Ce-Doped La3Si6.5Al1.5N9.5O5.5, a Rare Highly Efficient Blue-Emitting Phosphor at Short Wavelength toward High Color Rendering White LED Application

Development of a novel Eu2+ activated oxonitridosilicate cyan phosphor for enhancing the color quality of a violet-chip-based white LED

Cyan phosphors are urgently needed to fill the cyan gap and improve the spectral continuity of white light-emitting diodes (LEDs) to cater to the high demand for high-quality lighting. Here, a series of new Eu2+-activated La3Si6.5Al1.5N9.5O5.5 (LSANO) cyan phosphors were prepared, and their luminescence properties and color centers were analyzed through fluorescence spectral measurements from 7 K to 475 K. At 300 K, the photoluminescence excitation (PLE) spectrum monitored at 483 nm presents a broadband of 200-460 nm with a peak at 398 nm, matching well with commercial violet LED chips. When excited by 398 nm violet light, the photoluminescence emission (PL) spectrum of LSANO:0.01Eu2+ exhibits a cyan emission band at about 483 nm. At 7 K, the emission spectrum clearly shows an asymmetric emission band and the emission peak wavelength changes from 483 nm (300 K) to 500 nm (7 K), indicating that there are two possible color centers in the LSANO:Eu2+ phosphor. Moreover, the maximum emission value can be adjusted from 480 to 499 nm by adjusting the doping content of Eu2+. Finally, a violet-chip-based white LED with the optimized color quality of Ra = 91.4, Rf = 90.1, and Rg = 93.6 was fabricated by adding the prepared cyan phosphor, verifying the potential application of the prepared cyan phosphor LSANO:Eu2+ in high-quality white LEDs.

Color tuning in Ca3−xMx(PO4)2:Eu2+ (M = Sr, Ba) phosphors via cation substitution

A series of Ca_3−xM_x(PO₄)₂:Eu²⁺ (M = Sr, Ba) phosphors were prepared via a high-temperature solid-state reaction process.

New Deep-Blue-Emitting Ce-Doped A4-mBnC19+2mX29+m (A = Sr, La; B = Li; C = Si, Al; X = O, N; 0 ≤ m ≤ 1; 0 ≤ n ≤ 1) Phosphors for High-Color-Rendering Warm White Light-Emitting Diodes

A new sialon Eu_3.60LiSi_13.78Al_6.03O_6.82N_22.59 has been discovered via the single-particle diagnosis approach. Its crystal structure (space group P3m1) was solved and refined from single-crystal X-ray diffraction data. It has the interesting feature of two types of disorder at the Eu2 site: positional disorder (Eu2a/Eu2b) and substitutional disorder with (Si/Al)₂(O/N). The structure is generalized to the formula A_4-mB_nC_19+2mX_29+m (A = Sr, La, Eu, Ce; B = Li; C = Si, Al; X = O, N; 0 ≤ m ≤ 1; 0 ≤ n ≤ 1), of which Sr_3.61LiSi_14.27Al_5.61O_6.19N_23.25 (Sr-sialon, m = 0.41, n = 1) and La_2.85Sr_0.76LiSi_14.86Al_4.93O_2.89N_26.51 (LaSr-sialon, m = 0.40, n = 1) are two examples that have been obtained as a single-phase powder. Sr-sialon:Eu and LaSr-sialon:Eu both show blue to yellow emission, depending on the Eu concentration, whereas Sr-sialon:1% Ce shows a deep-blue emission band centered at 422 nm with a full width at half-maximum of 80 nm and an internal quantum efficiency of 80% (λ_ex = 355 nm). The latter phosphor has very good thermal stability of both emission intensity and color. A white light-emitting diode (LED) containing the newly discovered Sr-sialon:5% Ce as the blue phosphor component shows excellent color-rendering indices (R_a = 96 and R₁₂ = 97) with a correlated color temperature of 4255 K. This indicates that Sr-sialon:Ce is a highly promising deep-blue phosphor for illumination grade white LEDs.

Highly Efficient and Thermally Stable Blue-Green (Ba0.8Eu0.2O)(Al2O3)4.575×(1+ x) Phosphor through Structural Modification

Exploring phosphors with high quantum efficiency (QE) and thermal stability is an important issue for their application in white light-emitting diodes (LEDs). In this work, the crystal structure and luminescent properties of Eu²⁺-activated aluminate phosphors with a normal composition (Ba_0.8Eu_0.2O)(Al₂O₃)_{4.575×(1+ x)} (short for BA_{1+ x}O:0.2Eu²⁺) were studied. Although the crystal structures of BA_{1+ x}O:0.2Eu²⁺ have a same space group, the increase of the Al content will lead to the decrease of cell volume, occupancy of Ba and O6 that is at around Ba1 site, and the increase of the average distance between Eu²⁺ ions, which are responsible for the modification of luminescent properties. BA_{1+ x}O:0.2Eu²⁺ exhibits a blue-green emission with an emission peak at around 450 nm and a shoulder at around 490 nm. The increase of Al/(BaEu) ratio results in the increase of both absolute QE and thermal stability. The absolute QE of BA_1.5O:0.2Eu²⁺ is 99.4%, and the emission intensity at 150 °C remains more than 90% of that at room temperature, showing the best performance. Furthermore, all of the external QE values of BA_{1+ x}O:0.2Eu²⁺ ( x = 0.2-0.5) are higher than 70%. The properties of the LEDs based on the as-prepared phosphor suggest its potential as a candidate for UV LED pumped phosphor-converted white LEDs.

Preferential Neighboring Substitution-Triggered Full Visible Spectrum Emission in Single-Phased Ca10.5- xMg x(PO4)7:Eu2+ Phosphors for High Color-Rendering White LEDs

Manipulating the distribution of rare-earth activators in multiple cation lattices can achieve versatile color output for single-phased phosphor-converted white light-emitting diodes (LEDs). However, successful cases are barely reported, owing to the uncertain distribution of rare-earth activators and the special combination of three primary colors for white LEDs. Herein, we took whitlockite β-Ca₃(PO₄)₂ as a multiple cation lattice host to manipulate the redistribution of Eu²⁺ activators, and the surprising Mg²⁺-guided redistribution of Eu²⁺ activators among different Ca sites is reported for the first time to regulate the photoluminescence (PL) behavior in series Ca_{10.5- x}Mg _x(PO₄)₇:Eu²⁺ phosphors. The preferential neighboring substitution of smaller Mg²⁺ cations in Ca(5) and Ca(4) sites triggers a discontinuous evolution of local structure along c axis and induces covalent variable Ca(1), Ca(2), and Ca(3) cation sites for the accommodation of Eu²⁺ activators. The unique optical feature enables the single-phased Ca_9.75Mg_0.75(PO₄)₇:Eu²⁺ phosphor-converted white LED to exhibit quite high color-rendering index R_a (85) and R₉ (91) values. The preferential neighboring-cation substitution reported here can not only manipulate the migration of Eu²⁺ activators among different cation sites for tunable PL properties, but also carve out a new way for next-generation high-quality solid-state lighting.

Color tunable emission and energy transfer of Ce3+/Dy3+ codoped Ba3La2(BO3)4 phosphor for UV white LEDs

Polycrystalline Ba₃La₂(BO₃)₄:Ce³⁺,Dy³⁺ sub-micrometer-sized phosphors were synthesized by solid-state reaction under a weak reductive atmosphere. The structure, static and time-resolved photoluminescence are investigated. Under the near-ultraviolet excitation, the Ba₃La₂(BO₃)₄:Dy³⁺ phosphors emit white light with three intense emission bands centered at 483, 575, and 665 nm. The efficient energy transfer from Ce³⁺ to Dy³⁺ in Ba₃La₂(BO₃)₄ phosphor was found by excitation/emission spectra and decay time measurements, and the resonant type was demonstrated by a dipole-dipole mechanism. A tunable emission hue from blue (0.18, 0.20) to blue-white (0.26, 0.29) and eventually to white (0.32, 0.33) was obtained in Ba₃La₂(BO₃)₄:Ce³⁺,Dy³⁺ phosphors. Owing to the broad UV excitation band, indicating that Ba₃La₂(BO₃)₄:Ce³⁺,Dy³⁺ phosphors can be considered as a potential candidate for ultraviolet-based white light-emitting diodes.

Control of the photoluminescence in Ba0.97Y2Si3O10:Eu2+ phosphors via the intensification effect of the second luminescence centre

A method is reported that broadens the FWHMs of the emission spectra of Ba_0.97Y₂Si₃O₁₀:0.03Eu²⁺ by intensifying the second emission peak.

Significantly enhanced photoluminescence and thermal stability of La3Si8N11O4:Ce3+,Tb3+via the Ce3+ → Tb3+ energy transfer: a blue-green phosphor for ultraviolet LEDs

The peak emission intensity and thermal stability of Tb³⁺ in codoped La₃Si₈N₁₁O₄:Ce,Tb sample are strongly enhanced via Ce³⁺ to Tb³⁺ energy transfer.