current backlit field of liquid-crystal display (LCD). [2] To date, β-SiAlON:Eu 2+ phosphor is still considered as the optimum green component for the commercial LCD backlights owing to its green emission at ≈540 nm with full width at half maximum (FWHM) of 55 nm, internal quantum efficiency of 52.2%, external quantum efficiency of 38.4%, and thermal stability of 12% emission loss at 423 K. [3] Whereas, its emission band is not narrow enough and the peak position is dissatisfactory to realize wider CG. The synthesis condition is not sufficiently facile in reducing the cost compared with oxide. Consequently, discovering stable narrow-band green emitters suitable for blue LED chip excitation is crucial to improve the CG of the phosphor-converted backlighting device.Transition metal Mn has been widely explored in various optical materials such as the Mn-activated phosphors, quantum dots (QDs) and metal halides perovskite. [4][5][6] Different spectral profiles can be generated by Mn 2+ -doped compounds owing to the d-d parity forbidden transitions of Mn 2+ ions, which are strongly influenced by the crystal field. Generally, a typical green emission will appear when Mn 2+ is surrounded by four ligands with lower ligand field strength. [6] For the current green emitters based on Mn 2+ , the emission band is characterized by a FWHM below 54 nm and can be as narrow as 26 nm. [7] The presence of Mn 2+ ions in metal halide perovskites can bring forth new optical features, improve the thermal and air stability, and enhance photoluminescence quantum yield. [7a,8] However, although the Mn 2+ -based nanocrystal or bulk-crystal metal halide perovskites reduces the toxicity of the lead elements, the emission bands of these materials have been greatly broadened compared with the CsPbBr 3 and CH 3 NH 3 PbBr 3 QDs. This leads to the reduced color purity and thus restricts its commercial applications in wide color gamut LCD backlights. Moreover, fatal problems, such as high susceptibility to moisture, heat, and light for these materials continue because of the poor chemical and structural stability. Under the circumstances, the Mn 2+ -activated phosphors reveal their sufficient preponderance in achieving desirable green emission with ultra-narrow band and prominent stability for display technology. The commercial green phosphors Zn 2 SiO 4 :Mn 2+ and BaAl 12 O 19 :Mn 2+ were widely used for PDPs in the long past. [9] Some newly emerging Mn 2+ -activated Narrow-band green-emitting phosphors have attracted increasing attention for designing wide color gamut devices with high quality. However, the development of highly efficient and thermally stable green phosphor with narrow band is still a significant challenge. Herein, a novel green narrow-band phosphor, BaZnAl 10 O 17 :Mn 2+ (BZAO:Mn 2+ ) is developed owing to the weak coupling interaction of Mn ions in the highly symmetric BZAO with rigid structure. Upon 450 nm excitation, BZAO:0.20Mn 2+ shows an intense green emission peaking at 516 nm with a full width at half maximum of 3...
Full visible emission achieved by a single-phased system is of great interest to researchers for the development of high-quality solid-state lighting devices. Herein, novel Eu 2+ and Mn 2+ co-doped (1 − x)β-Ca 3 (PO 4 ) 2 -xCa 9 La(PO 4 ) 7 solid solution phosphors are designed to realize single-phased white light emission. The effects of variational x on lattice structure, color-tunable emission, thermal stability, and energytransfer efficiency from Eu 2+ to Mn 2+ are systematically investigated. Tunable color emissions are achieved by manipulating the redistributions of Eu 2+ ions among the different cationic sites under the influence of generated empty site in the M(4) site. Meanwhile, the changes of critical distances among the Eu 2+ and Mn 2+ caused by the variational x results in the changes of energy-transfer efficiency from different Eu 2+ luminescent centers to Mn 2+ due to the existence of structural confinement effect. The calculated results indicate that Eu1−Mn and Eu2−Mn possess higher energy-transfer efficiencies than other Eu−Mn pairs. Under the combined influence of the two effects, single-phased full visible white emission covering from 400 to 700 nm has been realized via the adjustment of solid solution, which makes the fabricated white-light-emitting diode (WLED) possess high color-rendering index (86.9) and R9 (87.2) as well as low correlated color temperature (3947 K). The results show that the 0.2β-Ca 3 (PO 4 ) 2 -0.8Ca 9 La(PO 4 ) 7 :0.01Eu 2+ , 0.20Mn 2+ could act as a promising phosphor for single-phased WLEDs. This work will open up a new avenue for tuning the multiple activator sites and energy-transfer efficiencies simultaneously to realize single-phased full visible white emission.
This work shows a useful method to design new green phosphors with ultra-narrow emission bands effectively via managing the energy-transfer efficiency from Ce3+ to Tb3+ ions in perfectly matched inorganic compounds.
We propose and experimentally demonstrate a silicon integrated high-order mode fiber-chip coupler. By utilizing a structure of apodized double-part gratings with mode selective trident, TE1 mode can be coupled with low mode crosstalk. Design details and the corresponding simulation results are presented. The coupler is fabricated on silicon integrated platform. Measured results show the loss is 4.68 dB for TE1-LP11 mode coupling with the mode crosstalk <-23dB. The proposed coupler could be utilized in the advanced mode division multiplexing (MDM) system.
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