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View Article OnlineView Journal | View Issue

Color tuning of B

aCollege of Materials and Chemistry, China J

China. E-mail: din@cjlu.edu.cnbSichuan College of Architectural TechnologcDepartment of Physics, Sichuan University

Sichuan, P. R. China. E-mail: superman_mi

Cite this: RSC Adv., 2020, 10, 25500

Received 27th April 2020Accepted 10th June 2020

DOI: 10.1039/d0ra03793a

rsc.li/rsc-advances

25500 | RSC Adv., 2020, 10, 25500

i3+-doped double-perovskiteBa2(Gd1�x,Lux)NbO6 (0 # x # 0.6) solid solutioncompounds via crystal field modulation for whiteLEDs

Xufang Tang,a Dingfeng Jin,*a Jun Zhaob and Min Jin *c

Nowadays, rare-earth-free color-tunable solid solutions are receiving great attention. Here, we synthesize

a type of double-perovskite Ba2(Gd1�x,Lux)NbO6:Bi3+ (0 # x # 0.6) solid solution compound using high

temperature solid state reaction. The structural phase purity and photoluminescence (PL) properties of

the samples are characterized by powder X-ray diffraction (XRD), density functional theory (DFT)

calculations, UV-visible diffuse reflectance spectroscopy and PL spectroscopy. Structural analysis shows

that all the samples are crystallized in the double-perovskite structure with a cubic space group of

Fm�3m. Moreover, with the increase of Lu3+ content, the XRD positions are gradually shifted toward

higher diffraction angles, indicating the shrinkage of the crystal lattice. Our PL results show that the

Ba2(Gd1�x,Lux)NbO6:Bi3+ solid solutions can show Bi3+ tunable emissions from 462 nm to 493 nm and

excitation peaks from 363 nm to 390 nm with the increase of Lu3+ content from 0 to 0.6, owing to the

crystal field modulation around the Bi3+ ion. In addition, the blue-shift of the host excitation peaks is also

observed, which is ascribed to the increase of bandgap energies (i.e., from 3.01 eV to 4.14 eV based on

the DFT calculations). Besides, due to the closer structural rigidity induced by the replacement of larger

Gd3+ ions with smaller Lu3+ ions, the Ba2(Gd1�x,Lux)NbO6:Bi3+ solid solutions show an increase of Bi3+

emission intensity and QE values followed by a subsequent decrease. As a result, the highest QE value,

which corresponds to Ba2Gd0.8Lu0.2NbO6:Bi3+, is 49%. Finally, by coating this optimal blue phosphor and

the red CsPb(Br0.4I0.6)3 phosphor on a commercial UV LED chip, a white LED device with a color

temperature (CT) of 3633 K, CIE value at (0.381, 0.379), color rendering index (CRI) of 78.4, and luminous

efficiency of 48 lm W�1 is achieved.

1. Introduction

In recent years, Bi3+-doped phosphors have received more andmore attention due to the crystal host-dependent Bi3+ photo-luminescence (PL) resulting from its electron conguration of[Xe]-4f145d106s2.1,2 So far, single Bi3+-doped phosphors can showemission colors from UV,3 blue,4 and green,5 to yellow.6,7

Besides, Bi3+ is also reported to serve as an energy transfersensitizer for rare-earth (RE) (e.g., Eu3+–Tb3+,4,8 Pr3+,9 and Sm3+

(ref. 10)) and non-RE (e.g., Mn4+ (ref. 11) and Cr3+ (ref. 12)) ionsto enhance the PL intensity of these RE and non-RE ions. Inaddition, this energy transfer can sometimes lead to the PLtuning due to the combination of the emissions of the Bi3+ andRE or non-RE ions.4,8,9,11 Nowadays, tunable solid solutions play

iliang University, Hangzhou 310018, P. R.

y, Deyang 618000, P. R. China

, Huanlu Nan No. 21, Chengdu 610041,

njin@163.com

–25508

an important role in the lighting eld because they can emita desirable wavelength for device design but other factorsshould also be considered, such as the different responses ofdifferent phosphors to the same LED chip temperature.13 Thus,exploring tunable solid solutions is receiving great attention.Although some Bi3+ doped tunable solid solutions14–17 havebeen reported, their numbers are still very rare and need to beincreased.

Nowadays, perovskite-typed crystals used for white LEDs arehot research topic.18–25 As an important type of inorganicmaterials, the double-perovskite crystals with the structuralcomposition of (A2BB0O6) can have good electrical and opticalproperties.22,23 Depending on the A, B and B0 atoms, they canshow different crystal hosts for different RE and non-RE ionsdoping such as Bi3+–Mn4+,22 Eu3+,23,24 and Pr3+.25 Among them,Huang et al.22 reported that the co-substitution of the Gd3+/Nb5+

ions with the Bi3+/Mn4+ ions in the Ba2GdNbO6 crystal hostcould lead to the emission tuning, but the tunable solid solu-tions using the Ba2GdNbO6 as the starting host and the Bi3+ ionas the luminescent center are still not reported.

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In this work, we reported a new type of Ba2(Gd1�x,Lux)NbO6:Bi

3+ (0 # x # 0.6) solid solutions that can show the Bi3+

emission tuning from 462 nm to 493 nm and Bi3+ excitationtuning from 363 nm to 390 nm as the x value is increased from0 to 0.6. To reveal the reason of this spectral tuning, we carriedout the DFT calculations, UV-vis reectance and PL spectralmeasurements. Results and discussions are shown below.

2. Synthesis, characterization, andDFT calculations

Here, a series of Ba2(Gd1�x,Lux)NbO6:Bi3+ (x ¼ 0, 0.1, 0.2, 0.3,

0.4, 0.5, and 0.6) solid solutions were prepared using the hightemperature solid-state reaction method, and the raw chemicalmaterials were BaCO3 (analytical reagent), Gd2O3 (99.9%),Lu2O3 (99.99%), Nb2O5 (99.9%), and Bi2O3 (99.98%). Thedoping content of Bi3+ ion is 0.01, which is from Huang et al.22

Firstly, the reagents were weighed according to the abovechemical composition, and milled in an agate mortar for 1 h.Then, the mixed powders were red in an oven at 1200 �C for 5 hin air. Finally, aer re-milling for 15 min aer cooling to roomtemperature, we achieved the required solid solutions.

The powder X-ray diffraction (XRD) and PL spectra of theBa2(Gd1�x,Lux)NbO6:Bi

3+ samples were recorded on a powderdiffractometer used a Cu Ka irradiation source of l ¼ 1.5406 A,tube voltage of 36 kV, and tube current of 20 mA, and a HitachiF-7000 uorescent spectrophotometer equipped with a mercurylamp as the excitation source, respectively. The UV-vis reec-tance spectra, quantum efficiency (QE) yields, and electrolu-minescence (EL) performances of the LED device were recordedusing the UV-2550 PC UV-vis spectrometer (Shimadzu Corp.,

Fig. 1 (a) XRD patterns of Ba2(Gd1�x,Lux)NbO6:Bi3+ (x¼ 0, 0.1, 0.2, 0.3, 0.

is also indexed; (b) enlarged XRD patterns in the range of 29–31�; (c) Lu3

lattice, and lattice parameters of a(b)(c), and V.

This journal is © The Royal Society of Chemistry 2020

Japan), C9920-02 quantum yield system (Hamamatsu PhotonicsK. K., Japan), and StarspecSS-P6612 spectrometer, respectively.

The rst-principle calculations on the Ba2(Gd1�x,Lux)NbO6:Bi

3+ (x ¼ 0, 0.1, 0.2, 0.3, 0.4, 0.5, and 0.6) solid solutionswere performed within the framework of DFT using the Viennaab initio simulation package (VASP),26 with a kinetic energycutoff of 400 eV for the plane wave basis set expansion and 2p�0.1 A�1 k-spacing to sample the Brillouin zone. Lattice dynam-ical properties and bandgap energies were calculated using theprojector-augmented plane–wave (PAW) potentials27 with thegeneralized gradient approximation (GGA) of Perdew–Burke–Ernzerh of parameterization.28

3. Results and discussion

The XRD patterns of Ba2(Gd1�x,Lux)NbO6:Bi3+ (x ¼ 0, 0.1, 0.2,

0.3, 0.4, 0.5, and 0.6) solid solutions are shown in Fig. 1. It isobvious that all XRD positions of the samplesmatch with that ofICSD le no. 43760, indicating that the addition of the Bi3+ ionsand the change of the Gd3+ and Lu3+ ratios in the Ba2(Gd1�x,Lux)NbO6:Bi

3+ solid solutions do not induce the change of phasepurication (Fig. 1a). Hence, we achieve the aimed solid solu-tions. As depicted by the XRD range of 29–31� (where the (011)plane is in this range, and its diffraction intensity is the stron-gest line), the XRD peaks are gradually shied to higher angle asthe Lu3+ content is increased from 0 to 0.6, the diffraction angle,(Fig. 1b), indicating that the change of the Gd3+ and Lu3+ ratioinuences the crystal lattice but can keep the phasepurication.

To explain the XRD peak shiing, we draw the crystalstructure of the starting crystal Ba2GdNbO6, as shown in Fig. 2.

4, 0.5, and 0.6) solid solutions, where the peak of each diffraction plane+ content dependent d spacing values between the planes in the atom

RSC Adv., 2020, 10, 25500–25508 | 25501

Fig. 2 (a–c) Crystal structural pattern of Ba2GdNbO6, which is derived from the ICSD no. 43760. In this figure, gray, green, and red spheresdenote the Gd/Nb, Ba, and O atoms, respectively. The coordination environments of Gd/Nb and Ba cations are also given, as seen in (d).

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In this gure, we can see that the A, B and B0 are related to theBa, Gd, and Nb atoms, which are coordinated with 12, 6, and 6oxygen atoms, respectively. When considered the Gd3+ ions arereplaced by the Lu3+ ions, the Lu3+ ions are also coordinatedwith 6 oxygen atoms. According to the previous works,22,24,25 wecan know that the radii of Ba2+, Gd3+, Lu3+, and Nb5+ ions are1.61 A, 0.938 A, 0.861 A, and 0.64 A, respectively. On one hand,since the radius of the Bi3+ ion at six coordination number is1.03 A while the Ba2+ ion is located in the interstitial voidbetween octahedra, the Bi3+ ions tend to substitute the Gd3+

ions rather than the Ba2+, Lu3+, and Nb5+ ions. On the hand, theionic radii and charge differences between the Bi3+ and Ba2+/Lu3+/Nb5+ ions are larger than that between the Bi3+ and Gd3+

ions. In this case, when the Bi3+ content is xed (i.e., 0.01), theshrinkage of lattice cells, as shown by taking the spacing plane(011) as an example, appears with the substitution of larger Gd3+

ions with smaller Lu3+ ions. As a result, based on the equationof nl ¼ 2d sin q14–16,29,30 (where n is an integer, l is the wave-length of incident X-ray, d is the spacing between the planes inthe atom lattice, and q is the angle between the incident XRD rayand the scattering planes), when the n and l are xed, the

25502 | RSC Adv., 2020, 10, 25500–25508

decrease of d values leads to the increase of the values fromsin q, thereby shiing the XRD peak to higher angle. Moreover,according to the Vegard law, we also calculated the latticeparameters a(b)(c), and cell volume (V), as shown in Fig. 1c. Inaddition to the spacing d values, it is obvious that the latticeparameters a(b)(c), and cell volume V are also decreased with theincrease of the Lu3+ content, indicating the shrinkage of thelattice cell. Due to this regular change of the crystal lattice, theregular change of the optical bandgaps energy and spectralproperties may appear.

The density of state (DOS) results of the Ba2(Gd1�x,Lux)NbO6:Bi

3+ (x ¼ 0, 0.2, 0.4, and 0.6) solid solutions are shown inFig. 3a. Clearly, the top of valence band (VB) and the bottom ofconduction band (CB) of the Ba2GdNbO6:Bi

3+ are composed ofthe Nb(4d) states and O(2p) states, respectively. However, forother compounds (namely, Ba2(Gd1�x,Lux)NbO6:Bi

3+ (x ¼ 0.2,0.4, and 0.6)), the top of the VB mainly consists of Gd(3d) statesand Bi(6p) states for the Ba2(Gd0.8,Lu0.2)NbO6:Bi

3+, and O(2p)states for the Ba2(Gd0.6,Lu0.4)NbO6:Bi

3+ and Ba2(Gd0.4,Lu0.6)NbO6:Bi

3+, but the bottom of the CB mainly consists of theGd(3d) states for Ba2(Gd0.8,Lu0.2)NbO6:Bi

3+, Bi(6p) states and

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Fig. 3 Density of state (DOS) results of Ba2(Gd1�x,Lux)NbO6:Bi3+ (x ¼ 0, 0.2, 0.4, and 0.6) (a); (b) Lu3+ (x) content dependent Eg values, where

curve 1 and curve 2 denote the values from the DFT calculations and UV-vis diffuse reflectance spectra, respectively; (c) diffuse reflectancespectra of Ba2GdNbO6 and Ba2GdNbO6:Bi

3+.

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Lu(5d) states for Ba2(Gd0.6,Lu0.4)NbO6:Bi3+ and Ba2(Gd0.4,Lu0.6)

NbO6:Bi3+. It is also shown in Fig. 3a that the contribution of the

Lu(5d) states to the CB ad VB appears with the increase of theLu3+ content. Based on our DFT calculations, we nd reveal thatreplacing the Gd3+ by Lu3+ ions increases the band-gap (Eg)energies from 3.01 eV to 4.14 eV (Fig. 3b). Our DFT results aresimilar to other Bi3+-doped solid solutions featured the increaseof Eg with the replacement of larger ions by smaller ions (e.g.,Sc(Vx,P1�x)O4:Bi

3+,15 Ba3�xSrxSc4O9:Bi3+,16 and YPxV1–

xO4:Bi3+).17

The UV-vis diffuse reectance spectra of Ba2GdNbO6 andBa2GdNbO6:Bi

3+ samples are shown in Fig. 3b. A strongabsorption band in the range of 250–310 nm appear in bulkBa2GdNbO6, which is due to the host absorption. In Ba2-GdNbO6:Bi

3+, another weak absorption band in the range of310–370 nm appears, which is assigned to the absorption of Bi3+

ions. Based on the reectance curve of Ba2GdNbO6, we obtainthe optical bandgap values using the Kubelka–Munk equation,31

F(RN) ¼ (1 � RN)2/2RN ¼ K/S, where parameters RN, K, and S

This journal is © The Royal Society of Chemistry 2020

are the reectance, absorption, and scattering co-efficiencies,respectively. As a result, with the relationship between theabsorption efficient a and bandgap Eg values,22,31 ahv ¼ C1(hv �Eg)

n/2 (where parameters C1, h, v, and n are the proportionalityconstant, Planck constant (h ¼ 4.14 � 10�15 eV s�1), lightfrequency and constant, respectively), the Eg value (5.34 eV) ofthis sample can be achieved. Similarly, the Eg values of theBa2(Gd1�x,Lux)NbO6:Bi

3+ solid solutions are obtained. The Lu3+

content dependent experimental and theoretical Eg values areshown in Fig. 3c. Obviously, these experimental Eg values withthe increase of the Lu3+ (x) content show the similar tendency.

The emission and excitation spectra of Ba2(Gd1�x,Lux)NbO6:Bi

3+ (x ¼ 0, 0.1, 0.2, 0.3, 0.4, 0.5, and 0.6) samples areshown in Fig. 4a and b. There is only one emission band of theBi3+ 3P1 / 1S0 transition, conrming that the obtained solidsolutions have only one crystal site (i.e., Gd3+) for the Bi3+

substitution. The emission position with the increase of theLu3+ content is shied from 462 nm to 493 nm. This result verifythe microenvironment around Bi3+ ions is regularly changed in

RSC Adv., 2020, 10, 25500–25508 | 25503

Fig. 4 Emission (a) and excitation spectra (b) of Ba2(Gd1�x,Lux)NbO6:Bi3+ (x¼ 0–0.6), where the excitation andmonitored emission wavelengths

are the maximum Bi3+ excitation and emission intensity of (b) and (a), respectively; (c) CIE chromaticity coordinates of all samples, which arecalculated basing on the emission spectra of (a); and (d) dependence of the Bi3+ emission (blue) and excitation (red) positions and the hostexcitation positions (black) on the Lu3+ content.

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the formation of the solid solutions. Upon monitoring at themaximum emission intensity, the excitation spectra of the solidsolutions can be achieved, and they consist of two broad yetoverlapping bands. Among them, the bands peaked at higherenergy are from the host absorption and the positions with theincrease of the Lu3+ content are slightly shied to shorterwavelength (the shiing range is not broad); other bandspeaked at lower energy are due to the Bi3+ 1S0 /

3P1 transitionand the positions are shied from 363 nm to 390 nm. For theformer positions tuning, it is consistent with the increase of Egvalues. Thus, they can be ascribed to the optical bandgapmodulation. However, since the Bi3+ ion is a type of ion sensitiveto its local microenvironment, the Bi3+ excitation and emissionpositions tuning can be ascribed to the modulation of crystaleld strength, as we will discuss below. The tunable emissionpositions are reected by the tunable CIE chromaticity coordi-nates, as shown in Fig. 4c. Obviously, the colors are tuned in theblue region, from deep blue to pale blue. Fig. 4d show thedependence of the excitation positions of the host and Bi3+ ions

25504 | RSC Adv., 2020, 10, 25500–25508

and Bi3+ emission positions on the Lu3+ content. A linear rela-tionship against the Lu3+ content is seen, meaning that the Bi3+

excitation and emission position can be achieved in the range of363–390 nm and 462–493 nm by adjusting the Lu/Gd ratios.

According to the previous works,14–16,30,31 the major reason forthe red-shi of the emission position of a given dopant in thesolid solutions is assigned to the crystal eld modulationcaused by the size mismatching of the replacement ions. Ingeneral, the crystal eld strength (Dq) of the doping ion ina given solid solution is expressed as below:16

Dq ¼ Ze2r4

6R5

where Z is the valence of the anion, e is the charge of an elec-tron, r is the radius of the d wave function and R is the distancebetween the central cation and its ligands. In the current Ba2(-Gd1�x,Lux)NbO6:Bi

3+ solid solutions, the ionic radius of Gd3+

ions is larger than that of Lu3+ ions. Due to the shrinkage of cellvolume, the distance of the Bi3+ and O2� ions becomes shorter

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Fig. 5 A schematic diagram for illustrating the red-shift of the Bi3+ excitation and emission positions and the blue-shift of the host excitationposition in the Ba2(Gd1�x,Lux)NbO6:Bi

3+ solid solutions, where ET denotes the energy transfer.

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when the Gd3+ ions are substituted by the Lu3+ ion. In this case,based on the above equation, the shorter Bi3+–O2� distanceleads to the larger Dq value and the stronger crystal eld

Fig. 6 (a) Dependence of Lu3+ (x) content on the quantum efficiency (QE0.6) upon excitation at the maximum excitation intensity; (b) fabricationBa2Gd0.8Lu0.2NbO6:Bi

3+ and CsPb(Br0.4I0.6)3; (c) EL spectrum of the whBa2Gd0.8Lu0.2NbO6:Bi

3+, and the red CsPb(Br0.4I0.6)3 crystals; and (d) thspectrum.

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strength. This enhanced crystal eld strength correspondsto the red-shi of Bi3+ emission position, as seen in ref. 14–18and 23.

) and relative emission intensity of the Ba2(Gd1�x,Lux)NbO6:Bi3+ (x¼ 0–

profile of white LEDs device, where the red and blue spheres denotesite LEDs device (inset) fabricated by a 385 nm UV LED chip, the bluee CIE chromaticity of the LEDs device, which is achieved by the EL

RSC Adv., 2020, 10, 25500–25508 | 25505

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The mechanistic diagram depicted in Fig. 5 can be used toexplain the above Bi3+ luminescence. Upon excitation with theexcitation wavelengths of Bi3+ ions, the Bi3+ electrons are liedfrom the 1S0 ground state to the 3P1,

3P2,1P1 excited states.

Then, the excited electrons relax from the 3P2 and 1P1 energylevel to the 3P1 energy level and come back the 1S0 groundenergy level followed by the generation of the Bi3+ emissions.Sine the crystal eld around Bi3+ ions is strengthened as theGd3+ ions are substituted by the Lu3+ ion, the lowest 3P1 state ofBi3+ ion is closer to its 1S0 ground state. In this case, the red-shiof Bi3+ emission positions appears. Moreover, the Bi3+ emissioncan be achieved when the excitation wavelengths are less315 nm (namely, the host excitation, e.g., under 290 nm exci-tation) (not shown here), which means that there is the energytransfer from the host to the Bi3+ ion. However, the bulksamples without Bi doping do not have the luminescence, sothere is no transition from the bottom of conduction band (CB)to the top of valence band (VB). Besides, since the host excita-tion energies (the blueshi of excitation position) are increasedwith the increase of the Lu3+ content, the bandgap energies areincreased, as reected by the enlarged VB and CB gaps.

In addition to the above PL spectral results, here we also havemeasured the QE of the Ba2(Gd1�x,Lux)NbO6:Bi

3+ (x ¼ 0–0.6)samples by exciting with the maximum Bi3+-excitation intensity.Although these samples show different QE values, but the highestQE value is 49% (Fig. 6a, black), relating to the Ba2Gd0.8Lu0.2-NbO6:Bi

3+ sample. Moreover, these QE values experience an initialincrease followed by a subsequent decrease. This QE variation issimilar to the emission intensity variation of Bi3+ ion (Fig. 6a, red).In a word, the improved emission intensity is observed in theBa2(Gd1�x,Lux)NbO6:Bi

3+ (x ¼ 0–0.6) solid solutions. Since theGd3+, Lu3+ and Bi3+ ions have the same valence and the content ofBi3+ ions (i.e., 0.01) is xed, this crystal lattice regulation can beassigned to the change of the Gd3+ and Lu3+ radii mismatching.Hence, the shrinkage of the crystal lattice induced by thereplacement of larger Gd3+ ions with smaller Lu3+ ions induces thecloser structure rigidity, leading to the enhanced emission of Bi3+

ions. However, once the distance of the Bi3+ ions is too close, therelative Bi3+ concentration in a given lattice volume is increased,which leads to the PL quenching from the Bi3+ ions themselves.This increase and decrease progress of the PL intensity is similar tothe dopant-content induced PL quenching. In the previousworks,16,22,30 several RE and non-RE doped solid solutions can showthe improved emission intensity of these RE and non-RE ion.Importantly, the excitation peak of the Ba2Gd0.8Lu0.2NbO6:Bi

3+

sample is located at 388 nm, which matches with the commercialUV LED chip with the emission range at around 385–400 nm.Hence, we use this UV-converted blue-emitting sample to provethe application of the as-obtained solid solutions for the whiteLEDs by combining the red CsPb(Br0.4I0.6)3 perovskite crystals re-ported byref. 32. The fabrication patterns, EL spectrum, keyparameters, photographs and CIE chromaticity of this white LEDdevice are shown in Fig. 6b–d. Our measurements show that thisLED device show the white-emitting color, with the CIE chroma-ticity coordinates at (0.381, 0.379). The related CT, CRI, andluminous efficiency are 3633 K, 78.4, and 48 lm W�1, respectively,proving the potential application for white LEDs.

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4. Conclusion and perspectives

In this work, the double-perovskite Ba2(Gd1�x,Lux)NbO6:Bi3+

tunable solid solutions are synthesized using the high tempera-ture solid-state reaction. Structural analysis reveals that the as-obtained tunable solid solutions are crystallized in a cubicstructure with the space group of Ia3d (No. 230). Due to the radiidifference between the Gd3+ and Lu3+ ions, the XRD positionswith the increase of Lu3+ (x) content shi to higher diffractionangle, leading to the change of lattice parameters a(b)(c) and theshrinkage of cell volume (V). The electronic Eg bandgaps energies,evaluated basing on the DFT calculations and UV-visible diffusereectance spectra, are increased with the increase of Lu3+ (x)content, leading to the shiing of the host excitation positions toshorter wavelength (i.e., higher energy). In addition, with theincrease of Lu3+ content, we nd that the Bi3+ emission andexcitation positions are tuned from 462 nm to 493 nm and363 nm to 390 nm, respectively, which are assigned to the crystalstrength eld modulation around Bi3+ ions. Moreover, theenhanced Bi3+ emission intensity and QE values, possibly causedby the closing structure rigidity, is also observed, where theBa2Gd0.8Lu0.2NbO6:Bi

3+ is the optimal sample. Based on thisBa2Gd0.8Lu0.2NbO6:Bi

3+ blue sample and red CsPb(Br0.4I0.6)3perovskite crystals and a 385 nm UV LED chip, we fabricatea white LED device that can show the CIE coordinates at (0.381,0.379), color rendering index (CRI) of 78.4, color temperature(CT) of 3633 K, and luminous efficiency of 48 lm W�1. In addi-tion, the Ba2(Gd1�x,Lux)NbO6:Bi

3+ perovskites are oxygen-contained perovskites, which can exhibit the moisture-inducedPL quenching and structural instability much better than thoseoxygen-free perovskites such as the CsPb2Br5,18 CsPbBr3,19

CsPbBr1.5Cl1.5,20 and so on. Moreover, although some of oxygen-contained perovskites, such as Ba2GdNbO6:Bi

3+,Mn4+,22 La2-ATiO6:Bi

3+,Mn4+ (A¼Mg,Zn),30 and La2(Znx,Mg1�x)TiO6 (0# x#1):Bi3+,31 are also reported, our luminous parameters are better orcomparable to theirs. More importantly, the Ba2(Gd1�x,Lux)NbO6:Bi

3+ solid solutions contain the non-toxic metals (e.g., Pb),which could have less bad inuence on the environment andhuman heath. All in all, this work reports a new type ofperovskite-typed Bi3+-doped tunable solid solutions, which canhave the potential application for the white LEDs,33,34 and thebuilding lighing.35,36 Futhermore, this work can also give clues toother elds, such as the use of the light to address the environ-mental problems, such as the degradation of antibiotic mate-rials,37 organic materials,38 and the treatment of wastewater,38

acid water.39

Conflicts of interest

There are no conicts to declare.

Acknowledgements

This work is funded by the project of Natural Science Founda-tion (no. 18zx7125) from Southwest University of Science andTechnology.

This journal is © The Royal Society of Chemistry 2020

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