Local Structure and Self‐Defect Evolution under Nonstoichiometric Effect Unlock Zero‐Thermal‐Quenching

Abstract

chip + yellow phosphors, (b) NUV LED chip + red-green-blue (RGB) phosphors. However, the former type features a low color rendering index (Ra) and residual rich blue light, which is not suitable to meet the increasingly prominent demand for human-centric health lighting. [2] NUVactivated w-LED shows a preponderance, for the acquisition of high-quality white light through the combination of different phosphors, meanwhile, the blue light can be minimized.In addition, during the working process, the Ohm effect caused by the current will unavoidably increase the temperature, then the emission intensity of phosphors will drop, and Stokes shift will drift, which is so-called thermal quenching. [3] This effect seriously drags down the overall luminescent efficiency and the total life of the devices, as well as the imbalance of white light. Therefore, the development of phosphors with high brightness and thermal stability is still a key challenge.Very recently, researchers have made positive efforts to explore low thermal quenching phosphors and delved novel strategies which can be summarized as follows: i) defect level regulation: as the defect levels make the supplement with emission center during high-temperature emission. [4] Kim et al. obtained a blue emitting zero-thermal quenching phosphor Na 3 Sc 2 (PO4) 3 :Eu 2+ via its polymorphism transition (α−β−γ) and their defects correspondingly. [5] Wu et al. explored an antithermal quenching red emitting NaZn(PO 3 ) 3 :Mn 2+ and discovered the trap compensation effect during the self-reduction process. [6] However, one must concern about the lack of certain common principles and the uncertainty of traps in different hosts. ii) Structural modulation, which begins from the structure itself, searching or enhancing the rigidness of crystal structure to reduce thermally activated phonons-assisted non-radiative process under high temperature. [7] For instance, this is discovered in some UCr 4 C 4 type structures (e.g., RbLi(Li 3 SiO 4 ) 2 :Eu 2+ , NaK 2 Li(Li 3 SiO 4 ) 4 :Eu 2+ , NaK 7 (Li 3 SiO 4 ) 8 :Eu 2+ et al.), however, this is limited in its poor chemical stability. [8] iii) Surface and interface engineering, which is constructed by making phosphors into a core-shell structure or making phosphors-in-glass for higher chemical and thermal stability. Although effective, such as Ca 3 SiO 4 Cl 2 :Eu 2+ @SiO 2 , RbLi(Li 3 SiO 4 ) 2 :Eu 2+ @ Al 2 O 3 @ODTMS, the complexity, and extensibility of the process still limit practical production. [9] Therefore, newly efficient

Composition–structure–luminescence and enhancement of Cr3+ activated broadband near infrared phosphors for night vision, bio-imaging, and noninvasive detection

“…Based on the refinement result about the bond length of KSc 0.97 Cr 0.03 P 2 O 7 listed in Table S3 (ESI†), the distortion index of the [Sc/CrO 6 ] octahedron can be estimated to be 0.008, suggesting a highly symmetrical local coordinated environment. 35–37…”

A Robust Anti-Thermal-Quenching Phosphor Based on Zero-Dimensional Metal Halide Rb3InCl6:xSb3+

“…This can be explained by assuming that at higher Δ the samples have a higher density of structural vacancies, resulting in a slight contraction of the lattice. 19 The formation of vacancies was further proven by 85 Rb magic angle spinning (MAS) nuclear magnetic resonance (NMR) characterization (Figure S18), which evidenced at least four different 85 Rb peaks in the range from 100 to −100 ppm. Considering that Rb + ions occupy two different locations (Rb 1 , Rb 2 ) in the tetragonal Rb 3 InCl 6 phase, 22 the NMR spectra indicated that the two types of Rb atoms could be surrounded by either 6 [InCl 6 ] 3− or 5 [InCl 6 ] 3− octahedra and 1 In vacancy, 32,33 which further splits the number of Rb sites to four, (Rb 1 , Rb 1-v ) and (Rb 2 , Rb 2-v ), resulting in 2*2 multiplets.…”

“…Via efficient energy transfer from defects to Eu 2+ emitting centers, in the optimal sample (Δ = 0.1%), the PL intensity at 498 K corresponded to 114% of its initial value at room temperature. 19 The problem with metal oxides/nitrides is that their syntheses require high temperatures (>1500 K). 7 Metal halides, on the other hand, can profit from the much lower synthesis temperatures (some of them can even be prepared at room temperature) and, for some members of the class, the high photoluminescence quantum yield (PLQY).…”

“…27−29 In the synthesis, the In 3+ precursor was added in a substoichiometric amount, that is (1 − Δ) × n moles (where n moles would correspond to the stoichiometric amount required to synthesize Rb 3 InCl 6 ) with the aim to induce the formation of structural defects. 19 By tuning the stoichiometric deficiency Δ (henceforth reported in % terms, that is, Δ/100) of the added In precursors and alloying at the Rb + site with other cations (K + , Cs + ), we could prepare optimal Rb 3−y Cs y InCl 6 :xSb 3+ samples that did not show luminescence quenching at temperatures up to 500 K, making them comparable to the best metal oxide/nitride-based anti-TQ phosphors to date. 2,7,9 The sample's structure and luminescence were preserved after several cycles of heating−cooling.…”

Novel highly efficient Bi3+-activated phosphors for warm WLEDs

“…[1][2][3][4][5][6][7][8][9] Compared with traditional light sources, phosphor-converted WLED (pc-WLED) technology has become the dominant light source because of its advantages of high efficiency, environmental protection, fast response time, and small volume. [10][11][12][13][14][15][16][17] Considering the application needs of various fields, there is still great room for the progress of pc-WLED technology. The color rendering index (CRI) is an important parameter to evaluate the quality of pc-WLEDs, and the higher the CRI, the better the color reproduction.…”