Vacancies Substitution Tuning Photoluminescence and Distortion Triggered Eu Migration in NASICON-Type Phosphors

Abstract

Phosphor-converted white light-emitting diodes (PC-WLEDs) are an energy-saving alternative to traditional light sources, for which efficient and thermal stable phosphors are in h i g h d e m a n d . H e r e , t h e N A S I C O N -t y p e Na 3+x □ 1−x Sc 2−x Mg x (PO 4 ) 3 :Eu 2+ (N□SM x PO:Eu 2+ ) phosphor is synthesized for Na vacancies repair. The photoluminescence quantum yield (PLQY) and the emission morphology of solid solution are dramatically affected by the composition, with the PLQY improving by 27% and the emission spectra red-shifting by 11 nm going from x = 0.0 to x = 0.3. These highlights likely stem from the enhanced structural rigidity and the distortion of NaO 6(8) polyhedra, respectively. Temperature-dependent emission spectra reveal the thermal stable luminescence of the series. A luminescence intensity of ≥90% relative to the room-temperature value is observed at 425 K. The LED device with the blending of N□SM 0.3 PO:Eu 2+ and commercial components generates CRI (colorrending indices) = 88 and CCT (correlated color temperatures) = 5209 K, characteristic of high-quality white light. More interestingly, the distortion of crystal lattice could switch to the migration of Eu ion to (Sc/Mg) site at x = 0.4. The phenomenon leads to the oxidation of Eu 2+ , optically rapidly weakening the photoluminescence. Modifying the lattice distortion in some type phosphors may be a very useful approach to improve the efficiency of luminescence materials.

A highly efficient UV-to-red-light conversion by LuNbO4:Eu3+ phosphors through exciton-assisted host-activator energy transfer

“…Based on the measured PL spectra, the chromaticity coordinate temperature (CCT) and the color purity (CP) were calculated by the following formulas. [14][15][16][17] CCT = À437n 3 + 3601n 2 À 6861n + 5514. 31 (1)…”

“…2,5 Phosphors doped with trivalent europium (Eu 3+ ) ions are promising candidates for UV-to-red WCMs, since the Eu 3+ ions can emit intense red luminescence based on the 4f-4f transitions as incorporated in a proper ligand field. [6][7][8][9][10][11][12][13][14][15][16][17][18] For example, a Eu 3+ luminophore with a photosensitizer (hexafluoroacetylacetonato: hfa) and a stabilizer (triphenylphosphine oxide: TPPO), Eu(hfa) 3 (TPPO) 2 , emits red luminescence with an emission quantum yield (QY) of 70% under UV light irradiation and has been used as a WCM to boost plant growth. 2,6,7 The Eu 3+ ions in organic ligand compounds are excited by energy transfer from the organic ligands, which are able to absorb UV light in a broad spectral region and give out red light with high purity.…”

“…In these materials, the broad-band UV excitation is due to a charge-transfer transition, and the sharp red emission at around 615 nm was demonstrated by an electric dipole transition of 5 D 0 -7 F 2 of Eu 3+ ions at asymmetric lattice sites. [14][15][16][17][18] Although the emission QY could reach 69% for YVO 4 :Eu 3+ /Bi 3+ exposed to UV light, 4,13 further improvement of the luminescent efficiency by traditional methods is still quite limited and challenging for real applications.…”

Crystal Field Engineering Yields New 3D Layered Solid Solution Phosphors (Ca/Sr)4MgAl2Si3O14:Eu2+ for White-Light-Emitting Diode Full-Spectrum Lighting

“…They are widely recognized and rapidly becoming the preferred choice in the lighting market due to their energy-saving, eco-friendly, and highly efficient characteristics. − These advantages have led to successful applications of WLEDs in various fields, such as indoor lighting and backlight displays. − The basic principle of WLEDs revolves around the production of white light through the excitation of one or more phosphors by using UV or blue chips. This principle enables the generation of high-quality, white light with enhanced energy efficiency and environmental friendliness. − After decades of development, the process technology for WLEDs has indeed matured significantly. Currently, the commercial method for obtaining white light involves coating a green-emitting phosphor and a red phosphor onto a blue chip.…”

Correlated Na+ Ion Migration Invokes Zero Thermal Quenching in a Sodium Superionic Conductor-type Phosphor

“…Furthermore, a zero-TQ phosphor exhibits a relatively low photoluminescence (PL) quantum yield (PL QY), which is crucial for improving its PL QY for further applications. Therefore, many research groups have attempted various strategies, such as aliovalent and isovalent doping at Na and Sc sites, to enhance the PL QY with zero-TQ properties. − However, aliovalent doping in NSPO:Eu 2+ improves the PL QY but cannot sustain the zero-TQ property at elevated temperatures. Enhancing the emission efficiency along with the zero-TQ property is challenging because these two properties are inversely proportional to each other.…”