A series of Eu 2+ -and Mn 2+ -coactivated CaAl 2 Si 2 O 8 phosphors have been synthesized at 1400 °C under a reduced atmosphere and their luminescence properties have been investigated as a function of activator and coactivator concentrations. We have discovered that energy transfers from Eu 2+ to Mn 2+ by directly observing significant overlap of the excitation spectrum of Mn 2+ and the emission spectrum of Eu 2+ as well as the systematic relative decline and growth of emission bands of Eu 2+ and Mn 2+ , respectively. The critical distance and average separation of Eu 2+ and Mn 2+ have also been calculated. By utilizing the principle of energy transfer, we have also demonstrated that with appropriate tuning of activator content CaAl 2 Si 2 O 8 :Eu 2+ ,Mn 2+ phosphors exhibit great potential to act as a phosphor for white-light ultraviolet light-emitting diodes (UVLEDs).
A novel single-composition white-emitting phosphor Ca3Y(GaO)3(BO3)4:Ce3+,Mn2+,Tb3+ has been synthesized by a high-temperature solid-state reaction. The spectral overlap between the emission band of Ce3+ and the excitation band of Mn2+, which supports the occurrence of the energy transfer from Ce3+ to Mn2+, has been studied and demonstrated to be a resonant type via a dipole−quadrupole mechanism. Because there was no spectral overlap between the emission spectra of Ce3+ and excitation band of Tb3+ in our study, no energy transfer from Ce3+ to Tb3+ was observed, indicating that Ce3+ and Tb3+ were coexcited. Through effective resonance-type energy transfer and coexcitation, the chromaticity coordinates of Ca3Y(GaO)3(BO3)4:Ce3+,Mn2+,Tb3+ phosphors can be tuned from (0.152, 0.061) for Ca3Y(GaO)3(BO3)4:Ce3+ to (0.562, 0.408) for Ca3Y(GaO)3(BO3)4:Mn2+, and eventually reaching (0.314, 0.573) for Ca3Y(GaO)3(BO3)4:Tb3+. A white light-emitting diode (LED) was fabricated by using the white-emitting single-composition (Ca0.97)3(Y0.92)(GaO)3(BO3)4:0.01Ce3+,0.03Mn2+,0.07Tb3+ pumped by a 365 nm UV-chip. Our results indicated that the CIE chromaticity coordinates and correlated color temperature (CCT) for white UV-LEDs were (0.31, 0.33) and 6524 K, respectively. Therefore, our novel white Ca3Y(GaO)3(BO3)4:Ce3+,Mn2+,Tb3+ can serve as a key material for phosphor-converted white-light UV-LEDs.
Colloidal quantum dots which can emit red, green, and blue colors are incorporated with a micro-LED array to demonstrate a feasible choice for future display technology. The pitch of the micro-LED array is 40 μm, which is sufficient for high-resolution screen applications. The method that was used to spray the quantum dots in such tight space is called Aerosol Jet technology which uses atomizer and gas flow control to obtain uniform and controlled narrow spots. The ultra-violet LEDs are used in the array to excite the red, green and blue quantum dots on the top surface. To increase the utilization of the UV photons, a layer of distributed Bragg reflector was laid down on the device to reflect most of the leaked UV photons back to the quantum dot layers. With this mechanism, the enhanced luminous flux is 194% (blue), 173% (green) and 183% (red) more than that of the samples without the reflector. The luminous efficacy of radiation (LER) was measured under various currents and a value of 165 lm/Watt was recorded.
We have prepared and characterized a series of substituted 2-phenylbenzthiazole (4-CF3,
4-Me, 4-OMe, 4-F, 4-CN, and 3-F) ligands. The intermediate di-irrido and the six-coordinated
mononuclear iridium(III) dopants of the above ligands have been synthesized and characterized. These complexes are thermally stable between 275 and 300 °C depending upon the
types and volatility of substituents. They emit bright yellow to orange light. The peak
emission wavelengths of the dopants can be finely tuned depending upon the electronic
properties of the substituents as well as their positions in the ring. In the absorption spectra,
the 1MLCT and 3MLCT transitions have been resolved in the range of 385−450 nm. The
long tail toward lower energies are assigned to 3MLCT and 3π−π* transitions, which gains
intensity by mixing with the higher lying 1MLCT state through the spin−orbit coupling of
iridium(III). All complexes exhibit one electron oxidation and the oxidation potential values
can be correlated with the Hammett substituent constants. The electroluminescent
characteristics for the substituted and the unsubstituted complexes have been compared
and discussed.
The SrZn2(PO4)2:Eu2+,Mn2+ phosphor shows two emission bands under ultraviolet radiation; the one observed at 416nm is attributed to Eu2+ occupying the Sr2+ sites and the other asymmetric band deconvoluted into two peaks was found to center at 538 and 613nm, which originate from Mn2+ occupying two different Zn2+ sites. The energy transfer from Eu2+ to Mn2+ has been demonstrated to be a resonant type via a dipole-quadrupole mechanism. By utilizing the principle of energy transfer and appropriate tuning of activator contents, we have demonstrated that SrZn2(PO4)2:Eu2+,Mn2+ is potentially useful as an ultraviolet-convertible phosphor for white-light emitting diodes.
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