Red phosphor materials play a key role in improving the lighting and backlit display quality of phosphor-converted white light-emitting diodes (pc-WLEDs). However, the development of a red phosphor with simultaneous high efficiency, excellent thermal stability and high colour purity is still a challenge. In this work, unique non-concentration quenching in solid-solution Cs3Gd1 − xGe3O9:xEu3+ (CGGO:xEu3+) (x = 0.1–1.0) phosphors is successfully developed to achieve a highly efficient red-emitting Cs3EuGe3O9 (CEGO) phosphor. Under the optimal 464 nm blue light excitation, CEGO shows a strong red emission at 611 nm with a high colour purity of 95.07% and a high internal quantum efficiency of 94%. Impressively, this red-emitting CEGO phosphor exhibits a better thermal stability at higher temperatures (175–250 °C, >90%) than typical red K2SiF6:Mn4+ and Y2O3:Eu3+ phosphors, and has a remarkable volumetric negative thermal expansion (coefficient of thermal expansion, α = −5.06 × 10−5/°C, 25–250 °C). By employing this red CEGO phosphor, a fabricated pc-WLED emits warm white light with colour coordinates (0.364, 0.383), a high colour rendering index (CRI = 89.7), and a low colour coordinate temperature (CCT = 4508 K). These results indicate that this highly efficient red-emitting phosphor has great potential as a red component for pc-WLEDs, opening a new perspective for developing new phosphor materials. A luminescent material that undergoes an unusual heat-shrinking process shows promise for enhancing the efficiency of white light-emitting diodes (LEDs). Current technologies for generating white LEDs often combine near-ultraviolet light with background radiation from red, green, and blue phosphors. J.L. from China’s Changchun Institute of Applied Chemistry and colleagues have now developed a red phosphor that remains active at temperatures which shut down other red-light emitters. The team’s compound, a cesium-based metal oxide doped with rare earth ions, has a crystal structure that contracts upon heating and avoids symmetry-distorting effects associated with thermal quenching. This unique structure also supports higher dopant concentrations than typical phosphors for improved colour rendering in prototype white LEDs. A highly efficient red-emitting Cs3EuGe3O9 phosphor for high-performance pc-WLEDs is discovered with non-concentration quenching, favourable thermal stability, high colour purity and negative thermal expansion.

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Thermally stable and highly efficient red-emitting Eu3+-doped Cs3GdGe3O9 phosphors for WLEDs: non-concentration quenching and negative thermal expansion.

Ultra-high color rendering warm-white light-emitting diodes based on an efficient green-emitting garnet phosphor for solid-state lighting

A review and outlook of ratiometric optical thermometer based on thermally coupled levels and non-thermally coupled levels

Phosphor‐converted light‐emitting diode (pc‐LED) has drawn much interest due to the efficient light in solid‐state lighting, backlight display, security, and electronic devices. Thermal quenching (TQ) induced by nonradiative relaxation is one of the vital challenges that limits the widespread use of phosphors. Much efforts are devoted to designing different approaches to solve the emission loss at increasing temperature. Here, the mechanism of TQ and recent advances of anti‐TQ‐phosphor‐involved 5d–4f, 4f–4f, 6p–6s, 3d–3d transitions are discussed. Several important design strategies for anti‐TQ phosphors are summarized as follows: 1) defect engineering; 2) energy transfer; 3) structural modulation; 4) enhancing crystallinity; 5) layer structural design; 6) negative/zero thermal expansion; 7) surface coating and glass technology. Additionally, some future challenges and opportunities in this field are proposed. This review promotes the discovery of novel anti‐TQ phosphor materials for LED applications.

How to Obtain Anti‐Thermal‐Quenching Inorganic Luminescent Materials for Light‐Emitting Diode Applications

Afterglow materials are attracting widespread attention owing to their distinctive and long-lived optical emission properties which create exciting opportunities in various fields. Recent research has led to the discovery of many new afterglow materials featuring high photoluminescence quantum yields (PLQY) and lifetimes of up to several hours under ambient conditions. Afterglow materials are typically categorized according to their luminescence mechanism, such as long-persistent luminescence (LPL), room temperature phosphorescence (RTP), or thermally activated delayed fluorescence (TADF). Through rational design and novel synthetic strategies to modulate spin-orbit coupling (SOC) and populate triplet exciton states (T1), luminophores with long lifetimes and bright afterglow characteristics can be realized. Initial research towards afterglow materials focused mainly on pure inorganic materials, many of which possessed inherent disadvantages such as metal toxicity or low energy emissions. In recent years, organic-inorganic hybrid afterglow materials (OIHAMs) have been developed with high PLQY and long lifetimes. These hybrid materials exploit the tunable structure and easy processing of organic molecules, as well as enhanced SOC and intersystem crossing (ISC) processes involving heavy atom dopants, to achieve excellent afterglow performance. In this review, we begin by briefly discussing the structure and composition of inorganic and organic-inorganic hybrid afterglow materials, including strategies for regulating their lifetime, PLQY and luminescence wavelength. The specific advantages of organic-inorganic hybrid afterglow materials, including low manufacturing costs, diverse molecular/electronic structures, tunable structures and optical properties, and compatibility with a variety of substrates, are emphasized. Subsequently, we discuss in detail the fundamental mechanisms used by afterglow materials, their classification, design principles, and end applications (including sensing, anticounterfeiting, and photoelectric devices, among others). Finally, existing challenges and promising future directions are discussed, laying a platform for the design of afterglow materials for specific applications.

Recent advances in the design of afterglow materials: mechanisms, structural regulation strategies and applications.

Developing new luminescent host materials has always been played a great promotion role in efforts to obtain high-efficiency and practical phosphors. In this work, three new diphosphates, K5REE(P2O7)2 (REE = Y, Eu, Tb), with basic isotype crystal structures were synthesized by a flux method. The structure consisted of two-dimensional (2D) [REE(P2O7)2]∞ anionic layers stacked along the b-axis. Within the structure of K5Y(P2O7)2 (KYP), interlayer Y3+ ions were about 5.6 A away from each other, and intralayer Y3+ ions were separately larger than 9.5 A, which were long enough to avoid concentration quenching in a high density of Eu3+/Tb3+ activators. Consequently, the absolute luminescent internal quantum efficiency (IQE) of the K5Eu(P2O7)2 and K5Y0.2Tb0.8(P2O7)2 phosphors were measured as high values of 81% and 80%, respectively. Moreover, the KYP:Eu/Tb phosphors showed good thermal stability at 30–200 °C, keeping more than 86% of the initial intensity at 200 °C. The achievement of this work is to provide a new host lattice template KYP for both Eu3+ and Tb3+ luminescence with a high IQE and good thermal stability.

Non-concentration quenching, good thermal stability and high quantum efficiency of K5Y(P2O7)2:Eu3+/Tb3+ phosphors with a novel two-dimensional layer structure

Developing broad-band-emitting phosphors is very important to light-emitting diode (LED) lighting and displays. We introduced Eu2+ to solid solutions K2YZr1–yHfy(PO4)3 with a langbeinite-type struc...

Two-Site Occupancy Induced a Broad-Band Emission in Phosphor K2YZr(PO4)3:Eu2+ for White-Light-Emitting Diode Applications

The relationship between the structure and properties is always a hot topic in the luminescent material field. In this work, a new phosphor KBa2(PO3)5:Eu2+ (KBP:Eu) was prepared by a high-temperature solid-state reaction method and characterized by X-ray diffraction, energy-dispersive X-ray spectroscopy, photoluminescence (PL), and electroluminescence studies. The polyphosphate host KBP offers three lattice environments (K1, Ba1, and Ba2) for Eu2+ ions to realize broad-band emission from 380 to 700 nm under 345 nm excitation. The distributions of Eu2+ in the three lattice sites can be proven by low-temperature PL and transient fluorescence spectroscopy. Furthermore, temperature-dependent luminescence studies for phosphor KBP:0.02Eu reveal that its luminescence intensity at 150 °C retains about 97% of the initial value at 25 °C. By composing a 365 nm UV chip and KBP:0.02Eu, CaAlSiN3:Eu2+ phosphors, a warm white-light-emitting diode (WLED) was obtained with a correlated color temperature of 5146 K and chromaticity coordinates (0.3404, 0.3384). Therefore, KBP:Eu phosphor is a potential cyan-emitting phosphor used for high-power WLEDs.

Thermally Stable Phosphor KBa2(PO3)5:Eu2+ with Broad-Band Cyan Emission Caused by Multisite Occupancy of Eu2+

The rich compositional and structural diversity of borophosphates provides a wide variety of host lattices for luminescent materials. Herein, we report a borophosphate, CsNa2REE2(BO3)(PO4)2 (REE = Y, Gd), with a new type of three-dimensional (3D) anionic framework of [REE2(BO3)(PO4)2]∞. In this structure, REE3+ ions are in a linear array and the nearest intraline REE-REE distance is above 6.9 A. Surprisingly, the Eu3+ activated phosphors CsNa2REE2(1-x)Eu2x(BO3)(PO4)2 show an insignificant concentration quenching effect; the higher the Eu3+ concentration, the larger the absolute luminescent external quantum yield. The 100% Eu3+ phosphor CsNa2Eu2(BO3)(PO4)2 possesses an IQY of 59% under 394 nm excitation. Moreover, CsNa2Eu2(BO3)(PO4)2 phosphor possesses superior thermal stability in the range 30-200 °C, retaining more than 96% of its initial intensity at 200 °C. We believe the prepared phosphor has potential application as a red phosphor for NUV excited LEDs.

Design, synthesis, crystal structure and luminescent properties introduced by Eu3+ of a new type of rare-earth borophosphate CsNa2REE2(BO3)(PO4)2 (REE = Y, Gd)

The luminous efficiency of rare-earth (Ln3+)-doped luminescent materials suffers greatly from the negative concentration quenching effect, which can be surmounted by a large separation of Ln3+ ions in the host lattice. Herein, this study reports a novel tantalum-phosphate K3BiTaP3O13 (KBTP) that possesses a ‘chain-like’ structure when viewed along the c-axis, containing [TaO(PO4)2]∞, K∞ and [Bi(PO4)]∞ chains. UV-Vis spectroscopy and density functional theory (DFT) calculations reveal that K3BiTaP3O13 has an indirect band-gap of 3.99 eV, making it suitable as a luminescent host matrix. A series of Eu3+ or Tb3+ phosphors KBTP:xEu/Tb (x = 0.1–1) were prepared and their fluorescent performance was studied. Due to the Bi3+ ions being far apart in the KBTP host, the negative concentration quenching effect of the prepared phosphors was greatly limited, even when the concentration of Eu/Tb reached up to 80% replacing Bi3+. Moreover, both phosphors had good heat-resistance properties at 30–200 °C, keeping 85.6% (KBTP:0.8Eu) and 71.3% (KBTP:0.8Tb) of the initial intensity at 200 °C. These results preliminarily suggest that KBTP is promising as a host material for both Eu3+ and Tb3+ fluorescence.

Design, synthesis, crystal structure and luminescent properties of a new tantalum-phosphate K3BiTaP3O13 with negligible concentration quenching and good thermostability

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