Progress in discovery and structural design of color conversion phosphors for LEDs

Nowadays, phosphor converted white light-emitting diodes (pc-WLEDs) have been widely used in solid-state lighting and display areas due to their superior lifetime, efficiency, and reliability as well as significant reduction in power consumption. Phosphors are indispensable components of pc-WLED devices, and their luminescence properties determine the quality of WLED lighting and displays. In order to further achieve high luminous efficacy, chromatic stability, and color-rending properties in pc-WLEDs, much effort has been focused on improving current pc-WLED phosphors and developing novel pc-WLED phosphors recently. This review article concerns commonly used rare earth ion (Eu2+ and Ce3+) activated inorganic phosphors, highlighting the important effect of spectral tuning via local structural variations on improving the luminescence performance of phosphors. The main spectral tuning strategies are discussed in detail and summarized, including (1) doping level control; (2) cationic substitution; (3) anionic substitution; (4) cationic–anionic substitution; (5) the crystal-site engineering approach; (6) mixing of nanophases.

Recent progress in luminescence tuning of Ce3+ and Eu2+-activated phosphors for pc-WLEDs

Phosphor-converted white light-emitting diodes (pc-WLEDs) are efficient light sources used in lighting, high-tech displays, and electronic devices. One of the most significant challenges of pc-WLEDs is the thermal quenching, in which the phosphor suffers from emission loss with increasing temperature during high-power LED operation. Here, we report a blue-emitting Na3–2xSc2(PO4)3:xEu2+ phosphor (λem = 453 nm) that does not exhibit thermal quenching even up to 200 °C. This phenomenon of zero thermal quenching originates from the ability of the phosphor to compensate the emission losses and therefore sustain the luminescence with increasing temperature. The findings are explained by polymorphic modification and possible energy transfer from electron–hole pairs at the thermally activated defect levels to the Eu2+ 5d-band with increasing temperature. Our results could initiate the exploration of phosphors with zero thermal quenching for high-power LED applications. A blue-emitting phosphor without thermal quenching is reported. The emission losses at high temperatures are compensated by a counter mechanism, originating in energy transfer between electron–hole pairs and thermally activated defect levels.

A zero-thermal-quenching phosphor

Advances in solid state white lighting technologies witness the explosive development of phosphor materials (down-conversion luminescent materials). A large amount of evidence has demonstrated the revolutionary role of the emerging nitride phosphors in producing superior white light-emitting diodes for lighting and display applications. The structural and compositional versatility together with the unique local coordination environments enable nitride materials to have compelling luminescent properties such as abundant emission colors, controllable photoluminescence spectra, high conversion efficiency, and small thermal quenching/degradation. Here, we summarize the state-of-art progress on this novel family of luminescent materials and discuss the topics of materials discovery, crystal chemistry, structure-related luminescence, temperature-dependent luminescence, and spectral tailoring. We also overview different types of nitride phosphors and their applications in solid state lighting, including general ...

Down-Conversion Nitride Materials for Solid State Lighting: Recent Advances and Perspectives.

Stable and efficient phosphor systems for white light-emitting diodes (LEDs) are highly important with respect to their application in solid-state lighting beyond the technical limitations of traditional lighting technologies. Therefore, inorganic solid-state conversion phosphors must be precisely selected and evaluated with regard to their special material properties and synergistic optical parameters. In this perspective, we present an overview of the recent developments of LED phosphors; firstly, general photoluminescence-controlling strategies for phosphors to match LED applications have been evaluated; secondly, state-of-the-art and emerging new LED phosphors have been demonstrated. Then, methodologies for the discovery of new LED phosphors by mineral-inspired prototype evolution and new phase construction, as well as combinatorial optimization screening, and the single-particle-diagnosis approach, have been analyzed and exemplified. Finally, future developments of LED phosphors have been proposed.

Recent developments in the new inorganic solid-state LED phosphors

Manganese-activated fluoride phosphors for high-efficacy warm white light-emitting diodes have been limited by low photoluminescence quantum yields. Here, Zhu et al. use an efficient cation exchange reaction to synthesize manganese phosphors with photoluminescence quantum yields as high as 98%.

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Highly efficient non-rare-earth red emitting phosphor for warm white light-emitting diodes

Single-composition (or single-phase) phosphors have been proposed as a new strategy to overcome the concerns of emission reabsorption and different degradation rates of the three primary phosphors for light-emitting diode (LED) applications. A series of Ce3+, Sm3+ and Tb3+ co-doped NaSrBO3 phosphors were synthesized via a high temperature solid-state reaction. Upon near ultraviolet (NUV) excitation, tunable emission from violet to white in the visible region was realized in NaSrBO3:Ce3+,Sm3+,Tb3+ phosphors by controlling the dopant concentrations. Particularly, highly efficient white-light emission with a quantum yield as high as 48.2% was achieved. The energy transfer mechanism between Ce3+ and Sm3+ ions in NaSrBO3 was found to be predominantly of dipole–dipole nature. Moreover, the thermal quenching effect on the photoluminescence of NaSrBO3:Ce3+,Sm3+,Tb3+ was comprehensively surveyed over the range of 300–600 K, showing a good thermal stability for LED applications. By integrating this single-composition white-emitting NaSrBO3:Ce3+,Sm3+,Tb3+ phosphor with a 360 nm NUV chip, we fabricated a high-performance white LED (WLED), which exhibited an excellent color rendering index Ra of 80.1 and a correlated color temperature of 6731 K with CIE coordinates of (0.311, 0.314). These findings demonstrate that the proposed single-composition white-emitting NaSrBO3:Ce3+,Sm3+,Tb3+ phosphors can serve as promising phosphors for NUV-excited WLEDs.

Single-composition white-emitting NaSrBO3:Ce3+,Sm3+,Tb3+ phosphors for NUV light-emitting diodes

Abstract Sesquioxides such as Y 2 O 3 and Sc 2 O 3 are important optical materials, but the fabrication of their transparent ceramics remains a challenge due to the ultra-high melting point of over 2400 ° C. In this work, a series of (Y 1− x Sc x ) 2 O 3 transparent ceramics were successfully fabricated by a simple vacuum sintering process without any sintering additives, and the effect of scandium (Sc) content ( x ) on the crystal structure and optical/thermal/mechanical properties was evaluated. Y 2 O 3 and Sc 2 O 3 form a complete solid solution with a cubic bixbyite structure. The formation of (Y 1− x Sc x ) 2 O 3 solid solution promotes the densification of ceramics, leading to the realization of high transparency close to the theoretical transmittance over a wide wavelength range of 0.35–8 µm. In particular, the in-line transmittance in the range of 0.6–6 µm remains above 80% for (Y 1− x Sc x ) 2 O 3 with x = 0.23–0.31, while the pristine Y 2 O 3 and Sc 2 O 3 are opaque. Moreover, the mechanical properties including Vickers hardness ( HV ), fracture toughness ( K IC ), and biaxial flexural strength ( δ b ) are evidently enhanced due to the solid solution strengthening, while the thermal conductivity ( k ) is reduced due to the reduction of photon free path. This study demonstrates that forming of solid solution is a facile and universal approach for preparing sesquioxide transparent ceramics with high optical and mechanical quality. 

Optical, thermal, and mechanical properties of (Y1−xScx)2O3 transparent ceramics

With the rapid development of the renewable energy industry, the traditional renewable energy asset transaction mode is facing great challenges in terms of the transaction cycle, security, work efficiency, and so on. This report analyzes the current situation of renewable energy asset transactions and system platforms. The purpose of this paper is to show the study of renewable energy asset transaction standard framework and standard content. Furthermore, this paper presents the concept of market-oriented renewable energy asset transaction, explains the basic framework of renewable energy asset transaction standards, and proposes a series of renewable energy asset transaction standards. Finally, it analyses the elements that need to be paid attention to promote the standardization of renewable energy asset transactions. The work pushes forward the coordinated development of science and technology, industry and finance of the renewable energy industry chain, and provides standardized support for convenient circulation and high-quality development in the renewable energy field. 

https://madison-proceedings.com/index.php/aemr/article/download/602/613

Zhuguang Liu

Papers

Highly efficient non-rare-earth red emitting phosphor for warm white light-emitting diodes

Single-composition white-emitting NaSrBO3:Ce3+,Sm3+,Tb3+ phosphors for NUV light-emitting diodes

Optical, thermal, and mechanical properties of (Y1−xScx)2O3 transparent ceramics

Study on Standardization of Renewable Energy Asset Transaction

Photoluminescence and persistent luminescence properties of Lu3ScAl4-Ga O12: Ce3+ ceramics