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 illumination, backlighting, and laser-driven lighting. Finally, the challenges and outlooks in this type of promising down-conversion materials are highlighted.

The near-infrared phosphor-converted light-emitting diodes (NIR pc-LEDs) have great potential in food industry and medical fields. For applications based on NIR spectroscopy, the next generation of NIR pc-LEDs is in a high demand of a spectrum with a much broader full width at halfmaximum (fwhm), which triggers the discovery of novel broadband NIR phosphors. In this work, the Cr 3+ -doped La 2 MgZrO 6 (LMZ) was successfully synthesized by a conventional solid-state method in a reducing atmosphere, and the double-perovskite oxide LMZ with two distorted octahedral sites finally led to an ultra-broadband Cr 3+ emission centered at 825 nm with an extremely large fwhm of 210 nm and an internal quantum efficiency of ∼58%. The experimental data and theoretical calculation confirmed that two available Cr 3+ sites with different crystal field environments contributed to the broadband emission. The crystal field parameters, decay time, and temperature-dependent photoluminescence properties were investigated and discussed to further understand the luminescence of Cr 3+ in LMZ:Cr. The suitability of the title NIR phosphor in multifunctional pc-LEDs was demonstrated by pumping it with blue, green, and/or red LED chips.

Low-dimensional organic−inorganic metal halide hybrids (OIMHs) with an ultrabroad-band emission are promising as downconversion phosphors for solid-state lighting. However, toxicity of Pb and low photoluminescence quantum efficiency (PLQE) hamper their application. Herein, two zero-dimensional (0D) lead-free organic antimony (Sb) chloride (Cl) hybrids with dual-band emissions and PLQEs: (TTA) 2 SbCl 5 (TTA = tetraethylammonium) and (TEBA) 2 SbCl 5 (TEBA = benzyltriethylammonium) are reported. Both compounds show a single broad-band orange emission with a near-unity PLQE upon low-energy photons (e.g., 360 nm) excitation. The dual-band emission with an additional blue emission band upon high-energy photons (e.g., 300 nm) excitation enable (TTA) 2 SbCl 5 to be a single-component phosphor for white light emission with a PLQE of 68%, correlated color temperature (CCT) of 2360 K and color rendering index (CRI) of 84. Based on photoluminescence spectra measurements and density functional theory calculations, the dual-band emission is assigned to the radiative recombination from both singlet and triplet self-trapped excitons in inorganic [SbCl 5 ] 2− pyramids. In addition, both luminescent compounds exhibit excellent stability against humidity and thermal attacks. Using (TEBA) 2 SbCl 5 as a yellow downconversion material, highly stable white-light-emitting diodes with a Commission Internationale de l'Eclairage (CIE) of (0.36, 0.33), CCT of 4282 K, and CRI of 82 were demonstrated. These results validate that the title 0D lead-free OIMHs with a dual-band emission and a near-unity PLQE are promising luminescent materials for solid-state lighting.

Divalent europium-activated ␤-sialon ͑Si 6−z Al z O z N 8−z , 0.1 ഛ z ഛ 2.0͒ phosphors with dopant concentration varying in the range of 0.02-1.5 mol % were synthesized by firing the powder mixture of ␣at 2000°C for 2 h under a nitrogen-gas pressure of 1.0 MPa. The phase purity, microstructure, luminescence spectra, and thermal quenching of the fired ␤-sialon:Eu 2+ phosphors were investigated. The samples with lower z values ͑z ഛ 1.0͒ showed higher phase purity, finer and more uniform particle size, and higher emission. Green luminescence of Eu 2+ ͑ em = 528-550 nm͒ was achieved in ␤-sialons upon near-ultraviolet ͑NUV͒ or blue-light excitations. Furthermore, the ␤-sialon:Eu 2+ phosphors had small thermal quenching, the emission intensity of which attained 84-87% of that measured at room temperature. The experimental data clearly indicates that ␤-sialon:Eu 2+ has great potentials as a down-conversion green phosphor for white light-emitting diodes ͑LEDs͒ utilizing NUV or blue LEDs as the primary light source.

Mechanoluminescence (ML) is the emission of light when a solid material is subjected to stress. [8][9] The intensity of the ML shows a strong correlation with the applied stress, making it suitable for stress sensing. ML stress sensing is based on a unique transduction principle from stress to photons, which paves the way for advanced stress sensing. In particular, ML-based sensing shows significant advantages of distributed detection and remote response to an applied stress by virtue of photon transmission through space. In addition, excellent stretchability, biocompatibility, and self-powering ability can be achieved within the stress-tophoton transduction units since electronic conduction is not needed. Importantly, ML-based sensing enables compensation of the shortcomings of conventional sensing technologies for emerging applications. Considering the many extraordinary performance characteristics, ML may hopefully rebrighten the prospects of stress sensing.Over the past few decades, ML materials and ML-based stress sensing have been extensively studied. Great efforts have been made to develop a large number of ML materials, deeply understand the ML mechanism, and boost the potential for stress sensing applications. Several review papers have been devoted to ML and its applications. [10][11][12][13][14][15][16][17] Bunzil and Wong summarized ML materials and stress sensors based on lanthanide compounds. [10] Xie and Li surveyed the progress in ML compounds with a focus on fractoluminescence. [11] An overview of inorganic ML compounds was presented by Feng and Smet, which particularly provides deep insight into the crystal structures and their relation to ML. [12] Additionally, Zhang et al. reviewed inorganic ML compounds, concentrating on their compositions, preparation, characterizations, mechanisms, and applications. [13] However, compared with materials and mechanisms, less attention has been paid to the technical performance of ML-based stress sensing and its relevance to applications. Obviously, reasonable analyses of the up-to-date performance are beneficial for properly assessing the potential for future applications.In this paper, we start with a brief overview of the desired performance characteristics of advanced stress sensing for several new applications (Section 2). The state-of-arts and challenges are highlighted. In Section 3, ML materials, ML-based sensors, and technical features will be discussed in an attempt to comprehensively evaluate ML-based sensing technology andThe emergence of new applications, such as in artificial intelligence, the internet of things, and biotechnology, has driven the evolution of stress sensing technology. For these emerging applications, stretchability, remoteness, stress distribution, a multimodal nature, and biocompatibility are important performance characteristics of stress sensors. Mechanoluminescence (ML)-based stress sensing has attracted widespread attention because of its characteristics of remoteness and having a distributed response to mechanical stimuli...