Structure, luminescence properties and energy transfer of terbium and samarium co-doped barium based apatite phosphor with tunable emission colour

Abstract

Ba₂La_2.85-xTb_0.15Sm_x(SiO₄)₃F (BLSOF:0.15Tb³⁺,xSm³⁺) is a polychromatic phosphor with an apatite structure that was manufactured through a solid-state process. X-ray diffraction (XRD) and a scanning electron microscope (SEM) were utilized to examine the phosphor's phase and morphology. Using the Rietveld technique, the as-prepared phosphor structure was validated. By progressively raising the doping contents of the samarium, the phosphors emitted multicoloured luminescence from short to long wavelengths as indicated by analysis of the optical performance. Overall, the data provide strong evidence that the transfer of energy in BLSOF:0.15Tb³⁺,xSm³⁺ is responsible for the phosphor's colour-tunable property.

Graphical abstract

The left graph shows the photoluminescence spectra of the Ba₂La₃(SiO₄)₃F:0.15Tb³⁺,xSm³⁺ phosphors, in which the energy transfer behavior occurs from Tb³⁺to Sm³⁺. And this results in these phosphors could emit typical multicolor light such as green, yellow, and reddish color with increasing doping contents of samarium as shown in the right graph.

Highlights

• •Ba₂La_2.85-x(SiO₄)₃F:0.15Tb³⁺,xSm³⁺ phosphors were prepared for the first time.
• •Energy transfer mechanism from Tb³⁺ to Sm³⁺ is quadrupole-quadrupole interaction.
• •The color of phosphors could be adjusted from green, yellow to reddish colour.

Rare earth; Photoluminescence; High-temperature solid-state method; Rare earth doped phosphor; Luminescence property.

1. Introduction

Due to their extraordinary and distinctive properties, light-emitting diodes (LEDs) are often regarded as representing the fourth generation of lighting sources in the general lighting market [1, 2, 3]. Attractive colours, tiny size, and exquisite construction all contribute to LEDs' popularity for use in decorating and illuminating urban areas [4, 5, 6]. One strategy for enabling LEDs to produce practical colours in their illuminance was to combine phosphors with n-UV chips, which emit light in the range of 350–420 nm [7, 8, 9]. To clarify more specifically, the phosphor consists of activators and hosts (there are a few cases in which sensitizers are incorporated) [10]. Recently, single-phase multicolour phosphors have preferentially recorded great improvement owing to the revelation that they can avoid various lighting limitations, including varying light decay durations and other issues. The ion pairs Tb³⁺→Sm³⁺ can create a light of multiple colours, which would be beneficial to meet our requirements. When used in phosphor activation processes, samarium is capable of producing red light, in contrast, terbium may be employed as a phosphor sensitizer to produce green light [11, 12, 13]. Apatite compound is frequently selected as the host owing to its great chemical stability that is unaltered by the fluctuating crystal field environment. The structural component of apatite has the chemical formula M₁₀(XO₄)₆Y₂. Depending on its valence, M could be a monovalent cation like an alkali metal, a divalent cation like an alkaline earth metal, or a trivalent cation like a lanthanide element; X represents P, Si, Ge, S, etc; Y typically represents either halogen or oxygen, each of which performs the role of a channel anion [14, 15, 16]. Apatite compounds, such as Sr₉Gd(PO₄)₅(SiO₄)F₂ [17]_, Ba₂La₃(SiO₄)₃F [18], and Ba₂La₃(SiO₄)₃Cl [19], have been used in various research fields. Given that a range of single-phase multicolour phosphors could be produced by transferring energy among rare earth ions, structural control makes it possible to produce a large number of variations that can be derived from the crystalline structure of apatite, which may greatly expand the variety of light-emitting materials and offer new alternatives for the solid-state lighting sector. In our previous paper, we studied the luminous properties and energy transfer of Ba₂La_2.85-xTb_0.15Eu_x(SiO₄)₃F [18] and Sr₂La₃(SiO₄)₃F:Tb³⁺,Sm³⁺ [20]. Nevertheless, research on terbium and samarium-doped Ba₂La₃(SiO₄)₃F (BLSOF) is lacking, as far as we can tell.

To examine its structure and luminous features, particularly its energy transfer, we prepared the Tb³⁺→Sm³⁺ doped with Ba₂La₃(SiO₄)₃F phosphor, which exhibits an apatite structure. By steadily altering the doping concentration of rare earth ions while keeping the host compound undisturbed, green, yellow, and reddish tunable phosphors were created. Phosphors were also analyzed for their morphology and spectrum characteristics. A greater comprehension of this single phase and multicolour phosphor might help expand the solid-state lighting knowledge base, which has profound implications in theory and practice.

2. Experimental details

2.1. Samples synthesis

A standard solid-state method was used at high temperatures to synthesize BLSOF:0.15Tb³⁺,xSm³⁺ phosphors. Throughout the experiment, we did not use the reducing atmosphere. The necessary chemicals are as follows: analytical grade BaCO₃, SiO₂, NH₄HF₂, and remarkably pure La₂O₃ (99.99%), Tb₄O₇ (99.99%), and Sm₂O₃ (99.99%). The chemicals used in the experiment were purchased from Zhengzhou Feynman Biotechnology Co., Ltd (Zhengzhou, China, mall.shiyanjia.com). The chosen compounds were weighted corresponding to their stoichiometric ratio (0.0001 g accuracy). These chemicals had not been subjected to treatment in any way before or during the weighing process. Afterwards, these compounds were mixed and subjected to thorough grinding in a single mortar. Subsequently, a corundum crucible containing the homogenous mixture was put into a high-temperature tube furnace and heated for 5h at 1350 °C before being left to cool to room temperature (RT). In preparation for subsequent structural and spectral tests, the sintered block was powdered by grinding.

2.2. Measurement

2.2.1. Structure and morphology

The diffraction data were gathered utilizing a D8 high-resolution X-ray diffractometer operated on 40 kV and 30 mA Cu-K radiation (λ = 0.15406 nm, 2θ = 10°–80°, Bruker, Germany). Depending on the X-ray diffraction (XRD) results, the powder form crystalline configuration was refined via a step scan at a speed of 0.02°/step. Each step lasted for a total of 3 s, and a range of 5°–130° was scanned in 2θ. By employing Topas 3.0's refining procedure, the crystallographic information file (CIF) was obtained. A Hitachi scanning electron microscope (SEM), model number JSM-6701F, made in Japan, was utilized to investigate the microscopic characteristics.

2.2.2. Spectra

The luminescent spectrum was measured at RT with a Hitachi F-4700 fluorescence spectrophotometer. This device was fitted with a xenon light with a power output of 150 W and 400 V. The luminous sample was placed in the sample cell of the spectrometer, and then a specific excitation wavelength was designated to irradiate the sample, to obtain the photoluminescence emission (PL) spectrum of the sample. Similarly, the sample was placed in the sample cell of the spectrometer, and then a specific emission wavelength was designated to monitor the photoluminescence excitation (PLE) spectrum of the sample. The sample's fluorescent lifetime of the samples was determined with the assistance of the Edinburgh FLS1000 fluorescent spectrometer. On the device known as the UV-4600, the spectra of the diffuse reflection were examined., and the test errors were eliminated with the use of the reference provided by the BaSO₄ standard whiteboard.

3. Results and discussions

The XRD technique was applied to analyze the crystalline structure of the synthesized phosphor, and the results of the tests are presented in Figure 1(a). The figure typically comprised XRD spectra of BLSOF:0.15Tb³⁺, BLSOF:0.15Tb³⁺,xSm³⁺（x = 0.12, 0.18, 0.24, 0.30）, BLSOF:0.15Sm³⁺ phosphors and Ba₂La₃(SiO₄)₃F (BLSOF) standard card (ICSD No.170852) was chosen to serve as the reference. There were no impurity peaks, and the intensity, number, and placement of the diffraction peaks were consistent with the typical card diffraction pattern. This illustrates that purity was absent in successfully producing the phosphors with an apatite structure. When Sm³⁺ and Tb³⁺ were introduced into the lattice replacing La³⁺, it results in the formation of a single-phase solid solution compound.

Figure 1.

(a) BLSOF:Tb³⁺,Sm³⁺ samples' XRD patterns. For vivid comparison, the standard card for Ba₂La₃(SiO₄)₃F (ICSD No.170852) is shown at the bottom. (b) The BLSOF:yTb³⁺ phosphors' emission spectra. (c) Relationship between BLSOF:yTb³⁺ phosphor concentration and intensity.

Determining the optimum doping concentration of ion pairs for energy transfer is crucial for studying the impact of structural modulation of this process. According to the single variable method, the content of one doped rare earth ion needs to be fixed first, and the content of the other rare earth ions can change. In general, the content of the sensitizer can be fixed and the content of the activator can be changed during energy transfer. In the Tb³⁺- Sm³⁺ double-doped phosphor studied in this paper, Tb³⁺ is used as a sensitizer, and Sm³⁺ is used as an activator. Therefore, for this system, it is necessary to fix the doping concentration of Tb³⁺ and change the doping concentration of Sm³⁺. Therefore, to obtain a suitable Tb³⁺ doping concentration, we did a group of concentration intensity experiments on the BLSOF-doped Tb³⁺ phosphor. The relationship between rare earth doping concentration of BLSOF: yTb³⁺ phosphor and emission intensity of phosphor is depicted in Figure 1(b) and (c). Evidently, when the Tb³⁺ doping concentration is 0.15 mol, the luminous intensity reaches the maximum, and then the concentration quenching occurs, leading to the reduction of luminous intensity. In all subsequently co-doped phosphors, the concentration of Tb³⁺ could be fixed to 0.15 mol.

The Topas 3.0 tool was employed to optimize the phosphor structure to obtain crystallographic data. The Rietveld refinement-related preliminary data pertains to the BLSOF crystalline structure. A refinement was made to the Rietveld structure. Figure 2(a) provides a graphic representation of the findings that were generated. The computed strength is represented by solid lines in red, the measured strength is displayed by circles in blue, and the refined peak location of the Bragg diffraction is shown by short vertical lines in orange. A comparative analysis was done between the actual and estimated intensity, and the variation was displayed as a green solid line in the graph. Table 1 illustrates the outcomes of convergence that might be attained via refinement, together with lower R factors: R_exp = 4.519%, R_wp = 6.062%, R_p = 4.515%, χ² = 1.342. The parameters of the cell are as follows: a = b = 9.86354(36) Å, c = 7.36339(28) Å, and V = 620.402(51) ų. Table 2 contains the refined atomic coordinates that were obtained, and the BLSOF displays the isotropic temperature factors for each component atom.

Figure 2.

(a) Ba₂La₃(SiO₄)₃F's Rietveld refinement XRD patterns generated by the TOPAS 3.0 software where the sample was held at room temperature. (b) The diagrammatic representation of the structure of the BLSOF along the c-direction.

Table 1.

Data on the crystallography of BLSOF.

Formula	Ba2La3(SiO4)3F
Space group	P63/m
Symmetry	Hexagonal
a/b(Å)	9.86354(36)
c(Å)	7.36339(28)
a/b	90o
γ	120o
V(Å3)	620.402(51)
R-Bragg	1.68801641
Rexp(%)	4.519
Rwp(%)	6.062
Rp(%)	4.515
χ2	1.342

Table 2.

Atomic coordinates of BLSOF.

Atoms	Wyckoff	x	y	z	occ	beq
La2	6h	0.24004(26)	0.98731(37)	0.25	0.55	1
Ba2	6h	0.24004(26)	0.98731(37)	0.25	0.45	1
La1	4f	0.6666667	0.3333333	0.00011(79)	0.55	1
Ba1	4f	0.6666667	0.3333333	0.00011(79)	0.45	1
Si1	6h	0.40505(94)	0.36865(92)	0.25	1	1
O1	6h	0.5974	0.4496	0.25	1	1
O2	6h	0.3442	0.4996	0.25	1	1
O3	12i	0.356	0.2721	0.0751	1	1
F	2a	0	0	0.25	1	2.81

A schematic representation of the BLSOF structure along the c-direction is displayed in Figure 2(b). La and Ba atoms each occupy two non-equivalent crystal positions within this structure, i.e. Ba1/La1 sites are placed at the 4f position (C₃ point symmetry), whereas Ba2/La2 sites are situated at the 6h position (C_S symmetry), each with nine and seven coordination, respectively. Silicon oxygen tetrahedron and fluorine ion are also marked in Figure 2(b).

BLSOF: 0.15Tb³⁺,0.16Sm³⁺’s microcosmic state is depicted in Figure 3. The sample has an uneven and granular morphology when seen underneath a microscope, as portrayed in Figure 3(a). The energy distribution spectra peaks of Sm, Tb, F, O, Si, La, and Ba are shown by the EDS in Figure 3(b), which elaborate on the synthesis of the desired samples. Figure 3(c) provides a graphical depiction of element distribution, showing the microscopically even distribution of the synthetic sample.

Figure 3.

(a) EDS spectrum, (b) SEM image and (c) element mapping of BLSOF: 0.15Tb³⁺,0.16Sm³⁺.

Spectral analysis of the BLSOF phosphor's emission and excitation was performed. Afterwards, the BLSOF:0.15Tb³⁺ phosphors' PLE and PL spectra were recorded (Figure 4(a)). The normal excitation peaks of Tb³⁺ were seen in this PLE spectra approximately between 325 and 500 nm, whereas 377 nm was found to be the wavelength at which the emission peak had the highest strength value (⁷F₆→⁵D₃). When excited at a spectrum of 377 nm, the BLSOF: 0.15Tb³⁺ phosphor displayed a strong luminescence. The emission spectrum showed four primary emission peaks: 492 nm (⁵D₄→⁷F₆ transition), 547 nm (⁵D₄→⁷F₅ transition), 592 nm (⁵D₄→⁷F₄ transition), and 624 nm (⁵D₄→⁷F₃ transition), where 547 nm showed the strongest peak.

Figure 4.

(a) Photoluminescence emission spectrum (right) and photoluminescence excitation spectrum (left) of BLSOF:0.15Tb³⁺ (b) Photoluminescence emission spectrum (right) and photoluminescence excitation spectrum (left) of BLSOF:0.15Sm³⁺ (c) Photoluminescence excitation spectrum (left) and photoluminescence emission spectrum (right) of BLSOF:0.15Tb³⁺, 0.16Sm³⁺.

The outcomes of the research conducted on the excitation and emission wavelengths of the BLSOF:0.15Sm³⁺ phosphor are demonstrated in Figure 4(b). When triggered by a light with a wavelength of 405 nm, the BLSOF: 0.15Sm³⁺ phosphor exhibited a very strong luminosity. There were three main emission peaks shown in emission wavelength: 567, 603, and 651 nm with ⁴G_5/2→⁶H_J/2 (J = 5, 7, 9) transition. Figure 4(a) and 4(b) depict the overlap between the PLE (405 nm, 440 nm, and 474 nm) of Sm³⁺ and PL (492 nm) of Tb³⁺ are shown in slash, which could be explained theoretically as the transmission of energy from Tb³⁺ to Sm³⁺.

Figure 4(c) displays the PL and PLE spectra of BLSOF:0.15Tb³⁺, 0.16Sm³⁺ phosphor. Since the main focus of our study was to evaluate the transfer of energy from Tb³⁺ to Sm³⁺, the excitation light of Tb³⁺ was chosen to excite the phosphor. Figure 4(c) provides a pink representation of the PL spectrum obtained after phosphor activation at 377 nm. As expected, the wavelengths of samarium and the corresponding emissions of terbium were subjected to superposition. Both the distinctive emission peaks of Sm³⁺ (e.g. ⁴G_5/2-⁶H_7/2 at 603 nm) and those of Tb³⁺(e.g. ⁵D₄-⁷F₅ at 547 nm) were observed in the emission wavelengths excited at 377 nm, establishing a firm groundwork for subsequent research on the colour refinement of this specific series of phosphors. Figure S1 contains a representation of the energy levels along with all of the related transitions to fully comprehend the mechanism of luminescence and the transfer of energy in a visualized manner.

After obtaining the spectrum of diffuse reflection, more research into the BLSOF optical band gap was conducted, as can be seen in Figure 5. Because BLSOF has a weak reflectivity in the UV region with wavelengths between 220-400 nm, it is deduced that it has a high absorption level in this region. As a result, it is possible to employ it as a substrate for luminous material-related energy absorption. Estimates of the BLSOF band gap Eg may be made using formula 1 [21, 22, 23]:

$${\left[hv\mathrm{F}\left(R\right)\right]}^2=\mathrm{A}\left(hv-Eg\right)$$ (1)

Figure 5.

Diffuse reflection spectrum of BLSOF host and corresponding [F(R)hν] [2]-hν curve (inset) of as-obtained BLSOF sample.

In line with Kubelka Munk formula 2 [24, 25]:

$$\mathrm{F}\left(\mathrm{R}\right)=\frac{{\left(1-\mathrm{R}\right)}^2}{2\mathrm{R}}=\mathrm{K}/\mathrm{S}$$ (2)

Where R stands for reflectivity, K denotes absorption, and S is for the scattering coefficient (1 can be taken here). When [hνF(R)] [2] = 0, the band gap of BLSOF can be derived using a linear model, approximated to 4.106 eV as illustrated in Figure 5. The wide band gap of BLSOF belongs to a semiconductor, which can accommodate various ions and their different excited states, is attractive for doping rare earth luminous ions and can serve as an appropriate substrate for luminescent materials.

The PL spectra of the BLSOF:0.15Tb3+,xSm3+(x = 0, 0.12, 0.16, 0.18, 0.20, 0.22, 0.24, 0.28, 0.30, 0.34) phosphors were displayed in Figure 6, where the signature spectra of Tb3+ (at 547 nm) and Sm3+ (at 603 nm) were further investigated. The general shape of each emission spectrum is consistent, whereas the strength of the peak fluctuates in a predictable manner as the amount of doping with Sm3+ rises (Figure 6(a)). This fluctuation could be represented in Figure 6(b). Tb3+ to Sm3+ energy transfer may be responsible for the progressive decline in Tb3+ peak intensity. The initial rise in peak intensity of Sm3+ and the following weakening after reaching the highest point at 0.16 Sm3+ doping concentration, might be a result of the concentration quenching.

Figure 6.

(a) The PL spectra of the BLSOF:0.15Tb3+,xSm3+(x = 0, 0.12, 0.16, 0.18, 0.20, 0.22, 0.24, 0.28, 0.30, 0.34) phosphors (b) The PL intensities of 547 nm (Tb3+) and 603 nm (Sm3+) when excited by 377 nm with the increase of Sm3+ contents (x).

The Tb3+ emission lifetime of BLSOF: 0.15Tb3+,xSm3+, excited at 377 nm and observed at 547 nm, was studied to assess the mechanisms driving Tb3+→Sm3+ energy transfer (Figure 7(a)). The outcomes matched the estimates of formula 1 [20, 21]:

$$\mathrm{I}\left(\mathrm{t}\right)={{\mathrm{I}}_0+\mathrm{A}}_1\exp \left(-\mathrm{t}/{\tau }_1\right)+{\mathrm{A}}_2\exp \left(-\mathrm{t}/{\tau }_2\right)$$ (1)

herein, I signify the PL intensity at time t, I₀ symbolizes the intensity at the start of the experiment, A₁ and A₂ symbolize the constants, t represents the time, and τ₁ and τ₂ denote the decay time following the energy-mediated excitation of the phosphor.

Figure 7.

(a)The fluorescence decay spectrum of BLSOF:0.15Tb³⁺,xSm³⁺. The wavelength of 377 nm is used for excitation, while 547 nm is used for monitoring. (b) The energy transfer efficiency of the phosphor under different contents of Sm³⁺.

Formula 2 [22, 23] below provided the average lifetime:

$${\tau }^{\ast }=\left(A_1{\tau }_1^2+A_2{\tau }_2^2\right)/\left(A_1{\tau }_1+A_2{\tau }_2\right)$$ (2)

The lifetimes of BLSOF:0.15Tb³⁺,xSm³⁺ (x = 0, 0.12, 0.16, 0.18, 0.20, 0.22, 0.24, 0.28, 0.30, 0.34) are obtained using the above formula, as listed in the legend of Figure 7(a). Notably, the lifetime of Tb³⁺ is reduced in the presence of a greater concentration of Sm³⁺, which offered additional evidence that a transfer of energy had taken place in the BLSOF:0.15Tb³⁺,xSm³⁺ between the ions Tb³⁺ and Sm³⁺.

The energy transfer efficiency in the BLSOF:0.15Tb³⁺,xSm³⁺ could be computed as per formula 3 [24, 25]:

$$\eta =1-\left({\tau }_s/{\tau }_{s0}\right)$$ (3)

Herein, τ_s0 is the value that indicates the luminescence intensity of the sensitizer Tb³⁺ when there is no Sm³⁺ present, and τ_s represents the luminescence intensity of Tb³⁺ when exposed to Sm³⁺. η denotes the energy transfer efficiency in BLSOF:0.15Tb³⁺,xSm³⁺ calculated as a function of x, as portrayed in Figure 7(b).

Once the doping concentration of samarium in the BLSOF:0.15Tb³⁺,xSm³⁺ is gradually increased from 0.12, 0.16, 0.18, 0.20, 0.22, 0.28, 0.30–0.34 mol, the energy transfer efficiency is calculated to be 27.05%, 33.43%, 39.11%, 42.54%, 45.01%, 45.44%, 50.76%, and 60.00%, respectively (Figure 7(b)). Notably, raising the doping concentration of the samarium contributed to a greater energy transfer efficiency.

The non-radiative transfer of energy may occur as a result of either the exchange interplay or the electric dipole interplay between the activators and the sensitizers, or between the activators themselves. A wide variety of non-radiative transmissions of energy may be categorized via critical distance analysis. Formula 4 below can be used to calculate the critical distance Rc in compliance with the BLASSE theory [26, 27, 28]:

$$R_c\approx 2{\left(3V/4\pi x_{c}N\right)}^{1/3}$$ (4)

herein, the volume of a unit cell is symbolized by V, samarium and terbium's total concentration is denoted by the symbol x_c when the energy efficacy is set to 0.5, and the parameter of N indicates the number of cations present for a single unit cell. For Ba₂La₃(SiO₄)₃F host, N = 10 and V = 608.8 Å [3]. As displayed in Figure 7(b), when the energy transfer efficiency is at a value of 0.5, the Sm³⁺ doping concentration is approximately 0.3 mol. Therefore, x_c = 0.3 + 0.15 = 0.45 mol. According to the findings of the computation, the value of Rc for BLSOF:0.15Tb³⁺, xSm³⁺ is approximately 0.637032 nm. Since the critical distance for the BLSOF:0.15Tb³⁺, xSm³⁺ is >0.5 nm, electric dipole interactions serve as the mode of xSm³⁺ for transferring energy.

There are three distinct categories of interactions between electric dipoles: dipole-dipole, dipole-quadrupole, and quadrupole-quadrupole interactions. Applying formula 5 below further substantiates the mode of transferring energy [29, 30, 31, 32]:

$$\left(I_{s0}/I_s\right)\propto C^{n/3}$$ (5)

Herein, I_S0 symbolizes the PL intensity of Tb³⁺ in BLSOF:0.15Tb³⁺ phosphor; I_S highlights the PL intensity of Tb³⁺ in BLSOF:0.15Tb³⁺,xSm³⁺ phosphor; C represents the total concentration of terbium and samarium; n symbolizes the constant, which can be used to explain how samarium and terbium exchange energy with one another. The energy transfer occurs through dipole-dipole, dipole-quadrupole, and quadrupole-quadrupole interactions for n = 6, 8, and 10, correspondingly. Figure 8 demonstrates that the optimum linear fitting I_S0/I_S and C^n/3 (n = 6, 8, or 10) when n is 10, suggesting that the energy transfer mechanism underpinning BLSOF:0.15Tb³⁺,xSm³⁺ is the quadrupole-quadrupole interface.

Figure 8.

The relationship between I_S0/I_S of Tb³⁺ in BLSOF and C^6/3, C^8/3 and C^10/3.

Table 3 provides the outcomes of the analysis of the BLSOF:0.15Tb³⁺,xSm³⁺ phosphor's emission spectra, which helped determine its colour coordinates. These colour coordinates have been highlighted on the CIE diagram so that the phosphor colour alteration may be more prominent (Figure 9). Evidently, the modification of the ratio of Tb³⁺ to Sm³⁺ in the doping concentrations contributed to a shift in the phosphor colour from green (0.37, 0.61) to yellow and reddish colour (0.58, 0.42). The series of phosphors that are produced when they are exposed to irradiation from a 365 nm miner's lamp at samarium doping concentrations of 0, 0.12, and 0.20 mol of BLSOF:0.15Tb³⁺,xSm^3+, and BLSOF:0.15Sm³⁺, correspondingly, are shown in the images that are located from top to bottom in Figure 9. Overall, this set of new single-phase phosphors, known as BLSOF:0.15Tb³⁺, xSm [3], displays the significance of configurable polychromatic luminescence owing to energy transfer.

Table 3.

CIE coordinate values of BLSOF:0.15Tb³⁺, xSm³⁺ at different Sm³⁺ doping concentrations.

Formula	CIE Value
Ba2La2.85(SiO4)3F:0.15Tb3+	(0.3672,0.6111)
Ba2La2.73(SiO4)3F:0.15Tb3+, 0.12Sm3+	(0.4663,0.5185)
Ba2La2.69(SiO4)3F:0.15Tb3+, 0.16Sm3+	(0.4754,0.5115)
Ba2La2.67(SiO4)3F:0.15Tb3+, 0.18Sm3+	(0.4748,0.5105)
Ba2La2.65(SiO4)3F:0.15Tb3+, 0.20Sm3+	(0.4770,0.5072)
Ba2La2.63(SiO4)3F:0.15Tb3+, 0.22Sm3+	(0.4788,0.5051)
Ba2La2.61(SiO4)3F:0.15Tb3+, 0.24Sm3+	(0.4748,0.5065)
Ba2La2.57(SiO4)3F:0.15Sm3+, 0.28Sm3+	(0.4617,0.5142)
Ba2La2.55(SiO4)3F:0.15Tb3+, 0.30Sm3+	(0.4586,0.5171)
Ba2La2.51(SiO4)3F:0.15Tb3+, 0.34Sm3+	(0.4581,0.5174)
Ba2La2.85(SiO4)3F:0.15Sm3+	(0.5783,0.4168)

Figure 9.

CIE of BLSOF:0.15Tb³⁺, xSm³⁺ when excited by 377 nm.

4. Conclusions

Single-phase polychromatic phosphor BLSOF:0.15Tb³⁺,xSm³⁺ was synthesized using the commonly used high-temperature solid phase method. Extensive research has been conducted to investigate both the structure and the optical characteristics of this phosphor. We concluded based on our analysis that the optimum concentration of Sm³⁺ to employ in BLSOF:0.15Tb³⁺,xSm³⁺ is 0.16 mol. In BLSOF, it was discovered that the mode of energy transfer from Tb³⁺ to Sm³⁺ occurs via the quadrupole-quadrupole (q-q) interplay. Based on the amounts of Tb³⁺/Sm³⁺ that are doped into the phosphors, the colour of the phosphors may change from green to yellow to reddish colour. Overall, BLSOF:0.15Tb³⁺,xSm³⁺ may act as an excellent single-phase multicolour phosphor.

Declarations

Author contribution statement

Kun Nie: Conceived and designed the experiments; Wrote the paper.

Ranan Zhou: Performed the experiments.

Chi-An Cheng, Lefu Mei, Haikun Liu, Yuanyuan Zhang, Luoxin Wang, Hua Wang: Analyzed and interpreted the data.

Xiuqiang Duan, Ziyao Hu: Contributed reagents, materials, analysis tools or data.

Xiaoxue Ma: Conceived and designed the experiments; analyzed and interpreted the data.

Funding statement

Lefu Mei was supported by National Natural Science Foundation of China [51872269], National Natural Science Foundation of China [52274273].

Dr. Kun Nie was supported by the Science and Technology Research Project of Hubei Provincial Department of Education [B2021091], Key Laboratory for New Textile Materials and Applications of Hubei Province(Wuhan Textile University) [FZXCL202107], Key Laboratory of Testing and Tracing of Rare Earth Products for State Market Regulation (Jiangxi University of Science and Technology) [TTREP2022YB04].Haikun Liu was supported by Basic and Applied Basic Reuter Foundation of Guangdong Province [2021A1515110702].Yuanyuan Zhang was supported by Basic and Applied Basic Reuter Foundation of Guangdong Province [2021A1515110283], China Postdoctoral Science Foundation [2021M702562].

Data availability statement

Data will be made available on request.

Declaration of interests statement

The authors declare no conflict of interest.

Additional information

No additional information is available for this paper.

Appendix ASupplementary data

The following is the supplementary data related to this article:

Figure S1.