Chemical stabilization of Eu2+ in LuPO4 and YPO4 hosts and its peculiar sharp line luminescence

Mixed Microscopic Eu2+ Occupancies in the Next‐Generation Red LED Phosphor Sr[Li2Al2O2N2]:Eu2+ (SALON:Eu2+)

“…This implies strong Eu 2+ ‐ligand bonds, as was also recently found in the structurally related oxidosilicates with Eu 2+ in the smaller cation channels containing Li + ions that give rise to a green luminescence with similar vibronic fine structure at 10 K. From the intensity ratio of the 0′ → 1 and 0′ → 0 vibronic line, it can be derived that the Huang‐Rhys‐Pekar parameter S must be around 1.4 being very small. Only few examples such as RE PO 4 :Eu 2+ , Zr 4+ ( RE = Y, Lu) [ 21 ] or selected perovskite‐derived hydrides and deuterides [ 22 ] are known to give rise to 4f 6 5d 1 → 4f 7 ‐based luminescence with even smaller Huang‐Rhys‐Pekar factors ( S < 1). Thus, the Eu‐ligand equilibrium bond length in the lowest excited emissive 4f 6 5d 1 state and the 4f 7 ( 8 S 7/2 ) ground level is very similar and barely changes.…”

Eu2+Stabilized at Octahedrally Coordinated Ln3+Site Enabling Red Emission in Sr3LnAl2O7.5(Ln = Y or Lu) Phosphors

“…The PL blue shift for Sr 3 YAl 2 O 7.5 :Eu, due to the Eu 2+ at the Y 3+ site, suffers an insignificant centroid shift, and the crystal‐field splitting, due to Y 3+ , has a larger ion radius than that of Lu 3+ (IR = 0.86 Å for CN = 6). [ 10 ] The slightly narrower emission and smaller Stokes shift for Sr 3 YAl 2 O 7.5 :Eu are related to the more restricted structural relaxation for Eu 2+ on the larger Y 3+ site. [ 16–17 ] Identical emission behaviors were found in our previously studied narrow‐band MBe 2 (PO 4 ) 2 :Eu 2+ (M = Ca, Sr) phosphors, wherein Eu 2+ is located at the larger Sr 2+ site, showing narrower emission, smaller Stokes shift, and higher emission energy as compared to that of Eu 2+ at the Ca 2+ site.…”

“…recently reported the chemical stabilization of Eu 2+ at the Ln 3+ site in orthophosphates LnPO 4 (Ln = Y or Lu) by introducing Hf 4+ as a charge compensator. [ 10 ] These results are impressive as Ln 3+ has a small ionic radius, as a consequence short LnO bond length is generally formed, and strong covalency and crystal field strength are expected once Eu 2+ is substituted at the Ln 3+ site. Recently discovered Rb 3 YSi 2 O 7 :Eu 2+ , K 3 YSi 2 O 7 :Eu 2+ , and K 3 LuSi 2 O 7 :Eu 2+ phosphors by our group could further support this, with red emission originating from Eu 2+ at the Y 3+ and Lu 3+ sites, respectively.…”

Chasing Down the Eu2+ Ions: The Delicate Structure−Property Relationships in the Ultra‐Narrow Band Phosphor K1.6Na2.1Li0.3[Li3SiO4]4:Eu2+

“…[ 56,58,59 ] It should be noted, however, that the observation of an additional vibronic side feature at 490 nm implies a strong zero‐phonon line at 486 nm. In the context of this interpretation, the observed fwhm of 155 cm −1 is still high compared to the usually observed very sharp vibronic lines as reported in, for example, MgF 2 :Eu 2+[ 91 ] or REPO 4 :Eu 2+ (RE = Y, Lu), [ 92 ] which can be ascribed to the mixed occupancy at the K2/Na2 site.…”