Transition metal ion co-doped MgO–MgF2-GeO2:Mn4+ red phosphors for white LEDs with wider color reproduction gamut

Self‐Activated Tungstate Phosphor for Near‐Infrared Light‐Emitting Diodes

“…Figure 1b depicts the crystal structure of the NaLaMgWO 6 crystal structure and the coordination environment of Na + , La 3+ , Mg 2+ , and W 6+ cations. Notably, NaLaMgWO 6 is monoclinic with a space group of C12/m1 (12) ] via shared edges to form alternating layers. [9a,25] In addition, the phosphors prepared by the high-temperature solid-state reaction method usually have irregular grain particles, where a smooth surface with a uniform irregular shape and a particle size between 100 and 800 nm were observed (Figure 1c-d).…”

Unveiling the luminescence property of Li2MgGeO4:Mn4+ featuring the tetrahedral crystallographic-site occupancy of Mn4+

“…4c. In contrast to the invariant ground state of Mn 4+ in octahedral occupancy, that for Mn 4+ in tetrahedral occupancy is crystal field dependent, i.e., under a weak crystal field, it is assigned to 4 T 1 , but it changes to 2 E under a strong crystal field. By finding the energy ratio of the E-band in PLE to the peak in PL (i.e.…”

“…Mn 4+ -activated oxide phosphors generally exhibit high chemical stability and strong red to deep red luminescence under ultraviolet (UV) light excitation, and they can be prepared using cheap starting materials via eco-friendly processes. Hence, these phosphors are very popular candidates for applications requiring red light and hence have been investigated for warm white-light emission and wide-gamut backlighting based on phosphor-converted white light-emitting diodes ( pc-WLEDs) [1][2][3][4][5][6] as well as for indoor plant cultivation 7,8 and thermometry. 3,9 As is well known, under a crystal field environment with an O h symmetry, the five d orbitals in a transition metal (TM) ion split into three-fold t 2g and two-fold e g levels.…”

“…Depending on both the TM ion and the surrounding crystal field, specific absorption and emission due to electronic transitions between the d-splitted electronic levels can often be observed. In terms of Mn 4+ ions (3d 3 configuration) under the octahedral crystal field, the three degenerated t 2g levels with one electron occupancy in each (the spectroscopic term is 4 F in the ground state of free Mn 4+ ions) can split into three levels of 4 A 2g , 4 T 1g and 4 T 2g , with 4 A 2g being the lowest level. From these phosphors, absorption with a wide band in both UV (250 to 400 nm) and blue-green (400 to 500 nm) regions, as well as narrow-band red emissions at 600 to 740 nm wavelengths, can be typically observed, 2,3,10 and usually, the absorption originates from the allowed electronic transition of 4 A 2g → ( 4 T 1g and 4 T 2g ), and the emission is assigned to spinforbidden 2 E g (from e g of empty 3d in octahedral-sited Mn 4+ ) → 4 A 2g transition.…”

“…In terms of Mn 4+ ions (3d 3 configuration) under the octahedral crystal field, the three degenerated t 2g levels with one electron occupancy in each (the spectroscopic term is 4 F in the ground state of free Mn 4+ ions) can split into three levels of 4 A 2g , 4 T 1g and 4 T 2g , with 4 A 2g being the lowest level. From these phosphors, absorption with a wide band in both UV (250 to 400 nm) and blue-green (400 to 500 nm) regions, as well as narrow-band red emissions at 600 to 740 nm wavelengths, can be typically observed, 2,3,10 and usually, the absorption originates from the allowed electronic transition of 4 A 2g → ( 4 T 1g and 4 T 2g ), and the emission is assigned to spinforbidden 2 E g (from e g of empty 3d in octahedral-sited Mn 4+ ) → 4 A 2g transition. [11][12][13] It has been found that in these phosphors, the energy of absorption is much dependent on the strength of the crystal field, whereas the emission energy is slightly influenced but associated with the bond hybridization between Mn 4+ and the ligand oxygen, i.e., the nephelauxetic effect.…”