 red-emitting phosphors have been successfully prepared by a citrate-assisted sol-gel process. Both photoluminescence excitation and emission spectra suggest that the resultant products have the strong ultrabroad absorption band ranging from 220 to 450 nm. Under the excitation of 379 nm, the characteristic emissions of Eu3+ ions corresponding to the 5D0 → 7FJ transitions are observed in the doped samples. The optimal doping concentration for Eu3+ ions is found to be 12 mol% and the quenching mechanism is attributed to the dipole-dipole interaction. A theoretical calculation based on the Judd-Ofelt theory is carried out to explore the local structure environment around the Eu3+ ions. The studied samples exhibit a typical thermal quenching effect with a T0.5 value of 338 K and the activation energy is determined to be 0.427 eV. A near-ultraviolet (NUV)-based white light-emitting diode (LED) is packaged by integrating a mixture of resultant phosphors, commercial blue-emitting and green-emitting phosphors into an NUV LED chip. The fabricated LED device emits glaring white light with high color rendering index (84.6) and proper correlated color temperature (6492 K). These results demonstrate that the Eu3+-activated La2MoO6-La2WO6 compounds are a promising candidate for indoor lighting as red-emitting phosphors.

Efficient red-emitting phosphor ScVO4 doped with Bi3+ and Eu3+ for near-ultraviolet-activated solid-state lighting

In this paper, Bi3+- and Eu3+-co-doped ScVO4 had been investigated as an alternative red-emitting phosphor under near-ultraviolet excitation. Structural and spectroscopic characterizations were carried out. The results show that the samples can efficiently absorb near-ultraviolet light and produce very bright red emission. In particular, the optimized sample shows much stronger emission intensity than the commercial phosphor Y2O2S: 5% Eu3+ in the excitation range of 365–395 nm, and can reach a strength 5.4 times of the latter under 385 nm excitation. It also has better CIE chromaticity coordinates. These suggest ScVO4: Bi3+, Eu3+ as a promising red-emitting phosphor for white light-emitting diodes based on near-ultraviolet light-emitting diode chips.

Enhanced Optical Properties of Bredigite‐Structure Ca13.7Eu0.3Mg2[SiO4]8 Phosphor: Effective Eu Reduction by La Co‐Doping

A green phosphor, La0.4Ca13.3Eu0.3Mg2Si8O31.6+δN0.4−δ (LaCMSN:Eu2+), was prepared by a solid‐state reaction and an efficient green emission was observed at 506 nm under near‐ultraviolet (NUV) excitation. The structural and optical properties of LaCMSN:Eu2+ phosphors as well as their thermal quenching were investigated. The partial substitution of La3+ and N3− in Ca13.7Eu0.3Mg2Si8O32 led to a considerable enhancement in the peak emission intensity by as much as 194%. This demonstrates not only that the total number of Eu2+ activators increased, but also that the probability of a nonradiative transition between Eu2+ and Eu3+ could be reduced as the increase in concentration of the former is at the expense of the later. The white light‐emitting diode (LED) was fabricated using phosphor with a NUV LED chip. The LED showed warm white light with an excellent color rendering index of 91. The LaCMSN:Eu2+ is thus a potential green‐emitting phosphor for white LEDs.