NUV-pumped red-emitting Ca9MnK(PO4)7 phosphor: energy transfer and charge compensation

The development of novel Mn-based phosphor hosts has received increasing interest in the search for highly efficient red emitting phosphors for white LED applications. In this study, Ca₉MnK(PO₄)₇, a compound with the β-Ca₃(PO₄)₂-type structure, was successfully synthesized by a high-temperature solid-state reaction process. The Eu²⁺-doped Ca₉MnK(PO₄)₇ phosphor exhibits a broadband red emission peaking at 650 nm. The optimal excitation wavelength is 395 nm, which matches that of commercial ultraviolet (NUV) chips. Codoping Ce³⁺ ions into the Ca₉MnK(PO₄)₇:Eu²⁺ phosphor efficiently improves Mn²⁺ luminescence. Here, Ce³⁺ acts as a charge compensator rather than a sensitizer and substantially increases the effective number of Eu²⁺ and finally improves the red emission of Mn²⁺. The charge compensation mechanism is also verified by codoping some optically inert rare earth ions (Ln³⁺) including Y³⁺, La³⁺ and Gd³⁺. The results demonstrate that these developed Ca₉MnK(PO₄)₇:Eu²⁺, Ln³⁺ phosphors have great potential for application in NUV-based white LEDs. The energy transfer approach combined with the charge compensation technique is valuable for improving the performance of the red-emitting Ca₉MnK(PO₄)₇:Eu²⁺ phosphor, which can further be used in developing other Mn-based phosphors.

Multiobjective Machine Learning-Assisted Discovery of a Novel Cyan-Green Garnet: Ce Phosphors with Excellent Thermal Stability

Ce-doped garnet phosphors play an important role in the white light-emitting diode (LED) family. In the past years, a lot of trial-and-error experiments guided by experience to discover phosphors suitable for white LEDs have been presented. The working temperature of phosphors may reach 200 °C in white LEDs, and so, the exploration of phosphors with excellent thermal stability at the desired wavelength continues to be a challenge. In the present study, to discover novel cyan-green garnet:Ce phosphors, wavelength and thermal stability machine learning models were built by constructing reasonable features. Among the 171,636 compounds with garnet structures predicted by our models, 25 samples were selected for preparation and characterization by multiobjective optimization based on active learning. Lu_1.5Sr_1.5Al_3.5Si_1.5O₁₂:Ce performed the best with excellent thermal stability (≥60% emission intensity was retained at 640 K) and exhibited emission peaks of about 505 nm, and it is a very promising phosphor for future applications, especially in high-temperature operating environments.

Eu2+ Doping Concentration-Induced Site-Selective Occupation and Photoluminescence Tuning in KSrScSi2O7:Eu2+ Phosphor

Regulation of Eu²⁺ dopants in different cation sites of solid-state materials is of great significance for designing multicolor phosphors for light-emitting diodes (LEDs). Herein, we report the selective occupation of Eu²⁺ for multiple cationic sites in KSrScSi₂O₇, and the tunable photoluminescence from blue to cyan is realized through Eu²⁺ doping concentration-dependent crystal-site engineering. Eu²⁺ preferably occupies the K and Sr sites in KSrScSi₂O₇ at a low doping concentration, resulting in a 440 nm blue emission. As the Eu²⁺ concentration increases, a new Eu²⁺ substitution pathway is triggered, that is, Eu²⁺ enters the Sc site, leading to the red-shifted emission spectra from 440 to 485 nm. The doping mechanism and photoluminescence properties are corroborated by structural analysis, optical spectroscopy study, and density functional theory calculations. The optical properties of the as-fabricated white LEDs are studied, which demonstrates that these phosphors can be applied to full-spectrum phosphor-converted LEDs. This study provides a new design strategy to guide the development of multicolor Eu²⁺-doped oxide phosphors for lighting applications.

The direct identification of quantum cutting in Tm3+ ions and energy transfer in the Tm3+/Yb3+ system based on a Ba2Gd2Si4O13 oxide host

Quantum cutting (QC) is an important physical process, the occurrence of which still needs further verification in different luminescent ions.

Two-Site Occupancy Induced the Broad-Band Emission in Ba4-x-ySryLa6O(SiO4)6:xEu2+ Phosphor for White LED and Anti-counterfeiting

With the increasing demand for new inorganic functional materials, more and more attention is paid to rare earth ions doped luminescent materials. In this work, Eu2+ doped Ba4La6O(SiO4)6 phosphor was...

A new broadband near-infrared phosphor emitting Mg2Al4Si5O18:Cr3+ for night-vision imaging

Phosphor-converted light-emitting diodes (pc-LEDs) have important applications in security surveillance and food testing, however, developing new broadband near-infrared phosphors remains an important issue. Herein, the high-temperature solid-state reaction method was...

Bi3+ photoluminescence in Y1-xBixCa3(GaO)3(BO3)4 and energy transfer to Eu3+ and Tb3+ in co-doped phosphors

Bi³⁺ possesses outer shell lone pair electrons, and, thus the so-involved photoluminescence (PL) is sensitive to the surrounding coordination. Besides, the similarity in the structural chemistry between Bi³⁺ and rare earth (RE) ions inspires us to investigate the Bi³⁺-PL performance in RE³⁺-containing hosts. Herein, Y_1-xBi_xCa₃(GaO)₃(BO₃)₄ (0.01 ≤ x ≤ 0.15) compounds were prepared by a high temperature solid state reaction method. The successful cationic doping and phase purity were confirmed by powder X-ray diffraction analysis. This series of phosphors exhibit the very strong absorption of Bi^{3+ 1}S₀ → ³P₁ at 272 nm along with the intense blue emission with a maximum at 399 nm and a full width at half maximum (FWHM) of 59 nm. They retained 78.86% of the emission intensity at 150 °C, with reference to that at room temperature. Moreover, Bi³⁺ could also behave as a sensitizer to enhance the emission efficiency of RE³⁺ and thus to realize color-tunable phosphors. The energy transfer was proved in the co-doped phosphors Y_0.95-yBi_0.05Eu_yCa₃(GaO)₃(BO₃)₄ (0.05 ≤ y ≤ 0.6) and Y_0.95-zBi_0.05Tb_zCa₃(GaO)₃(BO₃)₄ (0.05 ≤ z ≤ 0.6), and color-tunable emissions from blue to red, or from blue to green were realized in these two series of phosphors.

Novel narrow-band blue light-emitting phosphor of Eu2+-activated silicate used for WLEDs

Owing to the broad application scope of phosphors for light and display, the development of narrow-band light-emitting phosphors has recently gained considerable research attention. In this study, a new type of narrow-band blue light-emitting phosphor, Rb₂HfSi₃O₉:Eu²⁺, with a full width at half maximum (FWHM) of 64 nm was synthesized successfully. Upon the near visible ultraviolet (NUV) light excitation, the internal quantum efficiency of Rb₂HfSi₃O₉:Eu²⁺ was 68%. It also exhibited good thermal stability, which was higher than that of a commercial blue phosphor (BaMgAl₁₀O₁₇:Eu²⁺) at 150 °C. The significant photoluminescence properties of Rb₂HfSi₃O₉:Eu²⁺ were found to be related to its robust crystal structure, which was investigated in detail. The results indicate that Eu²⁺-activated Rb₂HfSi₃O₉ is a promising phosphor for use in white light-emitting diodes.

Enhanced luminescence and tunable color in [Eu2+, Si4+]/Mn2+ doped K2BaCa(PO4)2 based on charge compensation and energy transfer

Recently, using the Eu2+ → Mn2+ energy transfer strategy to explore new single-phase phosphors suitable for the near-ultraviolet (n-UV) region has become one of the major strategies in solid-state lighting applications. Therefore, a novel color-tunable K2BaCa(PO4)2 (KBCPO):[Eu2+,Si4+],Mn2+ phosphor was developed because of the preeminent thermal stability of luminescence of Eu2+-activated KBCPO. In this study, we first designed a [Eu2+, Si4+] → [K+, P5+] charge compensation strategy to optimize the luminescence properties of Eu2+ in the KBCPO matrix. In terms of the obtained KBCPO:[Eu2+,Si4+] phosphor, this charge compensation method on the one hand strengthens the emission of Eu2+, and on the other hand, it dramatically improves the thermal stability of luminescence. In particular, the emission intensity of the KBCPO:0.03[Eu2+,Si4+] sample at 548 K can reach 103% relative to that at the initial temperature of 298 K. Based on this charge compensation strategy, we finally obtained a new dual emission KBCPO:[Eu2+,Si4+],Mn2+ phosphor. The analysis of the luminescence properties indicates that the emission enhancement of Mn2+ in KBCPO:[Eu2+,Si4+],Mn2+ stems from the energy transfer of Eu2+ → Mn2+ with the mechanism of the electric dipole-dipole interaction when excited at 365 nm. In addition, KBCPO:[Eu2+,Si4+],Mn2+ also has excellent thermal stability and the emission color could be easily tuned from cyan to orange only by adjusting the Eu2+ doping level. These results confirm that the KBCPO:[Eu2+,Si4+],Mn2+ phosphor is a viable candidate for n-UV white light emitting diodes.

Energy transfer, multi-colour emission and high thermal stability behaviour of K2Tb1−xEuxHf(PO4)3 with langbeinite-type structure

This study provides a new series of solid solution phosphors, K₂Tb_1−xEu_xHf(PO₄)₃, with multi-color emission evolution and high thermal stability for LED lamps.

Preparation and Luminescence Properties of Ba₅Si₈O21 Long Persistent Phosphors Doped with Rare-Earth Elements

The phosphors of formula Ba₅Si₈O₂₁:Eu²⁺,Dy³⁺ were synthesized and studied in order to improve their properties. Their synthesis conditions were evaluated as a function of precursors, crucible composition, flux agents, dopants and temperatures. The samples were characterised by means of a systematic investigation through elemental, kinetic, mineralogical (both qualitative and quantitative), and morphological analysis. This study allows for a careful evaluation of the parameters that influence the formation and properties of Ba₅Si₈O₂₁:Eu²⁺,Dy³⁺ phosphors. As for the synthesis conditions, the use of Na₂SiO₃, BaCO₃ and NH₄Cl as precursors was very important to reduce the temperature and time of synthesis. The reducing atmosphere produced with purified coal was cheaper and gave results similar to the more traditional gas mixture (H₂/N₂). At the end of this study, a phosphor with improved long persistent phosphorescence (LPP) characteristics was obtained with Ba/Si = 0.7, Eu/Si = 2.8 × 10⁻³ and Dy/Si = 3.6 × 10⁻³ following a 6 h-synthesis in a quartz crucible.

Microwave-assisted sintering synthesis of greenish-yellow emitting Sr2 SiO4 :Eu2+ phosphors

Europium ion (Eu²⁺ ) doped Sr₂ SiO₄ phosphors with greenish-yellow emission were synthesized using microwave-assisted sintering. The phase structure and photoluminescence (PL) properties of the obtained phosphor samples were investigated. The PL excitation spectra of the Sr₂ SiO₄ :Eu²⁺ phosphors exhibited a broad band in the range of 260 nm to 485 nm with a maximum at 361 nm attributed to the 5f-4d allowed transition of the Eu²⁺ ions. Under an excitation at 361 nm, the Sr₂ SiO₄ :Eu²⁺ phosphor exhibited a greenish-yellow emission peak at 541 nm with an International-Commission-on-Illumination (CIE) chromaticity of (0.3064, 0.4772). The results suggest that the microwave-assisted sintering method is promising for the synthesis of phosphors owing to the decreased sintering time without the use of additional reductive agents.

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.

A strategy for realizing tunable luminescence and full-color emission in Sr3Gd2(Si3O9)2:Eu phosphors by introducing dual functional Mn2+

The introduced Mn²⁺ ion can act as both an activator and a structure regulator in the SGSO:Eu system to achieve full-color emission and tunable luminescence of SGSO:0.03Eu,Mn phosphors.

Morphology and phase transformation from NaCaSiO3OH to Na2Ca2Si2O7 and photoluminescence evolution via Eu3+/Tb3+ doping

The morphologies were in situ constructed from NaCaSiO₃OH to Na₂Ca₂Si₂O₇, and the dependence of their photoluminescence tuning on the Tb³⁺/Eu³⁺ ratio has been discussed.