Zero-thermal-quenching of Mn4+ far-red-emitting in LaAlO3 perovskite phosphor via energy compensation of electrons' traps

Journal Pre-proofs Zero-thermal-quenching of Mn4+ far-red-emitting in LaAlO3 perovskite phosphor via energy compensation of electrons' traps Shuangqiang Fang, Tianchun Lang, Tao Han, Jinyu Wang, Jiayao Yang, Shixiu Cao, Lingling Peng, Bitao Liu, Alexey N. Yakovlev, Vladimir I. Korepanov PII: DOI: Reference:

S1385-8947(20)30288-6 https://doi.org/10.1016/j.cej.2020.124297 CEJ 124297

To appear in:

Chemical Engineering Journal

Received Date: Revised Date: Accepted Date:

10 December 2019 19 January 2020 31 January 2020

Please cite this article as: S. Fang, T. Lang, T. Han, J. Wang, J. Yang, S. Cao, L. Peng, B. Liu, A.N. Yakovlev, V.I. Korepanov, Zero-thermal-quenching of Mn4+ far-red-emitting in LaAlO3 perovskite phosphor via energy compensation of electrons' traps, Chemical Engineering Journal (2020), doi: https://doi.org/10.1016/j.cej. 2020.124297

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© 2020 Published by Elsevier B.V.

Zero-thermal-quenching

of

Mn4+

far-red-emitting

in

LaAlO3

perovskite phosphor via energy compensation of electrons' traps Shuangqiang Fanga,b,§, Tianchun Langa,b,§, Tao Hana,b,*, Jinyu Wanga, Jiayao Yanga, Shixiu Caoa, Lingling Penga, Bitao Liua, Alexey N. Yakovlevb, Vladimir I. Korepanovb. aChongqing

Key

Laboratory

of

Materials

Surface

&

Interface

Science,

Research Institute for New Materials Technology, Chongqing University of Arts and Sciences, Ch ongqing, 402160, China bSchool

of Advanced Manufacturing Technologies, National Research Tomsk Polytechnic

University, Tomsk, 634050, Russia §

Shuangqiang Fang and Tianchun Lang contributed equally to this work

E-mail address: [email protected] (T. Han) ARTICLE

INFO

Keywords: Zero-thermal-quenching, high quantum efficiency, Ca2+, Bi3+ and Mn4+ co-doped, LaAlO3 phosphor, spectrum resemblance to phytochrome ABSTRACT: Nowadays, Mn4+-doped oxide phosphors have attracted more and more attentions owing to their widespread applications in white LEDs, optical data storage and agricultural production, but these phosphors have two most significant problems including thermal quenching (TQ) and low quantum efficiency. Here, we report a far-red-emitting LaAlO3:3%Ca2+,1%Bi3+,0.1%Mn4+ perovskite phosphor which exhibits zero-TQ even up to 150 ℃ and high internal quantum efficiency (IQE) of 89.3%. To our best knowledge, the zero-TQ phenomenon is first realized in Mn4+-activated perovskite phosphors caused by the synergistic action of Ca2+ and Bi3+ which is

1

attributed to the efficient energy transfer, energy compensation and structural rigidity enhancement. Moreover, the gratifying luminous performance improvement is obtained due to charge compensation effect, optimized crystal field and excited electrons transfer. The main emission peak of this phosphor is monitored at ~730 nm which perfectly matches the absorption spectrum of phytochrome PFR which has a good application prospect for improving plant seed germination, flowering, fruiting and aging. These findings may provide a feasible way to simultaneously improve thermal stability and quantum efficiency of Mn4+ luminescence in oxide hosts. 1. Introduction Mn4+ is known to activate red emission in many hosts and widely applied and extended values in white LEDs, backlight displays, holographic recording, optical data storage, laser application, thermoluminescence dosimetry and agricultural production [1-8], which has the potential to replace more expensive rare-earth activators, such as Eu3+, due to its broad excitation bands, sharp emission lines, abundant and cheap manganese raw materials [9,10]. As a luminescence center, Mn4+ can be efficiently activated in three kinds of host materials, namely, fluorides, oxides, and oxyfluorides [11]. As previous reports, Mn4+-activated fluorides and oxyfluorides often have good thermal stability [3,10], but the application of oxides phosphors are still hampered by the thermal quenching of the Mn4+ luminescence resulting in the loss of energy output which is usually attributed to the non-radiative relaxation of excited electrons to the ground state of the activator [12-14]. In LED devices, the temperature of the on-chip phosphor layer easily reaches 120 ℃. At elevated temperatures, the thermal quenching occurs for Mn4+-doped phosphors. For example, Sun et al. synthesized La2LiSbO6:0.3%Mn4+,1.6%Mg2+ far-red emitting

2

phosphors with a IQE of 92% under 338 nm excitation but only retain 58% at 150 ℃ of the initial value [15]. Liang et al. prepared CaLaMgSbO6:0.7%Mn4+ phosphor with 88% IQE upon excitation at 370 nm but it dropped to 54% when the temperature rose to 150℃ [16]. Our group summarized the temperature-dependent photoluminescence property of 63 species Mn4+-activated oxide phosphors and listed them in Table S1 which displays excitation wavelengths, integral emission intensities percentage at 150 ℃ (IPL150) and Mn4+-doped concentration. From the Table S1, only 6 species phosphors can keep over 90% emission output at 150 ℃ but 57 species phosphors cannot exhibit satisfactory thermal stability, even most of them only reserve less than 50% emission output, such as AGe4O9 (A=K2, K1.5Rb0.5 and Rb2) [S2], Ba2GdNbO6 [S5], BaMgAl10O17 [S10], Gd2ZnTiO6 [S20] and La3GaGe5O16 [S25]. Among these phosphors, no zero-TQ samples were reported. On the other hand, Ya Zhydachevskii prepared Mn4+-doped YAlO3 single crystal by Czochralski method and obtained zero-TQ property [7], Deng and Peng obtained the ultrastable red-emitting phosphor-in-glass (PiG) consisting of 3.5MgO·0.5MgF2·GeO2:Mn4+ phosphor in a glass matrix [17,18], but note that these samples are the crystal or PiG not the powders. The reason for this phenomenon is attributed to a high thermal conductivity to transfer the heat from luminescence center to the crystal or PiG which is beneficial for improving the thermal stability. Nevertheless, this method is not an ideal path to obtain the robust thermal stability phosphor due to (i) the existence of degradation in the PL intensity and QE when the phosphor materials are transformed to PiG; (ii) the mismatching of the refractive index between the phosphor and the glass matrix; (iii) the absorption of light by the glass matrix and poor transparency of PiG [19-21]. Thus, how to obtain a Mn4+-activated oxide phosphor with excellent thermal stability or even zero-TQ at 150 ℃ is still an unsolved problem.

3

Since Kim's group firstly reported a zero-TQ Na3-2xSc2(PO4)3:xEu2+ phosphor and explained the mechanism that zero-TQ originates from the compensation of emission losses due to the polymorphic nature of the host and the energy transfer from traps consisting of the electron-hole pairs to the excited state energy levels of activator and leading to radiative recombination [22], the designs of zero-TQ phosphors attracted intense concern of many research groups. The subsequent studies mainly focused on Eu2+-activated oxides, nitrides, and phosphates, including Sr3SiO5:Eu2+ [14], BaAl12O19:Eu2+ [23], Na3RbMg7(PO4)6:Eu2+ [24], SrLiAl3N4:Eu2+ [25] and NaAlSiO4:Li+,Eu [26]. The other available path to obtain small thermal quenching phosphors is by introducing another rare earth or transition metal elements to act as an electrons' donor to compensate the emission loss and suppress TQ process, such as BaMgP2O7:Eu2+,Mn2+ [27], Ca3Y(PO4)3:Eu2+,Mn2+ [28], LuVO4:Bi3+,Eu3+ [29], Zn3(BO3)(PO4):Mn2+,Tb3+ [30], and Sr8ZnY(PO4)7:Tb3+,Eu3+ [31]. To our best knowledge, although there are the synthesized zero-TQ Eu-doped phosphors, surprisingly only

two

zero-TQ

Mn4+-doped

oxide

phosphors

were

reported

(Mg4GeO6:Mn4+

and

6MgO·As2O5:Mn4+) in seventy years ago which were used in the high pressure mercury lamps [32,33]. At present, the main method to enhance the thermal stability for Mn4+-activated oxide phosphors is the substitution by the smaller cations to suppress cell volume and superior lattice rigidity or putting phosphors in glass, which have various disadvantages [17,34-35]. Inspired by the zero-TQ mechanism of Eu2+-activated phosphors and considering the charge compensation and optimizing crystal field effect of Ca2+ and possible energy transfer between Bi3+ and Mn4+ [36-38], we introduced Ca2+ and Bi3+ into LaAlO3:Mn4+ to increase the depth and density of electron traps and raise the probability of capturing electrons in the energy transfer process, so as to improve the thermal stability. The phase composition, crystal structure,

4

luminescence properties, energy transfer mechanism, TQ mechanism and the application of this phosphor were investigated in details. Impressively, we found that by incorporating of Ca2+ and Bi3+, not only the luminescence properties of Mn4+ is obviously improved, but also the TQ process is efficiently suppressed. The synthesized LaAlO3:3%Ca2+,1%Bi3+,0.1%Mn4+ phosphor has a high IQE of 89.3% and zero-TQ up to 150 ℃. Importantly, the method of co-doped smaller cations and energy donors in host may be a feasible way to improve thermal stability of Mn4+-activated oxide phosphor. Finally, the characteristic far-red-emitting of LaAlO3:3%Ca2+,1%Bi3+,0.1%Mn4+ shows a perfect match with the absorption of phytochrome PFR and exhibits a good application prospect for improving plant seed germination, flowering, fruiting and aging. 2. Experimental section 2.1. Materials and sample synthesis Ca2+, Bi3+ and Mn4+ co-doped LaAlO3 was synthesized through the high-temperature solid-state reaction. La2O3 (99.99%), Al2O3 (A.R.), Bi2O3 (99.99%), MnCO3 (A.R.), CaCO3 (A.R.) were used as raw materials. According to the composition, stoichiometric of the above raw materials were weighted and transferred in to an agate mortar. Ethanol was added for dispersion adequately. Then, the mixtures were ground thoroughly and dried in oven at 70 ℃. After that, these powders were heated at 800 ℃ for 2 h and further sintered at 1550 ℃ for 5 h. After cooled down to room temperature, the block solid was ground to fine powders for further analysis. 2.2. Characterization The crystal structures were identified by an X-ray diffractometer (XRD-6000, SHIMADZU) with Cu Ka radiation (λ=1.5405 Å) in range of 2θ=10-80 with a step angle of 0.08°, tube voltage of 30 kV and tube current of 20 mA. GSAS program was used to do the structure refinement.

5

Morphologies were observed by a high resolution transmission electron microscopy (HRTEM) analyses (JEM-21000, JEOL, Japan). Photoluminescent (PL), PL excitation spectra (PLE) and quantum efficiency were recorded by using a fluorescence spectrophotometer (F-7000, Hitachi, Japan) with a 150 W xenon lamp at room temperature, Al2O3 as a reference material was used to measure quantum efficiency. The quantum yields can be calculated using the following equations [39]:

 int 

I em  LS  I abs  E R   E S

(1)

 ext   int  abs  abs 

(2)

 ER   ES  ER

(3)

where ES and ER are spectra of excitation light with and without the sample in the integrating sphere, LS is the emission spectrum of the sample, and ξabs is the absorption effciency. Temperature-dependent luminescence property was measured by a FLS980 spectrometer (Edinburgh Instruments, the United Kingdom) with a 450 W Xe lamp as the excitation source. UV-vis absorption spectra were obtained by a U-3310 spectrophotometer (Hitachi, Japan). Lifetimes of the prepared samples were measured by a FLS920 spectrometer (Edinburgh, UK) equipped with a nanosecond flash lamp as the excitation source. The temperature-dependent decay curves were detected by the same spectrometer equipped with a TAP-02 high temperature fluorescence

accessory

(Tian

Jin

OrienteKOJI

Instrument

Co.,

Ltd.,

China).

The

thermo-luminescence (TL) spectra were monitored by a FJ-427A TL meter (Beijing Nuclear Instrument Factory) with a heating rate of 1 ℃/s after the samples were exposed under 368 nm excitation for 10 minutes.

6

2.3. LED fabrication The LED was fabricated by a mixture of the transparent silicone resin, obtained phosphors and NUV chip. After vacuum treatment to remove the air bubbles, the mixture was coated on the lead frame and subsequently heated at 100℃ for 1 h and 150℃ for 3 h. After heating, LED device was obtained. 3. Results and discussion 3.1. Structure identification and mechanism of Ca2+, Bi3+, Mn4+ co-doping XRD patterns of LaAlO3:1%Bi3+, LaAlO3:0.1%Mn4+ and LaAlO3:xCa2+,1%Bi3+,0.1%Mn4+ (x=0, 1%, 3%, 5%, 7% and 9%) are shown in Fig. 1a. Compared with standard PDF card, all diffraction peaks are well consistent with LaAlO3 (PDF#82-0478), demonstrating that the doped Ca2+, Bi3+, Mn4+ do not change the phase structure and successfully obtain the desired solid solution phosphors. Additionally, because of the smaller ionic radius of Ca2+ (0.99Å) replacing La3+ (1.06Å), the diffraction peaks of XRD are shift to large angle with the increase of Ca2+, which can also verify the incorporation of Ca2+ in LaAlO3 host. In order to investigate the structure disorder caused by Ca2+, Bi3+, Mn4+ co-doping, Rietveld refinements are performed. Typically, taking LaAlO3:3%Ca2+,1%Bi3+,0.1%Mn4+ for example, as displayed in Fig. 1b. The residual factors (Rp, Rwp, and χ2) of the refinement converge to low level, implying the reliable refinement results and phase purity. With the increase of Ca2+, the crystal cell parameters gradually decrease and reach minimum (a=b=5.336 Å, c=13.08 Å and V=322.53 Å3) when x=9% (Fig. 1c). The result strongly suggests that smaller Ca2+ has been successfully incorporated into the LaAlO3 matrix and a contracted crystal lattice has been obtained as expected. To confirm the substitution location of Ca2+, Bi3+ and Mn4+ in LaAlO3, according to the defect chemistry, an

7

acceptable percentage difference in ionic radius between the doped and substituted ions should be not exceed 25% [40]. The substitution relation can be inferred from the following equation [41]: Dr  100 

R m CN   Rd CN 

(4)

Rm CN 

Dr is the radius percentage discrepancy. Rm and Rd are the radii of the host cation and doped ion, respectively. As we know, the ionic radii of Ca2+ (r = 0.99 Å) and Bi3+ (r = 1.03 Å) are more similar to La3+ (r = 1.06 Å) and the values of the radius percentage discrepancy between La3+ and Ca2+, Bi3+ are 6.6% and 2.8% which are much less than the limitation value, so the sites of La3+ are substituted by Ca2+ and Bi3+ . In the same principle, Mn4+ (r = 0.53 Å) displaces Al3+ (r = 0.535 Å) in unit cell and the schematic illustration of this substitution mechanism is displayed in Fig. 1d. (a)

2+

3+

(b)

4+

LaAlO3:xCa ,1%Bi ,0.1%Mn

2+

3+

4+

LaAlO3:3%Ca ,1%Bi ,0.1%Mn

x=9%

RP=6.89% Rwp=4.53%

x=7%

Obs Calc Bra peaks Diff

2

 =1.53

Intensity(a.u.)

Intensity(a.u.)

x=5% x=3% x=1% 4+

LaAlO3:0.1%Mn

3+

LaAlO3:1%Bi

PDF 82-0478 LaAlO3

10

20

30

40 50 2 Theta (Degree)

327.5

Lattice parameters

325.0

60

80 32 33 34 35

70

10

20

30

40 50 60 2 Theta (Degree)

70

80

Cell volume (V)

(c)

322.5 13.11

Cell parameters (c)

13.10 13.09 13.08

Cell parameters (a=b)

5.36 5.35 5.34 0

2

2+

4

6

Ca concentration(%)

8

Fig. 1. (a) XRD patterns of LaAlO3:1%Bi3+, LaAlO3:0.1%Mn4+ and LaAlO3:xCa2+,1%Bi3+,0.1%Mn4+ (x=0, 1%, 3%, 5%, 7% and 9%), the right pattern shows the enlarged XRD pattern between 2θ range of 32°-35°. (b) XRD

8

Rietveld refinement pattern of LaAlO3:3%Ca2+,1%Bi3+,0.1%Mn4+. (c) The variations of lattice parameter versus various Ca2+ doping concentration. (d) Schematic illustration of the substitution mechanism of Ca2+, Bi3+, Mn4+ to La3+ and Al3+ and effect of Ca2+ on the local crystal structures.

HRTEM analyses are further conducted to examine the particle crystallinity of the LaAlO3:3%Ca2+,1%Bi3+,0.1%Mn4+ phosphor, as given in (Fig. 2a, b). The phosphor has a smooth and even edge and well crystallized with fine lattice arrangement, and low structural defects. As shown in Fig. 2b, the crystal lattice spacing and the histogram of (012) plane are about 3.79 Å, which are consistent with the XRD results. The FFT (Fast Fourier Transform) pattern (the inset of Fig. 2b) shows the single crystal character of this phosphor grain. Fig. 2c shows the element mapping images and all elements distribute with uniform form in the image contours, matching well with the HRTEM image which prove the existence of Ca2+, Bi3+ and Mn4+ ions in the LaAlO3 host. Moreover, the EDS spectrum and composition analysis are also provided in Fig. 2c and Table S2 which demonstrate the actual composition is consistent with the chemical formula.

9

Fig. 2. (a), (b) HRTEM images of LaAlO3:3%Ca2+,1%Bi3+,0.1%Mn4+ phosphor and the inset is FFT transition pattern and histogram of lattice plane (012). (c) Element mapping images and EDS spectrum of LaAlO3:3%Ca2+,1%Bi3+,0.1%Mn4+ phosphor.

3.2 Photoluminescence properties PLE and PL spectra of LaAlO3:1%Bi3+, LaAlO3:0.1%Mn4+ and LaAlO3:1%Bi3+,0.1%Mn4+ are shown in Fig. 3a. LaAlO3:1%Bi3+ has two characteristic excitation peaks appearing at 305 nm and 368 nm when monitored at 418 nm, which are ascribed to typical 1S0→1P1 and 1S0→3P1 transition. Under 368 nm excitation, an obvious single blue-violet emission peak is observed at 418 nm, which is attributed to the energy radiative transition of 3P1→1S0. Two distinct excitation bands are observed in the PLE spectrum of LaAlO3:0.1%Mn4+. The strong broad band is in range from 270 to 440 nm and the full-width at half-maximum (FWHM) is 118 nm, which exhibits a

10

good adaptation for the near UV chips, the weak narrow one is in range from 470 to 500 nm. By Gaussian fitting, these two peaks are divided into four sub-bands peaking at 320, 356, 410 and 490 nm which are assigned to Mn4+ →O2- charge transfer of 4A2g → 4T1g, 4A2g → 2T2g and 4A2g → 4T2g transitions, respectively. Under 340 nm excitation, it shows a weak emission peak at 701 nm and a stronger one at 734 nm, due to the internal vibronic splitting from the characteristic 2Eg→4A2g transition of Mn4+ in [MnO6] octahedron. As shown in Fig. S1-3, the optimal Mn4+-doping concentration is determined by 0.1% and according to the Dexter energy resonance theory, the interaction type between Mn4+ ions can be ascertained belong to dipole-dipole interaction. Furthermore, because the emission peak of Bi3+ overlaps with the excitation peak of Mn4+, energy transfer process from Bi3+ to Mn4+ can occurs. Noteworthily, when Bi3+ and Mn4+ are co-doped in LaAlO3 host, we achieve similar PLE and PL spectra like the Mn4+ single-doped sample, but there is no Bi3+ emission under 368 nm excitation, only Mn4+ far-red emission is detected and the peaks blue-shift by 2 nm and 5 nm, respectively. This significant phenomenon proves the existence of Bi3+, Mn4+ in LaAlO3 matrix and their high efficient energy transfer. Fig. 3b shows the UV-vis absorption spectra of LaAlO3:0.1%Mn4+, LaAlO3:3%Ca2+,0.1%Mn4+, LaAlO3:1%Bi3+,0.1%Mn4+ and LaAlO3:3%Ca2+,1%Bi3+,0.1%Mn4+, respectively. Two absorption bands are range from 230 to 380 nm and 465 to 505 nm, which caused by characteristic absorption of Bi3+ and Mn4+. The absorption at 230-380 nm can be significantly improved by doping Ca2+ and Bi3+ attributed to the optimized crystal field effect, charge compensation effect and nephelauxetic effect, which lead to an enhancement of internal quantum yield. In order to obtain the more band structures' details, the optical band gaps are calculated based on the UV-vis absorption data. The corresponding equation is presented as follow [42]:

11

h n  Ah  E g 

(5)

where A, α, h, and ν stand for the constant, absorption coefficient, Planck constant, and frequency, respectively. Eg is the energy of band gap and n represents the direct or indirect transition while it equals to 2 or 1/2. On the basis of previous reports [43,44], 1/2 is used as the value of n to estimate the band gaps. As shown in Fig. 3b, according to the plot of (αhν)1/2 versus hν, the energies of these phosphors are calculated to be 2.92, 2.95, 3.02, and 3.08 eV, respectively, indicating that Ca2+ and Bi3+ doped can slightly increase the optical band gaps of LaAlO3:Mn4+ to provide a more suitable coordination environment. To investigate the influence of Ca2+ doping on the luminescence properties, the PL spectra of LaAlO3:xCa2+,0.1%Mn4+ (x=0, 1%, 3%, 5%, 7% and 9%) phosphors are measured as shown in Fig. 3c. The introduction of Ca2+ can drastically improve the luminous intensity by 218% than Ca2+-free sample (Fig. 3d) when x=3%. Mn4+ replaces Al3+ to form luminescence center [MnO6], meanwhile the substitution breaks the electroneutrality of compound (La3+-Al3+-La3+) and generates excess O2- vacancies to form the photon traps which suppress the luminescence of Mn4+. But by incorporating Ca2+, the unbalanced electroneutrality (La3+-Mn4+-La3+) turns into the balance (Ca2+-Mn4+-La3+=La3+-Al3+-La3+) and eliminates O2- vacancies, leading to enhance the emission of Mn4+. For quantitatively analyzing the effect of Ca2+ on the luminescence performance, the values of IQE are monitored under 340 nm excitation. As shown in Fig. 3e, the IQEs of LaAlO3:xCa2+,0.1%Mn4+ firstly increase and then decrease by x increasing from 52.8% to 73.1% which is consist with luminous intensity. In order to further analyze the effect of Ca2+ on energy levels and the nephelauxetic of Mn4+, the local crystal-field strength Dq and the nephelauxetic ratio β1 can be calculated by equation 6-9.

12

 

E 4T2g  10 Dq

(6)

2

   E     10 E      Dq  B  Dq   Dq  E  15  8  Dq   

(7)

   3.05C  7.90  1.80B

E 2 Eg B

B

 B  B0

1  

2

(8)

Dq

  C    C   0

   

2

   

(9)



Where E  E 4T1g 4 F  E 4T2 g , B0 is 1160 cm-1 and C0 is 4303 cm-1 [45,46]. Typically, LaAlO3:3%Ca2+,0.1%Mn4+ is chosen for example and the values of 4T1g, 4T2g, and 2Eg of are determined at 29412 cm-1, 20492 cm-1and 13661 cm-1. Therefore, the value of Dq, B, C, and β1 are calculated to be 2049 cm-1, 921 cm-1, 2337 cm-1, and 0.96, respectively. It can be reckoned that Dq/B is about 2.22 (Fig. 3f). For comparison, the Dq/B and β1 of Ca2+-free sample are calculated 2.49 and 0.91, indicating that Ca2+ can tune the Mn4+ surroundings close to the weak crystal field and offer a stronger nephelauxetic effect, which provides a comfortable condition for Mn4+ emission. Unlike the usual charge compensation mechanism of Mg2+ in LaAlO3 host [47], Ca2+ can supply the charge compensation for Mn4+ luminescence center, as well as optimize crystal field and electrons surrounding [MnO6] to promote the luminescence performance.

13

(b) 1

4 1

S0 P1

4

A2g T1g 1

4+

LaAlO3:0.1% Mn

1

S0 P3

2+

4+

3+

4+

LaAlO3:3%Ca ,0.1% Mn

3.08 eV

LaAlO3:1% Bi ,0.1% Mn 2+

3+

LaAlO3:3%Ca ,1%Bi , 4+

2.95 eV

200

690

700

(e)

73.1%

Internal quantum efficiency(%)

60

69.4%

400

500 600 Wavelength(nm)

700

800

2

3

4

5

Photo energy(eV)

6

A

3%

(d)

218%

68.2%

70

300

ex=340 nm

710 720 Wavelength(nm)

2.92 eV

380 nm 465nm 505nm

Relative intensity(a.u.)

Relative intensity(a.u.)

x=0 x=1% x=3% x=5% x=7% x=9%

3.02 eV

1/2

A2g T2g

230 nm

(c) LaAlO3:xCa2+,0.1%Mn4+

4

  h 

Absorption

0.1% Mn 4

730

740

65.2%

0

2

4 6 2+ Ca concentration(%)

8

10

63.6%

52.8%

50 40 30 20 10 0

0

2

4 6 2+ Ca concentration(%)

8

10

Fig. 3. (a) PLE and PL spectra of LaAlO3:1%Bi3+, LaAlO3:0.1%Mn4+ and LaAlO3:1%Bi3+,0.1%Mn4+. (b) UV-vis absorption

spectra

of

LaAlO3:0.1%Mn4+,

LaAlO3:3%Ca2+,0.1%Mn4+,

LaAlO3:1%Bi3+,0.1%Mn4+

and

LaAlO3:3%Ca2+,1%Bi3+,0.1%Mn4+. The right pattern is the fitting of the corresponding band gap energies of these phosphors. (c) PL spectra of LaAlO3:xCa2+,0.1%Mn4+ with the various value of x (x=0, 1%, 3%, 5%, 7% and 9%). (d) The Ca2+-dependent pattern on luminous intensity. (e) The histogram of the internal quantum efficiency of LaAlO3:xCa2+,0.1%Mn4+ (x=0, 1%, 3%, 5%, 7% and 9%) under 340 nm excitation. (f) Tanabe-Sugano 14

energy-level diagram of Mn4+ in an octahedral crystal field.

Although Ca2+ can obviously improve the IQE but it is not up to the practical requirement value of 90%. Thus, basing on the introduction presented reasons, Bi3+ is chosen to be a sensitizer for the further IQE enhancing. PL spectra of LaAlO3:3%Ca2+,yBi3+,0.1%Mn4+ (y=0, 0.6%, 0.8%, 1%, 1.2% and 1.4%) are shown in Fig. 4a. The luminescence intensity of Mn4+ exhibits a remarkable promotion and achieves as high as 185% when y=1%, but no Bi3+ characteristic emission is observed under 368 nm excitation. And under 340 nm excitation, Mn4+ emission intensity shows a similar trend and also achieves as high as 170%. The energy transfer efficiency from Bi3+ to Mn4+ can be calculated according to the equation 10:

T 

IS  I0 I0

(10)

where ηT represents the energy transfer efficiency, and IS and I0 stand for the emission intensities in the presence and absence of Bi3+, respectively. The values of energy transfer efficiencies for y = 0.6%, 0.8% and 1.0% are determined to be 79.5%, 83.5% and 90.9%, which show a high energy transfer efficiency from Bi3+ to Mn4+. However, a sharp emission fall occurs when Bi3+ exceeds 1% due to the strong concentration quenching effect, thus determining the optimal Bi3+-doped concentration is 1%. Ulteriorly, IQE of these samples are measured under 368 nm excitation and displayed in Fig. 4b, illustrating that the values of IQE gradually increases due to the energy transfer from Bi3+ to Mn4+ and reach up to 89.3% which is the brightest far-red phosphor to our best knowledge (Table 1). As Bi3+ continues to increase, IQE declines sharply owing to the following reasons. Firstly, a concentration quenching effect may occur when y>1%. Secondly, the La vacancy concentration may have been too high and significantly change the electronic-band structure and deteriorating the sensitization. Finally, the crystal field is not suitable for Mn4+

15

illumination and then deteriorate the far-red-light emission. To support the spectra analysis, the decay times of LaAlO3:3%Ca2+,yBi3+,0.1%Mn4+ (y=0, 0.6%, 0.8%, 1% and 1.4%) monitoring 732 nm emission bands are also investigated, as plotted in Fig. 4c. The data can be fitted with the second-order exponential decay mode, as the following expression [48]: I t   A1 exp t /  1   A2 exp t /  2   I 0

(11)

Where I(t) is the luminescence intensity at certain time t, A1 and A2 are constants, τ1 and τ2 are the rapid and slow times for the exponential components, respectively. The effective decay times can be approximately calculated as follow:



 *  A1 12  A2 22

 A 

1 1

 A2 2



(12)

Based on the above equation, the decay time are calculated 3.43, 3.51, 3.57, 3.65, and 3.39 ms corresponding to y=0, 0.6%, 0.8%, 1%, 1.2% and 1.4%, respectively. The appropriate introduction of Bi3+ can suppress the non-radiative transition of Mn4+ through the energy transfer, but excess Bi3+ will lead to the concentration quenching effect. This is strong evidence of Bi3+-Mn4+ energy transfer in LaAlO3:Ca2+,Bi3+,Mn4+ phosphor. The similar evidence was also obtained in the others previous reports, such as (Tb1-xMnx)3Al2(Al1-xSix)3O12:Ce3+ [49], Ba5Gd8Zn4O21:Yb3+/Tm3+ [50] and Y3Al5O12:Yb3+,Er3+,Ho3+,Cr3+ [51]. In order to further disclose the energy transfer process, the schematic diagram is shown in Fig. 4d. Mn4+ ions are activated from 4A2g to 4T2g, 2T2g, and 4T1g or even the conduction band, and after that the excited Mn4+ ions return to the 2E energy level and then reverted to 4A2g with the far-red light of 734 nm. In the other hand, Bi3+ ions are excited to 3P1, 3P2, 1P1 and the conduction band from 1S0 by UV radiation. Then, they relaxed to the excited state of 3P1. Meanwhile, the energy transfer occurs between Bi3+ and Mn4+ from 3P1 to 2E. There is no Bi3+ emission in the

16

Bi3+, Mn4+ co-doped sample and the obvious enhancement of Mn4+ emission, which shows an efficient energy transfer. In order to figure out the specific concentration quenching mechanism, the critical distance Rc of LaAlO3:3%Ca2+,1%Bi3+,0.1%Mn4+ which assess the average distance between the sensitizers and activators can be calculated using the following equation [52]:  3V  Rc  2    4xc N 

1

3

(13)

V, xc, N represent the volume of the unit cell, the critical concentration, and the number of available sites for the dopant in the unit cell. Herein, V=325.77 Å3, N = 2, and xc = 0.011, then Rc is calculated to be 30.47 Å which is far away from the limitation value of 5 Å, implying that the concentration quenching is mainly dominated by the electric multipolar interaction. 100

ex=340 nm ex=368 nm

90 Internal quantum efficiency(%)

y=0 y=0.6% y=0.8% y=1.0% y=1.2% y=1.4%

Intensity of 732 nm peak(a.u.)

Relative intensity(a.u.)

(a) LaAlO3:3%Ca2+,yBi3+,0.1%Mn4+ ex=368 nm 1%

170%

185%

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

3+

Bi concentration(%)

2+

3+

4+

Logarithmic intensity(a.u.)

LaAlO3:3%Ca ,yBi ,0.1%Mn

85%

88.6% 89.3%

73.1%

69.5% 68.2%

70 60 50 40 30 20 10 0

420 450 480 510 540 570 600 630 660 690 720 Wavelength(nm)

(c)

80

(b)

0.0

0.2

0.4 0.6 0.8 1.0 3+ Bi concentration(%)

1.2

1.4

=3.43 ms y=0 =3.51 ms y=0.6% =3.57 ms y=0.8% =3.65 ms y=1.0% =3.39 ms y=1.4%

2

6 4 Decay time(ms)

8

Fig. 4. (a) PL spectra of LaAlO3:3%Ca2+,yBi3+,0.1%Mn4+ with the various values of y (y=0, 0.6%, 0.8%, 1%, 1.2% and 1.4%). (b) The IQE histogram of LaAlO3:3%Ca2+,yBi3+,0.1%Mn4+ (y=0, 0.6%, 0.8%, 1%, 1.2% and 17

1.4%) under 368 nm excitation. (c) Decay curves of LaAlO3:3%Ca2+,yBi3+,0.1%Mn4+ (y=0, 0.6%, 0.8%, 1% and 1.4%) under excitation at 368 nm and monitoring at 732 nm. (d) Energy transfer schematic diagram of Bi3+ to Mn4+. Table 1 Comparison of IQEs, excitation and emission wavelength of several Mn4+-activated far-red phosphors

Sample

Excitation peak

Main emission peak

IQE

Ref.

(nm)

(nm)

Sr9Y2W4O24:Mn4+

366

680

49.8%

[53]

KLaMgWO6:Mn4+

348

696

43%

[54]

Ca3La2W2O12:Mn4+

360

711

47.9%

[55]

CaYAlO4:Mg2+,Mn4+

348

710

48%

[56]

Ca14Ga10Zn6O35:Mn4+

350

705

50.9%

[42]

Ca3Al4ZnO10:Mg2+,Mn4+

358

714

60%

[57]

NaMgLaTeO6:Mn4+

365

703

57.43%

[58]

Sr3NaSbO6:Mn4+

317

695

56.2%

[59]

LaAlO3:Mg2+, Mn4+

340

729

78.6%

[47]

La1−xLuxAlO3:Mn4+

340

729

86%

[34]

LaAlO3:3%Ca2+,1.0%Bi3+,0.1%Mn4+

340

732

89.3%

This work

3.3 Zero thermal quenching behavior Luminescence stability of phosphors at the elevated temperatures is generally regarded as an essential criterion to evaluate their application potential [60]. For investigating the Ca2+, Bi3+ co-doping influence on thermal stability of LaAlO3:Mn4+, under 368 nm excitation, the temperature-dependent

normalized

integral

18

intensity

curves

of

LaAlO3:0.1%Mn4+,

LaAlO3:3%Ca2+,0.1%Mn4+ and LaAlO3:3%Ca2+,yBi3+,0.1%Mn4+ (y=0.6%, 0.8% and 1.0%) are presented in Fig. 5a. LaAlO3:0.1%Mn4+ shows a monotonic decreasing trend and remains 52% of its initial integral intensity at 150℃, while the Ca2+-doped sample exhibits a trend of increasing then decreasing and retains 72%. Furthermore, LaAlO3:3%Ca2+,yBi3+,0.1%Mn4+ (y=0.6%, 0.8% and 1.0%) phosphors also show the same trend like LaAlO3:3%Ca2+,0.1%Mn4+ samples, surprisingly, with the concentration of Bi3+ increasing from 0% to 1.0%, the final integral intensities are uplifted from 72% to 103%. It is worth noting that when the temperature is up to 150 ℃, LaAlO3:3%Ca2+,1%Bi3+,0.1%Mn4+ can still keep 103% of the initial integral intensity, namely zero-TQ. The common TQ process can be explained by the configurational coordinate diagram of Mn4+, as illustrated in Fig. 5b. The excited electrons transfer to the excited state 4T1 and 4T2 from 4A2 with increasing the temperature, and then the most excited electrons return to the ground state through the crossover point of 4T2 and 4A2 with non-radiative transition. In terms of PL relative intensity, typically, Fig. 5c presents the temperature-dependent PL spectra of LaAlO3:3%Ca2+,1%Bi3+,0.1%Mn4+. At the elevated temperature from 25-150℃, they show a red shift from 732 nm to 740 nm and broaden the peak shapes which can be explained by increasing the absorption of photons and improving the vibration transition coupling associated with the vibration modes of [MnO6] octahedron. Additionally, the relative intensities of these emissions display an obvious uplift even the temperature rises up to 125 ℃ and then descend but still have no obvious attenuation compared with initial intensity. When the temperature reaches to 150℃, the weak emission peak at 701 nm disappears maybe due to the following reasons: (i) as previous reports [34,47], the emission peak of 701 nm is designated as anti-Stokes sidebands and its intensity is affected by phonons, but the peak of 732 nm is Stokes sidebands dominated by

19

electrons. The high temperature simultaneously accelerates the energy loss of anti-Stokes and Stokes emission by the non-radiative transition and greatly decreases the intensity of this weak peak [47]. Dissimilarly, the intensity of 732 nm peak can still keep a high level owing to the compensation of the electrons coming from the traps [14]; (ii) the fine details of the spectrum are missing due to the large spectrometer slit setting, resulting in the spectrometer cannot display the very weak peak [35]. The pseudocolor map derived from the PL spectra at the temperature range of 25-150℃ is shown in Fig. 5d and it can intuitively visualize the temperature-dependent PL intensity, which confirms the ultra-thermal stability. The reason for suppressing TQ process by Ca2+ is that the smaller Ca2+ substitutes the lager La3+ to shrink the structural parameters and strengthen the bonding networks and bond strength, which can substantially minimize the emission loss with the elevated temperature [34,61]. To estimate the values of structural rigidity before and after Ca2+ doped, the following equation is used, which has been reported to be proportional to the rigidity of the crystal [62,63]:  D ,i 

3h 2TN A Ai k BU iso,i

(14)

where Ai is the atomic weight of the atom, Uiso,i is the atomic average displacement parameter, and the  D,i is inversely proportional to the value of Uiso. The Uiso values of the Ca2+-free and 3% Ca2+ doped samples derived by Rietveld refinement decreases from 0.046 to 0.040, demonstrating the increase of structure rigidity. However, the influence mechanism of Bi3+ on TQ process is not clear. To detailedly explain the zero-TQ mechanism by inducing by Ca2+ and Bi3+, TL spectra of LaAlO3:0.1%Mn4+, LaAlO3:3%Ca2+,0.1%Mn4+ and LaAlO3:3%Ca2+,1%Bi3+,0.1%Mn4+ are detected and presented in Fig. 5e. TL glow curves are recorded in range from 0 to 340 ℃ and two similar emission peaks 20

are observed at 31 ℃ and 123 ℃ or 125 ℃, implying the presence of two dominant trapping centers in the above mentioned phosphors. Additionally, it seems that Ca2+ affects trap B, but Bi3+ affects trap A, that's because trap B is an shallow trap which can be easily created by the impurity, but trap A is a deep trap and hard to be affected. However, the introduction of Bi3+ provides an opportunity for trap A to capture more electrons, thus affects the TL intensity of trap A. Studying the shape and location of these different peaks can provide the information about depths and distributions of the traps which reveal the energy compensation ability for TQ. Due to the peaks of traps B locates near room temperature, they have no influences in TQ process, so traps A plays a decisive role in zero-TQ phenomenon. Apparently, when Ca2+ ions were added into LaAlO3:0.1%Mn4+ lattice, the main TL peaks shift from 123 ℃ to 125 ℃ and show a little broader shape. On the other side, when to the more Bi3+ ions are doped into LaAlO3:3%Ca2+,0.1%Mn4+ lattice, the distinct TL intensity increase and wider shape are observed, demonstrating Bi3+ has the more stronger effect on the thermal stability improvement of Mn4+ emission than Ca2+ which is consistent with the results of the integral intensity. In order to further estimate the trap depths (EtrapA) and trap densities (N0), the calculation are performed by using the following equations [64,65]: E trapA  Tmax / 500

(15)

  N 0    I m /   2.52  10.2    g  0.42       

(16)

Where EtrapA is the thermo-active energy of trap depths (eV) denoting the energy gap between the trap levels and the conduction band of the host, and Tmax is the temperature (K) for which the TL peak is the maximum. β is the heating rate, ω, the FWHM, is known as the shape parameter and defined as ω=τ+δ, τ is the low-temperature half-width, δ is the high temperature half-width, the

21

asymmetry parameter μg=δ/(τ+δ), and Im is the intensity of the TL peak. The values of EtrapA and N0 of these three samples are calculated to be 0.79 eV, 0.80 eV, 0.80 eV and 1.0×105, 3.3×105, 7.8×105, respectively, indicating that Ca2+, Bi3+-doping can increase the trap depth and trap density which contain the more excited electrons to compensate the energy losses at the elevated temperature but it cannot totally explain the distinct improvement of TL intensity by Bi3+ doping. Thus another mechanism to contribute the compensation of TQ is proposed, the introduction of Bi3+ greatly increases trap density which creates more possibilities to capture and store more electrons during the energy transfer and release them to the compensate energy losses in TQ process. In conclusion, both Ca2+ and Bi3+ can restrain TQ of LaAlO3:Mn4+, but Bi3+ plays a major role in this process. To intuitively reflect the above energy compensation mechanism, a schematic diagram of zero-TQ is drawn in Fig. 5f. Taking LaAlO3:3%Ca2+,1%Bi3+,0.1%Mn4+ for example, when excited by UV light, the electrons arrive at 2E and 3P1 energy level of Mn4+ and Bi3+, meanwhile the energy transfer is produced then a part of electrons return to the 4A2g level with the far-red emission at 732 nm, the other part of electrons transfer to traps B through the path ① then deliver and store in traps A through the path ③. Attentionally, when the energy transfer from Bi3+ to Mn4+ (path ④), some of the transferring electrons can be captured by traps A and lie in them via path ⑤. This is the common emission and energy transfer process at room temperature. With the increase of temperature, under the effect of the thermal stimulation, the “stored” electrons in the traps A can be stimulated to the excited level through path ⑥ and finally return to ground state level. The higher the temperature rises to, the more electrons will be captured and stimulated to the excited level through path ⑥ until the traps A are empty. At the same time, it should be noted that the higher temperature will cause the enhanced non-radiative transition (Fig. 5b path

22

①), so the TQ behaviour should be the coupling contribution by the TQ effect and trap-electrons compensation effect. Less than 150 ℃, the electron population stimulated from path ⑥ is much more than that lost in non-radiative transition, leading to the observed increased emission intensity and

the

zero-TQ

behaviour.

The

decay

lifetimes

of

Mn4+

emission

in

LaAlO3:3%Ca2+,1%Bi3+,0.1%Mn4+ at various temperature are measured, as depicted in Fig. 5g, indicating the decay time of this sample increases gradually from 3.65 ms at 25 ℃ to 4.08 ms at 75 ℃, then decreases to 3.63 ms with further temperature elevating to 150 ℃ (Fig. 5h). It suggests that the extra energy transfer from the trap levels to the excited state of Mn4+ with the help of thermal energy. We noticed that the decay time decreases above 75 ℃, but the zero-TQ of photoluminescence is still observed. It implies that the thermal disturbance accelerates the capture and release of the excited electrons of traps, which exceeds the TQ process. 124%

150C

100C 103%

1.0

91% 80%

4+

0.8

LaAlO3:0.1% Mn 2+

72%

4+

LaAlO3:3% Ca ,0.1% Mn 2+

3+

4+

2+

3+

4+

2+

3+

4+

LaAlO3:3% Ca ,0.6% Bi ,0.1% Mn

0.6

LaAlO3:3% Ca ,0.8% Bi ,0.1% Mn

52%

LaAlO3:3% Ca ,1.0% Bi ,0.1% Mn

20

40

60

80 100 120 Temperature(C)

140

160

(c) LaAlO3:3%Ca2+,1%Bi3+,0.1%Mn4+ Relative intensity(a.u.)

Normalized Integral intensity(a.u.)

(a) 1.2

25C 50C 75C 100C 125C 150C

732 nm

690

700

710

720 730 Wavelength(nm)

740 nm

740

750

23

(e)

4+

LaAlO3:0.1% Mn

4+

2+

LaAlO3:3%Ca ,0.1% Mn

4+

3+

2+

Trap A 125°C 125°C 123°C

125 225 Temperature(C)

25

(g)

75

125 175 225 Temperature(C) 2+

3+

275

325

325

(h)

4+

LaAlO3:3%Ca ,1%Bi ,0.1%Mn

Logarithmic intensity(a.u.)

25C 50C 75C 100C 125C 150C

=3.65 ms =3.92 ms =4.08 ms =3.85 ms =3.72 ms =3.63 ms

ex=368 nm em=732 nm

4.0 Lifetime(ms)

Trap B

Normalized TL intensity(a.u.)

TL intensity(a.u.)

LaAlO3:3%Ca ,1% Bi ,0.1% Mn

3.8

3.6 0

2

4

6

Decay time(ms)

8

10

25

50

75 100 Temperature(C)

125

150

Fig. 5. (a) Temperature-dependent integrated emission intensity of LaAlO3:0.1%Mn4+, LaAlO3:3%Ca2+,0.1%Mn4+ and LaAlO3:3%Ca2+,yBi3+,0.1%Mn4+ (y=0.6%, 0.8% and 1.0%) under 368 nm excitation. (b) The configurational coordinate diagram of Mn4+. (c) Temperature-dependent PL spectra of LaAlO3:3%Ca2+,1%Bi3+,0.1%Mn4+ under 368 nm excitation. (d) The pseudocolor map derived from PL spectra of LaAlO3:3%Ca2+,1%Bi3+,0.1%Mn4+ in the range of 25-150 ℃. (e) Thermo-luminescence curves of LaAlO3:0.1%Mn4+, LaAlO3:3%Ca2+,0.1%Mn4+ and LaAlO3:3%Ca2+,1%Bi3+,0.1%Mn4+ in the range of 0-340 ℃. The inset is the normalized spectrum in the range of 75-340℃. (f) Schematic illustration of the mechanism for the thermal-enhanced luminescence in LaAlO3:3%Ca2+,1%Bi3+,0.1%Mn4+

phosphor.

(g)

Temperature-dependent

decay

curves

of

LaAlO3:3%Ca2+,1%Bi3+,0.1%Mn4+. (h) The changing trend of temperature-dependent decay lifetimes in LaAlO3:3%Ca2+,1%Bi3+,0.1%Mn4+.

24

3.4 Application for plant lighting Phytochrome is the most important photosynthetic pigment which is the photoreceptor for the reversible conversion under the red (PR, 660 nm) and far red (PFR, 730 nm) light. As shown in Fig. 6a, they affect the morphogenesis of plants throughout their life, from the seed germination to flowering, fruiting and aging. The control of plant growth by phytochromes mainly depends on the ratio of PFR/PR, so we can control the PFR/PR value through the far-red irradiation of ~730 nm and command the growth cycle of plants more accurately. Therefore, the ideal far-red phosphor should not only match the PFR spectrum but also less overlap with the PR spectrum. As mentioned above, LaAlO3:3%Ca2+,1%Bi3+,0.1%Mn4+ has a strong emission at 732 nm which perfectly suits the absorption spectrum of PFR. To quantificationally calculate the overlapping area with PR, we introduce the following equation [66]: SRPR 

 P d  100%  PR  d

(17)

Where SRPR is the spectrum resemblance of PR and PR(λ) which is the power distribution of the absorption spectrum and λ is the wavelength, while P   Pl   if PR  ＞Pl  

(18)

P   PR   if PR    Pl  

(19)

where Pl(λ) is the entire power spectrum of the given light source, and α is an arbitrary normalization constant, defined as the following:



 PR  d  Pl d

(20)

So according to the above equation, the value of SRPR is calculated to be 14% which shows a small overlap (Fig. 6b). In addition, the fabricated pc-LED shows a bright far red light, as shown in the inset of Fig. 6b. The luminous efficacy and CIE coordinates are 0.15 lm/W and (0.7316,

25

0.2659), respectively. The low luminous efficacy can be attributed to the fact that LaAlO3:3%Ca2+,1%Bi3+,0.1%Mn4+ phosphor exhibits emission in far red spectral region, where the human eye sensitivity is low [67]. However, the plants are sensitive to the far red light. In summary, LaAlO3:3%Ca2+,1%Bi3+,0.1%Mn4+ can be thought of a perfect candidate phosphor for accurately controlling the growth cycle of plants.

Fig. 6. (a) The mutual transformation and functional schematic diagram of PFR and PR. (b) The schematic diagrams of spectrum resemblance to PR.

4. Conclusion Remarkable zero-TQ of Mn4+ emission is first revealed in the perovskite phosphors meanwhile the high luminescence performance have been achieved in Ca2+, Bi3+ and Mn4+ co-doped LaAlO3 phosphors. The diversiform characterization techniques were utilized to

26

illuminate the mechanism of these phenomena. On the one hand, the introduction of Ca2+ can compensate the charge imbalance caused by Mn4+-doping and optimize the crystal field surrounding Mn4+ luminescence center, meanwhile these doping Ca2+ ions disorder the lattice to form the defect levels as the electron-trapping centers favouring the electrons transfer from the traps containing electron-hole pairs to the Mn4+. On the other hand, Bi3+ can not only efficiently transfer energy to Mn4+ to increase its emission at room temperature, but also offset the energy losses at the elevated temperature. Combining the positive effect of Ca2+ and Bi3+, LaAlO3:3%Ca2+,1%Bi3+,0.1%Mn4+ brings out the ideal luminescence performance and ultra-thermal stability. This strategy opens a new gateway for improving luminescence properties and developing thermally stability in Mn4+-activated oxide phosphors. Finally, the characteristic far-red-emitting of LaAlO3:3%Ca2+,1%Bi3+,0.1%Mn4+ phosphor shows a good application prospect for the plant seed germination, flowering, fruiting and aging.

Acknowledgments This work was supported by the Basic and Frontier Research Program of Chongqing Municipality (cstc2018jcyjAX0339, cstc2017jcyjBX0051), the Science and Technology Research Program of Chongqing Municipal Education Commission (KJZD-M201901301) and the Natural Science Foundation of Chongqing (cstc2019jcyj-msxm2493). The first author Shuangqiang Fang would like to thank his wife Mrs Xiaorui Peng for her support and love.

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(2018) 493-500. [2] P. Pust, P.J. Schmidt, W. Schnick, A revolution in lighting, Nat. Mater 14 (2015) 454-458. [3] S. Adachi, Photoluminescence spectra and modeling analyses of Mn4+-activated fluoride phosphors: A review, J. Lumin 197 (2018) 119-130. [4] M.G. Brik, A.M. Srivastav, On the optical properties of the Mn4+ ion in solids, J. Lumin 133 (2013) 69-72. [5] J.M. Xiang, J.Y. Chen, N.M. Zhang, H.B. Yao, C.F. Guo, Far red and near infrared double-wavelength emitting phosphor Gd2ZnTiO6: Mn4+, Yb3+ for plant cultivation LEDs, Dyes. Pigments 154 (2018) 257-262. [6] G.B. Loutts, M. Warren, L. Taylor, R.R. Rakhimov, H.R. Ries, G. Miller, M.A. Noginov, M. Curley, N. Noginova, N. Kukhtarev, H.J. Caulfield, P. Venkateswarlu, Manganese-doped yttrium orthoaluminate: A potential material for holographic recording and data storage, Phys. Rev. B 57 (1998) 3706. [7] Y. Zhydachevskii, D. Galanciak, S. Kobyakov, M. Berkowski, A. Kaminska, A. Suchocki, Y. Zakharko, A. Durygin, Photoluminescence studies of Mn4+ ions in YAlO3 crystals at ambient and high pressure, J. Phys.: Condens. Matter 18 (2006) 11385. [8] Y. Zhydachevskii, A. Durygin, A. Suchocki, A. Matkovskii, D. Sugak, P. Bilski, S. Warchol, Mn-doped YAlO3 crystal: a new potential TLD phosphor, Nucl. Instrum. Methods B 227 (2005) 545. [9] M.H. Du, Chemical trends of Mn4+ emission in solides, J. Mater. Chem. C 2 (2014) 2475-2481. [10] Z. Zhou, N. Zhou, M. Xia, M. Yokoyamab, H. T. (Bert) Hintzen, Research progress and application prospect of transition metal Mn4+-activated luminescent materials, J. Mater. Chem. C 4 (2016) 9143-9161.

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Highlights First obtain zero-thermal-quenching Mn4+-activated phosphor in perovskite structure. A high efficiency (IQE:89.3%) far-red-emitting phosphor is synthesized. Quantificationally evaluate the spectrum resemblance between obtained phosphor and phytochrome. Show a very good application prospect for improving plant photosynthesis.

Declaration of Interest Statement We declare that we do not have any commercial or associative interest that represents a conflict of interest in connection with the work submitted.

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