Tuning Eu²⁺ luminescence in Sr₈CaLu (PO₄)₇via Na⁺-induced local structure engineering for violet-chip-excitable full-spectrum lighting

Abstract

Currently, white light-emitting diodes (wLEDs), designed by combining violet chips (400–420 nm) and multi-color phosphors, are highly desirable for reducing blue light hazard and improving visual comfort. However, green–yellow phosphors with excellent optical performance are scarce so far. Herein, we develop a new type of violet-light-excitable green–yellow Eu²⁺:Sr₈CaLu(PO₄)₇ phosphor with Na⁺ alloying. Benefiting from Na⁺-induced local structural modification, Eu²⁺ luminescence shows gradual red-shifting from 520 nm to 550 nm, with photoluminescence quantum yields (PLQYs) remaining above 70%, decay lifetimes increasing from 1200 ns to 1800 ns, and PL bandwidths enlarging from 110 nm to 172 nm. First-principles density functional theory (DFT) calculations, together with temperature-dependent PL spectra and time-resolved PL spectra analysis, verify the modulation of the proportions of SrO₉, SrO₈ and SrO₆ polyhedra for Eu²⁺ multiple cationic occupation via Na⁺ doping is responsible for the observed PL phenomenon. Finally, we design full-spectrum wLEDs with ultra-high color rendering indexes (CRI, R_a and R10) above 95 by coupling the as-prepared Eu²⁺/Na⁺:Sr₈CaLu(PO₄)₇ phosphor and commercial blue/red phosphors with a violet LED chip, which shows promising applications in healthy solid-state lighting.

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Introduction

With the continuous progress of science and technology, the realization of sunlight-like healthy lighting has become more and more important.^1–6 Currently, commercial wLEDs are designed by coupling an InGaN blue chip with a Ce³⁺:Y₃Al₅O₁₂ yellow phosphor and red phosphors such as Eu²⁺:CaAlSiN₃ and Mn⁴⁺:K₂TiF₆.^7–10 Unfortunately, this strategy suffers from “blue light hazard”, i.e., exposure to excess blue light which leads to the disruption of circadian rhythms and eye diseases such as cataracts and macular degeneration.^11,12 On the other hand, due to the absence of violet light, the “sunlight-like full spectrum” cannot be realized.¹³ The other scheme is to adopt near-ultraviolet (n-UV) light to excite multi-color phosphors.^14–22 However, the usage of a high-energy 365 nm n-UV chip as an excitation source will cause a large amount of energy loss.²³ Moreover, human eyes have a low perception of n-UV light and excess n-UV light irradiation will harm the human body.²⁴

As an alternative, it has recently been proposed to use violet light (400–420 nm) to excite various phosphors, which has the advantage of low energy loss and easy simulation of the sunlight-like spectrum. Notably, violet chips have an external efficiency of 80%, higher than that of 365 nm n-UV chips (44%).²⁵ Therefore, violet-chip excitable wLEDs have significant application prospects. This puts forward higher demand for phosphors that can be effectively pumped by violet light. However, few types of phosphors excitable by violet light have been reported so far,^26–37 especially green–yellow ones.^38,39 Herein, we report the local structural engineering of a Eu²⁺-doped Sr₈CaLu(PO₄)₇ (Eu:SCLP) phosphor via Na⁺ doping (Eu:Na-SCLP) to produce efficient and tunable green–yellow emissions of Eu²⁺ from 520 nm to 550 nm for the first time. The phosphors can be efficiently excited by violet light and show high PLQYs of ∼75%. First-principles DFT calculations evidenced that such significant spectral shifting is mainly ascribed to Na⁺-doping induced change of the fractions of distinct cation sites. Finally, we construct a sunlight-like wLED by coupling it with a violet chip and commercial blue/red phosphors, producing an ultra-high R10 index of 97 owing to compensation for the yellow gap between the green and red spectral ranges.

Experimental section

Synthesis

Eu:Na-SCLP phosphors were prepared via a high-temperature solid-phase reaction. The nominal feeding concentration of Na₂CO₃ was 0–1.5 g per 0.003 mol Eu:SCLP. High-purity raw materials, including SrCO₃ (99.9%), CaCO₃ (99.9%), NH₄H₂PO₄ (99.9%), Lu₂O₃ (99.9%), Eu₂O₃ (99.9%), and Na₂CO₃ (99.9%), were mixed thoroughly and heated in a tube furnace at 1580 °C for 5 h under a reducing atmosphere of N₂–H₂ (5%). After firing, the products were naturally cooled to room temperature in the furnace and were ground again for further usage.

Fabrication of wLED

The device was constructed by coupling a violet (410 nm) chip with a commercial Eu²⁺:BaMgAl₁₀O₁₇ (Eu:BAM) blue phosphor, Eu²⁺:CaAlSiN₃ (Eu:CASN) red phosphor and the as-synthesized Eu:Na-SCLP green–yellow phosphor with an appropriate mass ratio. In the packing process, the organic silicone A glue and B glue with a mass ratio of 1 : 4 were thoroughly mixed with the phosphors. Then, the mixture was dripped onto the violet chip and the packaged wLED was dried in a box oven at 150 °C for 1 h.

Characterization

X-ray diffraction (XRD) analysis was carried out to identify the crystalline phase structures of Eu:Na-SCLP phosphors using a Bruker D8 Advance X-ray powder diffractometer with Cu K_α radiation (λ = 0.154 nm) operating at 40 kV. The crystal structures of the products were refined using General Structure Analysis System (GSAS) software. The actual chemical compositions were measured by inductively coupled plasma–mass spectrometry (ICP-MS) using a PerkinElmer Optima 3300DV spectrometer. X-ray photoelectron spectroscopy (XPS, Thermo Scientific K-Alpha) data were recorded to examine the chemical elements and valence states of samples using a spectrometer equipped with two ultra-high vacuum chambers. Notably, the C 1s peak of the surface adventitious carbon at 284.80 eV was used as the reference for all the samples. The microstructures of the samples were characterized using a scanning electron microscope (SEM, SU8010) equipped with an energy dispersive X-ray (EDX) spectroscopy system. Diffuse reflectance spectra were recorded on a spectrophotometer (Lambda900, PerkinElmer) with a resolution of 1 nm. Photoluminescence (PL) spectra, PL excitation (PLE) spectra, and decay curves were recorded on an Edinburgh Instruments FLS1000 spectrofluorometer equipped with a continuous xenon lamp (450 W), a pulsed flash lamp, and a 375 nm picosecond pulsed laser. The corresponding decay lifetimes were evaluated using the equation: , where I₀ is the peak intensity and I(t) is the time-related emissive intensity. The PL quantum yield (PLQY) is equal to the ratio of the emitted photons to the absorbed photons and was measured in FLS1000. Electroluminescence (EL) spectra, luminous efficacy (LE) and correlated color temperature (CCT), as well as the CRI of the fabricated wLEDs, were recorded on a spectrometer (PMA-12) equipped with a fiber optic integrating sphere under dark conditions.

Theoretical calculations

First-principles calculations of structural properties for SCLP and Na-SCLP with different Na⁺ doping concentrations were performed within the DFT formalism, as implemented in the Vienna Ab initio Simulation Package (VASP). The frozen-core projected augmented wave (PAW) method with the generalized gradient approximation (GGA) formulated by Perdew–Burke–Ernzerhof (PBE) as the exchange–correlation functionals was adopted to describe the electron–core interactions. The Brillouin zone (BZ) for integrations in the reciprocal space was sampled with a grid of 3 × 3 × 1 conducted by the Monkhorst–Pack special k-point scheme. Moreover, in all computations, the electronic wavefunctions were expanded on a plane-wave basis with an energy cutoff of 520 eV, and the cell parameters and atomic positions were fully relaxed until the energy and residual forces on atoms converged to 1 × 10⁻⁶ eV and declined to 0.01 eV Å⁻¹ by applying the conjugate-gradient algorithm, respectively.

Results and discussion

SEM image of a typical Eu

The Na-SCLP sample shows micron-sized (∼30 μm) crystals with irregular shapes (Fig. 1a). EDX mapping on an individual particle shows that all the elements, including Sr, Ca, Lu, P, Na and Eu, are homogeneously distributed throughout the particle and no aggregation is observed (Fig. 1b). This result verifies the successful incorporation of Na⁺ dopants into the SCLP lattice. To confirm this conclusion, the actual Na⁺ concentration was determined using ICP-MS data. Indeed, as evidenced in Fig. 1c, the Na⁺ concentration gradually increases up to 10 mol% as the nominal Na⁺ feeding content increases. XPS full survey data were recorded to further determine the chemical distribution and valences (Fig. 1d), showing the existence of Sr, Ca, Lu, Na, Eu, P and O elements. As shown in Fig. 1e, two typical peaks at 1135 eV and 1165 eV are attributed to Eu²⁺:3d_5/2 and 3d_3/2, respectively, confirming the successful reduction of Eu³⁺ into Eu²⁺ for the present samples.

Fig. 1 (a) SEM image of the Eu:Na-SCLP phosphors and (b) the corresponding EDX mapping from a typical particle. (c) The actual concentration of Na⁺ dopants into SCLP host versus the nominal Na₂CO₃ feeding content. (d) XPS full survey and (e) high-resolution XPS profiles of Eu 3d for the Eu:SCLP and Eu:Na-SCLP samples.

XRD patterns for all the samples were recorded to characterize the phase purity and coordination environment of the as-prepared products (Fig. S1a†). Rietveld refinements of Eu:SCLP and three typical Eu:Na-SCLP samples with different Na⁺ doping concentrations (2.0, 3.3, and 9.6 mol%) were performed based on their XRD patterns using the GSAS method, as revealed in Fig. S1b–S1e.† Herein, a whitlockite-type Sr₉In(PO₄)₇ (ICSD card no. 59722) crystal structure was chosen as the typical model for the refinement.⁴⁰ Notably, the calculated results agree well with the raw data, and all the diffraction peaks completely match the Bragg reflection positions, suggesting that no impurity phase exists in these phosphors after Na⁺ doping. The obtained crystal parameters based on the refinement results are tabulated in Table 1. The suitable values of R_wp, R_p and χ² indicate the credible refinement results. All the Eu:SCLP and Eu:Na-SCLP products show a monoclinic structure with a space group of I2/a. The Na⁺ doping will not destroy the SCLP host structure and increasing Na⁺ doping concentration will lead to a slight expansion of the crystal structure.

Table 1 Rietveld refinement results for the Eu:Na-SCLP phosphors with various Na⁺ doping concentrations

Na^+ content (mol%)	0	2.0	3.3	9.6
Space group	I2/a	I2/a	I2/a	I2/a
a (Å)	18.0084	18.0066	18.0414	18.0478
b (Å)	10.6582	10.6690	10.7126	10.7014
c (Å)	18.4598	18.4645	18.5078	18.5278
α (°)	90	90	90	90
β (°)	133.0691	133.0611	133.1167	133.1720
γ (°)	90	90	90	90
V (Å^3)	2588.365	2591.715	2611.088	2609.746
Z	4	4	4	4
R wp (%)	6.04	4.94	6.01	6.42
R p (%)	4.06	3.62	4.32	4.63
χ ^2	2.265	1.218	1.219	1.674

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PL spectra for the Eu

SCLP samples with various Eu²⁺ doping concentrations were recorded, as shown in Fig. S2.† The optimal Eu²⁺ concentration is 7 mol%, which is adopted for the following Na⁺-doped samples. Diffuse reflectance spectra of Eu:SCLP phosphors with different Eu²⁺ concentrations are presented in Fig. S3.† Importantly, the addition of Eu²⁺ induces extra strong absorption (300–450 nm) covering the violet light range, which is assigned to the Eu²⁺:4f → 5d transition and is gradually enhanced with an increase of Eu²⁺ concentration. PLE spectra and PL spectra for the Eu:Na-SCLP samples with various Na⁺ concentrations are provided in Fig. 2a. A broadband green emission originating from Eu²⁺:5d → 4f transition is detected for the Eu:SCLP sample, and the corresponding PLE spectrum shows a strong absorption near 400 nm, which covers a spectral range of 250–450 nm and matches well with a violet LED chip. Impressively, with increasing Na⁺ concentration, a remarkable red-shift of the Eu²⁺ PL band from 520 to 554 nm is observed (Fig. S4,†Fig. 2a and the inset of Fig. 2b), leading to variation of the emitted color of the phosphor from green to yellow (Fig. 2b). In addition, it is found that the red-shifting of the emitted wavelength will result in broadening emission with an increase in the full width at half maximum (FWHM) from 110 nm to 172 nm (Fig. 2c) and an elongating decay lifetime from 1200 ns to 1800 ns (Fig. 2d). Herein, the FWHM value is determined by dividing the PL-integrated intensity by the PL peak intensity. Importantly, the PLQY and external quantum yield (EQY) values remain almost unchanged above 70% and 50% for the samples in the emitting wavelength range from 525 nm to 547 nm (Fig. 2e and Table S1†). Notably, high Na⁺ doping content may result in the formation of defect states acting as quenching centers, which will lead to a slight decrease in PLQY and EQY.

Fig. 2 (a) PLE/PL spectra and luminescence photographs of Eu:SCLP and Eu:Na-SCLP phosphors with various Na⁺ concentrations. (b) CIE color coordinations of the emitting colors from the corresponding samples. Inset shows the dependence of emitting peak wavlength on the Na⁺ concentration. (c) FWHM, (d) the decay lifetime and (e) PLQY & EQY versus the emitting wavelength of Eu:Na-SCLP phosphors.

Fig. 3a and b show two typical asymmetric PL spectra from Eu:SCLP and Eu:Na-SCLP phosphors, which can be actually divided into three sub-bands according to the Gaussian multi-peak fitting. These three PL bands are located at 509 nm (band 1), 554 nm (band 2) and 624 nm (band 3), respectively, which are attributed to Eu²⁺ 5d → 4f transition at three distinct coordination environments. Interestingly, PL band 1 decreases, PL band 2 remains almost unchanged, while PL band 3 significantly enhances after Na⁺ doping (Fig. 3a and b). To confirm this conclusion, the integrated PL intensities for these three bands versus Na⁺ doping concentration are plotted in Fig. 3c. Indeed, with increasing Na⁺ concentration, the PL intensity of band 1 gradually weakens, but the PL intensity of band 3 shows the opposite result, and the PL intensity of band 2 remains unaltered. When the Na⁺ doping concentration reaches a critical value, the intensities of these three bands become stable. Therefore, it can be concluded that the PL red-shifting of Eu:SCLP upon Na⁺ doping is due to the change in the Eu³⁺ amounts in these three different coordination environments. We further detected PL decay curves by monitoring different emission wavelengths for the Eu:SCLP and Eu:Na-SCLP samples, and the corresponding decay lifetimes are presented in Fig. 3d. Obviously, the PL decay lifetime of the Eu:SCLP gradually elongates with an increase in emission wavelength. This result confirms that the broadband luminescence originates from Eu²⁺ 5d → 4f transition in different coordination environments and a longer lifetime is obtained for the longer-wavelength (lower-energy) emission. A similar lifetime trend is found for the Eu:Na-SCLP sample, but the lifetime of Eu:Na-SCLP at each wavelength is longer than that of Eu:SCLP, which is ascribed to the increased ratio of lower-energy emission relative to the higher-energy one after Na⁺ doping.

Fig. 3 Gaussian multi-peak fitting PL spectra of (a) Eu:SCLP and (b) Eu:Na-SCLP samples. (c) Dependence of PL intensities for the fitted three bands on the Na⁺ doping concentration. (d) Emission wavelength dependent decay lifetime for the Eu:SCLP and Eu:Na-SCLP phosphors. (e) Pseudo-color contour mapping of TRPL spectra for a typical Eu:Na-SCLP sample and (f) normalized TRPL curves with various delay times.

To verify Eu²⁺ luminescence from different crystallographic sites, time-resolved PL (TRPL) spectra were recorded (Fig. S5†). The PL intensity for each monitored emission wavelength gradually weakens when the delay time is set to increase from 0 to 20 μs, as evidenced in Fig. 3e. Due to the short lifetimes of the Eu²⁺ shorter-wavelength emission, its PL decay is faster than that of the Eu²⁺ longer-wavelength emission (Fig. 3f). Therefore, with elongation of the delay time, the short-wavelength emission disappears while the long-wavelength emission still remains. All these results certainly confirm that Eu²⁺ activators stay in the multiple cations sites in the Na-SCLP host.

Furthermore, temperature-dependent PL behaviors for the Eu:SCLP and Eu:Na-SCLP samples are studied. With elevation of temperature, the PL intensity continuously weakens for both phosphors owing to the thermal quenching effect (Fig. 4a and b). Notably, the temperature-induced decreasing PL rate of Eu:Na-SCLP is slightly higher than that of Eu:SCLP (Fig. 4c). Interestingly, the FWHMs for both samples show a tendency of narrowing with elevation of temperature (Fig. 4d). This phenomenon is quite opposite to the case for traditional phosphors previously reported,⁴¹ where the PL band becomes broaden with an increase of temperature owing to the role of enhanced electron–phonon coupling. All these results should be attributed to the multiple cation sites for Eu²⁺ substitution in the SCLP host and the more serious thermal quenching of long-wavelength emission of Eu²⁺ activators than for short-wavelength emission, which will be clarified in the following section.

Fig. 4 (a) Temperature-dependent (80–470 K) PL spectra for Eu:SCLP and (b) Eu:Na (3.3 mol%)-SCLP samples. The evolution of (c) PL integrated intensity and (d) FWHM as a function of temperature for both samples.

To elucidate the Na⁺-induced tunability of Eu²⁺ luminescence in the SCLP host, first-principles calculations based on DFT were performed to get the information on structural modification of the SCLP via Na⁺ doping. The optimized crystal structure configurations of SCLP and Na-SCLP with different Na⁺ concentrations are depicted in Fig. 5a–d. Consistent with previous study,⁴² Lu³⁺ and P⁵⁺ cations in SCLP are surrounded by six and four oxygen atoms to form LuO₆ and PO₆ tetrahedra, respectively, while Sr ions are located in different coordination environments to form SrO₉, SrO₈ and SrO₆ polyhedra (Fig. 5a). The ratios for the SrO₉, SrO₈ and SrO₆ in SCLP are 20.8%, 72.9% and 6.3%, respectively (Table 2). In addition, the Ca²⁺ cations are observed to be linked with seven and eight O atoms to form CaO₇ and CaO₈ polyhedra. The substitution of one Sr²⁺ for two Na⁺ enables the construction of Na-doped SCLP with varying doping concentrations. As illustrated in Fig. 5b–d, the introduction of Na⁺ ions into SCLP can effectively modulate the proportions of SrO₉, SrO₈ and SrO₆ polyhedra, and the theoretically calculated proportions with variation of Na⁺ doping concentration are listed in Table 2. In detail, as the Na⁺ concentration increases, the proportion of the SrO₉ polyhedron decreases from 20.8% to 6.7%, while the proportion of the SrO₆ polyhedron increases from 6.3% to 24.5%. Simultaneously, the proportion of the SrO₈ polyhedron remains almost unchanged.

Fig. 5 The optimized crystal structure configurations of (a) SCLP and Na-SCLP with different Na⁺ concentrations of (b) 2.1 mol%, (c) 4.2 mol% and (d) 6.25 mol% based on DFT theoretical calculations. (e) Configurational coordinate diagrams to illustrate the PL wavelength tuning via Na⁺ doping. Gaussian multi-peak fitting and the related coordination environments of Eu²⁺ ions are also provided.

Table 2 Theoretically calculated proportions of SrO₉, SrO₈ and SrO₆ polyhedra in Na-SCLP samples doped with different amounts of Na⁺ ions

Na^+ content	0	2.1 mol%	4.2 mol%	6.25 mol%
SrO9	20.8%	10.6%	8.7%	6.7%
SrO8	72.9%	74.5%	71.7%	68.8%
SrO6	6.3%	14.9%	19.6%	24.5%

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Considering their similar ionic radii and the same valence between Eu²⁺ and Sr²⁺ ions, the added Eu²⁺ activators will substitute the Sr²⁺ cation site. In general, the 5d emitting peak position in energy (E, cm⁻¹) for Eu²⁺ ions in a specific coordination environment is proportional to the Eu²⁺ coordination number of (n) based on the following empirical equation:^43,44

where E₀ is a constant, V is the valence of the Eu²⁺ ion, E_a represents the electron affinity of ligand anions in eV, and r is the ionic radius of the Sr²⁺ ion. Accordingly, the Gaussian multi-peak fitted green, yellow and red emission bands can be assigned to Eu²⁺ activators located in the SrO₉, SrO₈ and SrO₆ polyhedra, respectively. As evidenced in Table 2, the introduction of Na⁺ ions will lead to a decrease in the proportion of SrO₉ but an increase in the proportion of the SrO₆ polyhedron. As a consequence, the number of Eu²⁺ activators in SrO₉ will be reduced while that in SrO₆ is increased. In this case, as illustrated in Fig. 5e, the population of Eu²⁺ ions in the high-energy state and low-energy state will be altered upon Na⁺ doping, which can well explain the red-shifting of the Eu²⁺ PL band from 520 nm to 550 nm with increasing Na⁺ concentration in the SCLP host. In addition, it can be well discerned form the configurational coordinate diagrams that low-energy (or long-wavelength) emission has a lower activation energy than high-energy (or short-wavelength) emission. Therefore, the long-wavelength emission is more easily quenched than the short-wavelength emission via non-radiative relaxation from the 5d excited state to the 4f ground state as a result of the crossover between 5d and 4f states in the configurational coordinate diagram. As a result, long-wavelength PL thermal quenching leads to FWHM narrowing, which outweighs the PL broadening owing to electron–photon coupling. Therefore, abnormal spectral narrowing is observed with elevation of temperature in the present SCLP and Na-SCLP materials because of multiple cation sites for Eu²⁺ emitting centers.

Finally, wLED devices were fabricated by combining a 410 nm violet chip with the blue Eu:BAM, the as-prepared green–yellow Eu:Na-SCLP and the red Eu:CASN phosphors to demonstrate their potential application in lighting. The ratios of three kinds of phosphors remained the same for all the wLEDs. The EL spectra and photographs of the fabricated wLEDs at the driven current/voltage of 100 mA/3 V are provided in Fig. 6a. Typical blue, green, yellow, and red emissions are observed for all the devices, leading to bright full-spectrum white light emitting with chromaticity coordinates located in the white region (Fig. S6†). Interestingly, compared to the case of Eu:SCLP based wLED, the EL spectra of Eu:Na-SCLP based device can cover the yellow gap between green and red, which results in significant improvement of the R10 index (above 95, Fig. S7†). Accordingly, the CRI value of R_a increases from 89 up to 98 and the special CRI values of R1–R15 all exceed 90 for the Eu:Na-SCLP-based devices (Fig. 6b), confirming that the fabricated wLEDs can be used for full-spectrum lighting. In addition, the associated LE and CCT are ∼50 lm W⁻¹ and ∼4000 K, respectively. The normalized EL spectra of a typical wLED at different currents are almost unaltered, as shown in Fig. S8,† indicating the excellent color stability of our designed full-spectrum lighting device. Here, it has to be mentioned that the value of R10 can reach an amazing 97 due to the efficient yellow emission from the Eu:Na-SCLP phosphor, which can greatly improve the ability to display real color and cause a more lifelike visual effect. In order to demonstrate the practical application of the as-prepared phosphors in full-spectrum lighting, the pictures obtained under the illumination of a series of wLEDs are presented in Fig. 6c. The images of fruits show warmer tones as well as a more comfortable visual feel compared to Eu:SCLP based wLED. All these results demonstrate that the as-prepared green–yellow Eu:Na-SCLP phosphors with violet-chip-excitable tunable spectral features have an outstanding potential for high-CRI full-spectrum solid-state lighting.

Fig. 6 (a) EL spectra of the fabricated wLEDs using Eu:BAM, Eu:Na (0–4 mol%)-SCLP and Eu:CASN phosphors. (b) R_a and R1–R15 values of the corresponding wLEDs, and (c) the display images using the wLEDs for lighting.

Conclusions

In summary, we have successfully incorporated Na⁺ dopants (up to 10 mol%) into SCLP crystal lattice to tune Eu²⁺ emission via modifying local ligand fields. With increasing Na⁺ concentration, the Eu:SCLP phosphor shows a gradual red-shifting of the PL band from 520 nm to 550 nm without obviously reduced PLQYs, accompanied by an elongated decay lifetime and broadened emitting bandwidth. All these results are attributed to the varied fractions of multiple cation sites for Eu²⁺ activators, which is further confirmed via first-principles DFT calculations. Finally, a series of wLEDs are fabricated by coupling the as-prepared Eu:Na-SCLP green–yellow phosphors and commercial blue/red phosphors with a violet chip, which can produce full-spectrum lighting with an ultra-high CRI R_a of 98 and special CRI R10 of 97.

Author contributions

D. C. initiated and designed the experiments, and L. Y., F. Y., T. P., X. P., S. W., S. J., and Y. F. performed the experiments collectively. X. P., Y. F., and D. C. conceived and supervised the research. All authors discussed the results and commented on the manuscript.

Conflicts of interest

There are no conflicts to declare.

Acknowledgements

This research was supported by the National Key Research and Development Program of China (2021YFB3500503), the National Natural Science Foundation of China (52272141, 51972060, 12074068, 52102159 and 22103013), and the Natural Science Foundation of Fujian Province (2022J05091, 2020J02017, 2021J06021, 2021J01190 and 2020J01931).

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Footnote

† Electronic supplementary information (ESI) available. See DOI: https://doi.org/10.1039/d3qi02377j

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