Ce3+/Mn2+-activated Ca7(PO4)2(SiO4)2: efficient luminescent materials for multifunctional applications

Jia Zhang; Lei Zhao; Xintian Bian; Guibin Chen

doi:10.1364/OE.26.00A904

1. Introduction

Since environmental protection and power saving have become global issues in recent years, phosphors conversion light-emitting diodes (LEDs) have been extensively investigated due to their long lifetime, energy saving qualities, high luminous efficiency, reliability and low maintenance [1–3]. At present, the LEDs can serve in many fields, such as solid lighting, backlights, traffic signals, and plants growth [4,5]. First, as one of the most important applications for solid lighting, white LEDs are commercially available by combining the blue LED chip with a yellow-emitting Y₃Al₅O₁₂:Ce³⁺ phosphor. Unfortunately, white light of this kind shows poor color rendering index (Ra < 80) and high correlated color temperature (CCT > 4500 K) owing to the red deficiency [6]. To overcome these disadvantages, an alternative strategy by combination of a near-ultraviolet (NUV) LED chip with tri-color phosphors (blue, green and red) has been developed [7]. As is known, the commercial blue-emitting BaMgAl₁₀O₁₇:Eu²⁺ (BAM) phosphor shows higher quantum efficiency (QE > 80%) [1] compared with the green and red phosphors, but the preparation temperature is high, ~1500 °C [8]. On the basis of the subject of power saving, it is necessary to develop new efficient blue-emitting phosphors owing to not only the further enhancement of luminous efficiency but also the decrease of the preparation temperature. Second, LED can be an artificial flexible lighting source for plant tissue culture. It is known that the energy for plants growth is mostly derived from light. However, the plants usually show selective light absorption. For instance, the carotenoids mainly absorbs purple blue light, but the chlorophyll absorbs not only the purple blue but also red light. On the other hand, the absorption spectra for different green plants are nearly the same. Thus, if tunable-emission of a luminescent material is available, different color blending schemes could cause various morphological, anatomical, and physiological attributes of plants growth in vitro [9]. Based on this point, exploring new emission-tunable phosphors is urgent currently in order to study the effect of LEDs on plants.

Nagelschmidtite Ca₇(PO₄)₂(SiO₄)₂ (CPS) with a phosphate-sillcate framework has been well-known as a natural mineral [10]. Due to the high chemical and physical stability and low cost synthesis for phosphate and sillcate, the CPS could be an excellent host material for phosphors. So far, the Eu²⁺-activated CPS has been reported by Wei and Shi [11,12]; the luminescence of Dy³⁺/Eu³⁺-doped CPS was studied by Li [13]. Besides the above used activator ions, the Ce³⁺ and Mn²⁺ are also two very commonly used luminescent ions. It is well known that the Ce³⁺ with 4f-5d transition is allowed and can result in strong excitation/absorption intensity [14]. However, the Mn²⁺ is difficult to be excited owing to the parity-forbidden transition, although it can demonstrate a broadband red emission from 500 to 700 nm [15]. Fortunately, it is possible to introduce sensitizers, such as Ce³⁺ and Eu²⁺, to enhance the Mn²⁺ emission, by which the tunable-emission can be also produced. Many Ce³⁺-Mn²⁺ codoped phosphors for achieving tunable emission have been reported, such as Ca_2.5Sr_0.5Al₂O₆:Ce³⁺,Mn²⁺, Ca₉Sc(PO₄)₇:Ce³⁺,Mn²⁺, CaZrSi₂O₇:Ce³⁺,Mn²⁺, Ba₉Lu₂Si₆O₂₄:Ce³⁺,Mn²⁺, and Y₁₀(Si₆O₂₂N₂)O₂:Ce³⁺,Mn²⁺ [14–18]. To the best of our knowledge, the photoluminescence of the Ce³⁺/Mn²⁺ activated CPS phosphors have not been investigated. In this work, to develop new efficient blue and emission-tunable luminescent materials for LEDs, the CPS:Ce³⁺,Li⁺, Mn²⁺ phosphors were designed by high-temperature solid-state reaction method, and their luminescence properties were evaluated.

2. Experimental

The Ca_7(1-2x)(PO₄)₂(SiO₄)₂:xCe³⁺,xLi⁺ (abbreviated as CPS:xCe³⁺,xLi⁺ 0.2% ≤ x ≤ 4%) and Ca_7(0.94-y)(PO₄)₂(SiO₄)₂:3%Ce³⁺,3%Li⁺,yMn²⁺ (abbreviated as CPS:3%Ce³⁺,3%Li⁺,yMn²⁺, 0.5% ≤ y ≤ 3%) samples were prepared by the solid-state reaction method. The raw materials were CaCO₃ (99%), (NH₄)₂HPO₄ (99%), SiO₂ (99%), Li₂CO₃ (99%), MnCO₃ (99%), and CeO₂ (99.99%). The equal amount of Li⁺ was used as charge compensation reagent when Ce³⁺ was doped. Stoichiometric amounts of the above reagents were ground together in an agate mortar, and then calcined at 1400 °C for 5 h in a reduction atmosphere (95%N₂-5%H₂).

The phase purity was determined by an ARL X'TRA powder X-ray diffractometer (XRD) with Cu Kα radiation (λ = 1.5418 Å) operating at 40 kV and 35 mA. The morphology was inspected by field emission scanning electron microscope (FESEM, FEI, Quanta FEG). The luminescence spectra were recorded on an EI-FS5 fluorescence spectrophotometer. The QE was determined by measuring the total absorption using an integrating sphere with the EI-FS5 spectrophotometer system. The decay curves and time-resolved photoluminescence (TRPL) spectra were recorded on the EI-FS5 fluorescence spectrophotometer with a 365 nm pulse source (the time range, channels and lamp trigger delay were set as 0.5 μs, 1000, and 0.03 μs, respectively). The temperature-dependent measurement was also carried out by using the EI-FS5 fluorescence spectrophotometer, during which the samples were mounted on a heating device and the temperature could change from room temperature to 573 K.

3. Results and discussion

Figure 1(a) shows the XRD patterns of the typical CPS:xCe³⁺,xLi⁺ (0.2% ≤ x ≤ 4%) and CPS:3%Ce³⁺,3%Li⁺,yMn²⁺ (y = 0.5% and 2%) phosphors. The diffraction peaks agree well with the JCPDS standard card (No. 11-0676), indicating the as-prepared samples are single-phase and the introduction of the dopants does not cause any impurity phase obviously. To learn the morphology characteristics of the phosphors, Fig. 1(b) presents the SEM image of the typical CPS:3%Ce³⁺,3%Li⁺ sample. It can be found that the particles’ scale is inhomogeneous ranging from 5 to 20 μm on the whole. But the sample demonstrates relatively good particle dispersion for the high-temperature solid-state reaction.

Fig. 1 XRD patterns of CPS:xCe³⁺,xLi⁺ (0.2% ≤ x ≤ 4%) and CPS:3%Ce³⁺,3%Li⁺,yMn²⁺ (0.5% ≤ y ≤ 3%).

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The excitation spectrum of the typical CPS:3%Ce³⁺,3%Li⁺ sample is shown in Fig. 2(a). An intense excitation band covering a broad range of 240-400 nm is found, which can well match with the NUV LED chip. This excitation band could be attributed to the 4f¹-4f⁰5d¹ transition of Ce³⁺ [19]. The emission spectra of the CPS:xCe³⁺,xLi⁺ (0.2% ≤ x ≤ 4%) phosphors upon 365 nm excitation are also presented in Fig. 2(a). Broad emission bands from 375 to 650 nm appear, which result from the 4f⁰5d¹-4f¹ transition of Ce³⁺. It can be also found that the emission position changes with the Ce³⁺ concentration. To understand this point, Fig. 2(b) shows the normalized emission spectra of the CPS:xCe³⁺,xLi⁺ (0.2% ≤ x ≤ 4%) phosphors. A continuous red-shift is found for these emission bands. According to Ref [20]. for Eu²⁺ ion, it has been introduced that energy can be transferred to Eu²⁺ ions emitting at lower energy though energy migration in the energy transfer (ET) process. Similarly, the case for Ce³⁺ in this work could be combined with the ET between different Ce³⁺ occupation sites. As mentioned in Ref [11], more than one Ca²⁺ site could exist in the CPS compound. So different Ce³⁺ emission centers could be generated when the Ce³⁺ is introduced into the host lattices randomly. To explain this point, the TRPL spectra of the CPS:3%Ce³⁺,3%Li⁺ sample were illustrated in Fig. 3(a). With prolonging decay time, the emission intensity decreases sharply. The changes of the position and shape of the Ce³⁺ emission bands with decay time can be seen in the normalized TRPL spectra in Fig. 3(b). It is obvious that a shift (for about 35 nm) of the emission band towards the long-wavelength direction appears with prolonging decay time. At the same time, the band-width is increased. The above observation mainly result from different Ce³⁺ emission centers with different decay rate in emission intensity. As a result, the energy can be transferred to Ce³⁺ emitting at lower energy possibly via multiple ET steps. The decreasing Ce³⁺ decay lifetime with increasing Ce³⁺ concentration also supports this conclusion, because there will be additional decay channels that shorten the lifetime of the excited state owing to this ET, especially on the shorter wavelength side of the emission band [20]. Figure 4 shows the decay curves of the CPS:xCe³⁺,xLi⁺ (0.2% ≤ x ≤ 4%) phosphors by exciting at 365 nm and monitoring 395 nm. These decay curves can be fitted via a double-exponential function as [21]

I = A_{1} \exp (- t / τ_{1}) + A_{2} \exp (- t / τ_{2})

where τ₁ and τ₂ are fast and slow components of the emission lifetimes, and A₁ and A₂ are fitting parameters, respectively. The corresponding τ_i and A_i (i = 1, 2) values were summarized in Table 1. By using the following equation [22]

< τ > = (A_{1} τ_{1}^{2} + A_{2} τ_{2}^{2}) / (A_{1} τ_{1} + A_{2} τ_{2})

the average lifetimes were calculated to be 40.5, 38.8, 37.5, 36.6, 35.1 and 34.5 ns for x = 0.2%, 0.5%, 1%, 2%, 3% and 4%, respectively. Hence, the Ce³⁺ lifetime exhibits a gradual decrease with increasing Ce³⁺ concentration. From Fig. 2(a), it can be also found that the optimal Ce³⁺-doping concentration is for 3%. The emission intensity starts to decrease beyond this concentration due to the concentration quenching, for which the excited energy could migrate among the neighbouring Ce³⁺ ions by resonant ET until the energy reaches the defects where it can lose in some way [23]. To understand this ET mechanism, it is necessary to obtain the critical distance (Rc) for ET between two activator ions at the quenching concentration. Here, the Dexter formula is employed, expressed as follows [24]:

R_{c}^{6} = 0.63 \times 10^{28} \times \frac{Q_{A}}{E^{4}} \int F_{s} (E) F_{A} (E) d E

where Q_A = 4.8 × 10⁻¹⁶f_d is the absorption cross section of Eu²⁺, f_d ≈0.01 is the electric-dipole oscillator strength for Ce³⁺, ∫F_s(E)F_A(E)dE represents the spectral overlap between the normalized shapes of Ce³⁺ emission F_s(E) and excitation F_A(E), and E (in electronvolts) is the energy of maximum spectral overlap. In the CPS:3%Ce³⁺,3%Li⁺, the spectral overlap and the E value were calculated to be 0.0267 eV⁻¹ and 3.22 eV, respectively. Hence, the R_c was obtained to be 14.0 Å. The critical distance is similar to those of some other Ce³⁺-activated phosphors, such as CaSrSiO₄:Ce³⁺ (R_c = 12.05 Å) and Sr_2.975-xBa_xCe_0.025AlO₄F (R_c = 16 Å) [25,26].

Fig. 2 (a) Excitation spectrum of CPS:3%Ce³⁺,3%Li⁺ and emission spectra of CPS:xCe³⁺,xLi⁺ (0.2 ≤ x ≤ 4%); (b) normalized emission spectra of CPS:xCe³⁺,xLi⁺ (0.2 ≤ x ≤ 4%).

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Fig. 3 (a) TRPL spectra of CPS:3%Ce³⁺,3%Li⁺; (b) normalized TRPL spectra of CPS:3%Ce³⁺,3%Li⁺.

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Fig. 4 Decay curves of CPS:xCe³⁺,xLi⁺ (0.2 ≤ x ≤ 4%).

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Table 1. τ_i and A_i (i = 1, 2) values of CPS:xCe³⁺,xLi⁺ (0.2% ≤ x ≤ 4%) by exciting at 365 nm and monitoring 395 nm

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To evaluate the brightness of the present phosphor, Fig. 5 shows the emission spectra of the CPS:3%Ce³⁺,3%Li⁺ and commercial BAM phosphors under 365 nm excitation. The predominant emission intensity of the CPS:3%Ce³⁺,3%Li⁺ is about half of that of the BAM, but the CPS:3%Ce³⁺,3%Li⁺ possesses a larger full width at half maximum (FWHM) relative to the BAM. As a result, the integrated intensity of the CPS:3%Ce³⁺,3%Li⁺ phosphor is about 101.2% as strong as that of the commercial BAM phosphor. The QEs for the CPS:3%Ce³⁺,3%Li⁺ and BAM phosphors were measured to be 90.4% and 86.5%, respectively. So, the CPS:3%Ce³⁺,3%Li⁺ phosphor has a higher luminous efficiency relative to the BAM. Moreover, the larger FWHM for the CPS:3%Ce³⁺,3%Li⁺ could generate white light with excellent Ra value by combining other phosphors in a fabrication of LEDs [6].

Fig. 5 Comparison of emission spectra of CPS:3%Ce³⁺,3%Li⁺ and BAM.

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To evaluate the thermal stability of the CPS:3%Ce³⁺,3%Li⁺ phosphor, Fig. 6(a) represents its emission spectra by exciting at 365 nm under various temperatures. It is obvious that the emission intensity decreases gradually with increasing temperature. From the dependence of the emission intensity on temperature in Fig. 6(b), it can be seen that the emission intensity at 423 K is decreased by 30% of the initial value, and thermal quenching temperature T_0.5 (the temperature at which the emission intensity is half of its initial intensity) is about 473 K. Although the thermal stability of CPS:3%Ce³⁺,3%Li⁺ is inferior to that of BAM, it has a relatively good temperature quenching effect, which reveals a better or comparable thermal stability compared with many other blue phosphors with high luminous efficiency reported previously, such as BaZrSi₃O₉:Eu²⁺ [27], Ba₂Ln(BO₃)₂Cl:Ce³⁺ (Ln = Gd, Y) [28], and Ca_5.45Li_3.55(SiO₄)₃O_0.45F_1.55:Ce³⁺ [29]. Also, the CPS:3%Ce³⁺,3%Li⁺ phosphor can exhibits a higher T_0.5 value than some other silicophosphate-based phosphors such as Ca₅Y₃Na₂(PO₄)₅(SiO₄)F₂:Eu (T_0.5 = 383 K) and Sr₃CeNa(PO₄)₂SiO₄:Eu (T_0.5 = 423 K) phosphors [1,30]. According to Ref [31], the activation energy can be calculated by the Arrhenius equation:

I (T) = \frac{I_{0}}{1 + A \cdot \exp (- \frac{Δ E}{k T})}

where I₀ is the initial emission intensity, I(T) is the intensity at different temperatures, ΔE is activation energy of thermal quenching, A is a constant for a certain host, and k is the Boltzmann constant (8.629 × 10⁻⁵ eV/K). The plot of ln[(I₀/I) - 1] vs. 1/kT for CPS:3%Ce³⁺,3%Li⁺ is shown in Fig. 6(c), from which a linear relationship

\ln [(I_{0} / I) - 1] = 7.04 - 0.286 T

has been obtained. Hence, the ΔE equals to 0.286 eV, which is higher than those of some other Ce³⁺ activated phosphors such as BaY₂Si₃O₁₀:Ce³⁺ (ΔE = 0.25 eV) and Y₄Si₂O₇N₂:Ce³⁺ (ΔE = 0.22 eV) [31,32].

Fig. 6 (a) Emission spectra of CPS:3%Ce³⁺,3%Li⁺ measured under various temperatures; (b) relative emission intensity of CPS:xCe³⁺,xLi⁺ as a function of temperature; (c) plot of ln[(I₀/I) - 1] vs. 1/kT for CPS:xCe³⁺,xLi⁺.

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To supply the red emission component in the spectra, a series of Ce³⁺-Mn²⁺ codoped CPS phosphors were designed. Figure 7(a) depicts the emission spectra of the CPS:3%Ce³⁺,3%Li⁺,yMn²⁺ (0 ≤ y ≤ 3%) samples under 365 nm excitation. When the Mn²⁺ is incorporated, a new emission band around 650 nm comes out, which can be ascribed to the ⁴T₁-⁶A₁ transition of Mn²⁺ [33]. With increasing Mn²⁺ concentration, the emission intensity of Ce³⁺ decreases gradually and the Mn²⁺ emission has been enhanced until y = 2%. This observation reveals that an ET from Ce³⁺ to Mn²⁺ may occur. To interpret this point, the decay curves of the CPS:3%Ce³⁺,3%Li⁺,yMn²⁺ (0 ≤ y ≤ 3%) phosphors with 365 nm excitation and 439 nm emission are depicted in Fig. 7(b), which can be well fitted by Eq. (1). The corresponding τ_i and A_i (i = 1, 2) values are shown in Table 2. Using Eq. (2), the average lifetimes of CPS:3%Ce³⁺,3%Li⁺,yMn²⁺ have been determined to be 50.4, 48.5, 47.3, 44.8 and 42.1 ns for y = 0, 0.5%, 1%, 2%, and 3%, respectively. The decreasing average lifetime mainly results from the ET from Ce³⁺ to Mn²⁺. To learn the change of the emitting-light-color by codoping Mn²⁺ of different concentrations, the Commission International del’Eclairage (CIE) chromaticity coordinates of the CPS:3%Ce³⁺,3%Li⁺,yMn²⁺ (0 ≤ y ≤ 3%) phosphors were calculated, as shown in Fig. 8. It can be noticed that the emission color of the phosphors can be tuned from blue towards pink region gradually with increasing Mn²⁺ dopant content, which is in accordance with the ET process of the emission spectra in Fig. 7(a). In order to investigate the ET mechanism, the following relation can be employed on the basis of Dexter’s ET expression of multipolar interaction and Reisfeld’s approximation [34,35]:

\frac{τ_{S 0}}{τ_{S}} \propto C^{α / 3}

where C is the concentration of Mn²⁺, τ_S and τ_S0 are the lifetime of the sensitizer Ce³⁺ in the present and absence of Mn²⁺, respectively. (τ_S0/τ_S) ∝ C with α = 6, 8 and 10 corresponds to the dipole-dipole, dipole-quadrupole, and quadrupole-quadrupole interactions, respectively. The dependences of τ_S0/τ_S of Ce³⁺ on C_Mn^6/3, C_Mn^8/3, and C_Mn^10/3 are demonstrated in Fig. 9(a)-9(c), respectively. It can be noticed that the linear relationship can be obtained only for α = 6, which indicates that the ET from Ce³⁺ to Mn²⁺ takes place via a dipole-dipole mechanism.

Fig. 7 (a) Emission spectra of CPS:3%Ce³⁺,3%Li⁺,yMn²⁺ (0 ≤ y ≤ 3%) under 365 nm excitation; (b) decay curves of CPS:3%Ce³⁺,3%Li⁺,yMn²⁺ (0 ≤ y ≤ 3%).

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Table 2. τ_i and A_i (i = 1, 2) values of CPS:3%Ce³⁺,3%Li⁺,yMn²⁺ (0 ≤ y ≤ 3%) by exciting at 365 nm and monitoring 439 nm

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Fig. 8 CIE chromaticity diagram for CPS:3%Ce³⁺,3%Li⁺,yMn²⁺ (Points 1-5 are for y = 0, 0.5%, 1%, 2%, and 3%, respectively).

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Fig. 9 Dependence of τ_S0/τ_S of Ce³⁺ on (a) C_Mn^6/3, (b) C_Mn^8/3 and (c) C_Mn^10/3.

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Figure 10(a) shows the absorption spectra for chlorophyll a, chlorophyll b, and carotenoids in plants. For chlorophyll a, the absorption bands are mainly located in the purple blue and red ranges. For chlorophyll b, the absorption bands mostly exist in the cyan and red regions. However, the absorption bands of carotenoids just lie in the range from purple and cyan. Thus, for the plants growth application, it is necessary to obtain broad emission bands in the above regions for phosphors in LEDs. Figure 10(b) and 10(c) present the emission spectra upon 365 nm excitation of the CPS:3%Ce³⁺,3%Li⁺,yMn²⁺ phosphors for y = 0.2 and 0, respectively. It can be noticed that the strong emission of Ce³⁺ in the broad wavelength range from 375 to 575 nm can cover all the absorption bands of chlorophyll a, chlorophyll b, and carotenoids from 390 to 525 nm. On the other hand, the red Mn²⁺ emission in the region of 600-725 nm can give the supplement for the absorption in the red range for chlorophyll a and b. Thus, the CPS:3%Ce³⁺,3%Li⁺,yMn²⁺ phosphors could be promising in the plants growth.

Fig. 10 (a) Absorption spectra of plants; emission spectra of CPS:3%Ce³⁺,3%Li⁺,yMn²⁺ ((b) and (c) are for y = 0.2 and 0, respectively).

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Figure 11 presents the electroluminescence (EL) spectra of phosphor converted (pc)-LED lamps. The fabrication was carried out with 365 nm LED chip and different kinds of phosphors and driven with 350 mA current. For the combination of the CPS:3%Ce³⁺,3%Li⁺ phosphor with the 365nm chip, an intense blue emission has been obtained (see insets (A) and (B)). The CIE chromaticity coordinates were obtained to be (0.202, 0.214). When the 365 nm chip is fabricated with the tri-color CPS:3%Ce³⁺,3%Li⁺, commercial (Ba,Sr)₂SiO₄:Eu²⁺ and CaAlSiN₃:Eu²⁺, a warm white light can be produced (see insets (C) and (D)). The corresponding CIE chromaticity coordinates and CCT were calculated to be (0.361, 0.401) and 3683 K, respectively. The obtained 14 CRIs are shown in Table 3, where the average value Ra was calculated to be 92.5. Hence, high color rendering index has been achieved in this work.

Fig. 11 EL spectra of pc-LED lamps fabricated with 365 nm chip and different kinds of phosphors, insets (A) and (B) show the digital photos for 365 nm chip + CPS:3%Ce³⁺,3%Li⁺, insets (C) and (D) show the digital photos for 365 nm chip + CPS:3%Ce³⁺,3%Li⁺ + (Ba,Sr)₂SiO₄:Eu²⁺ + CaAlSiN₃:Eu²⁺.

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Table 3. Full set of 14 CRIs of CPS:3%Ce³⁺,3%Li⁺, (Ba,Sr)₂SiO₄:Eu²⁺, and CaAlSiN₃:Eu²⁺ with a 365 nm chip

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4. Conclusions

In this work, the Ce³⁺/Mn²⁺ doped CPS phosphors were designed by solid-state reaction method. An intense excitation band attributed to the 4f¹-4f⁰5d¹ transition of Ce³⁺ was found, which covers a broad region of 240-400 nm. Under 365 nm excitation, a blue emission band centered at 439 nm appeared for Ce³⁺, and the strongest emission intensity was obtained for x = 3%. The corresponding QE was measured to be 90.4%. The thermal stability of the CPS:3%Ce³⁺,3%Li⁺ phosphor is a little worse than that of the commercial BAM phosphor, but the CPS:3%Ce³⁺,3%Li⁺ shows a higher luminous efficiency. By comparing the spectra, it has been found that the Ce³⁺/Mn²⁺ emission bands could overlap the absorption spectra of chlorophyll a, chlorophyll b, and carotenoids in plants. The fabrication revealed the phosphors in this work could show multifunctional applications, including solid lighting and plant growth.

Funding

National Natural Science Foundation of China (No. 51602117) and National Natural Science Foundation in Higher Education of Jiangsu (No.15KJB460004).

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x (%)	τ₁ (ns)	τ₂ (ns)	A₁	A₂
0.2	18.4	42.6	772.7	3428.8
0.5	17.7	42.1	1453.5	3916.6
1	16.8	44.2	2839.0	3325.8
2	16.1	42.9	2491.3	3060.9
3	15.3	41.4	2707.2	3114.2
4	15.4	40.5	2517.7	3056.2

y (%)	τ₁ (ns)	τ₂ (ns)	A₁	A₂
0	29.7	57.0	9055.4	14750.9
0.5	29.1	56.4	10389.9	13100.0
1	26.9	54.7	9153.5	12306.3
2	23.2	52.7	10181.9	12333.8
3	19.5	49.7	9526.3	11110.2

x (%)	τ₁ (ns)	τ₂ (ns)	A₁	A₂
0.2	18.4	42.6	772.7	3428.8
0.5	17.7	42.1	1453.5	3916.6
1	16.8	44.2	2839.0	3325.8
2	16.1	42.9	2491.3	3060.9
3	15.3	41.4	2707.2	3114.2
4	15.4	40.5	2517.7	3056.2

y (%)	τ₁ (ns)	τ₂ (ns)	A₁	A₂
0	29.7	57.0	9055.4	14750.9
0.5	29.1	56.4	10389.9	13100.0
1	26.9	54.7	9153.5	12306.3
2	23.2	52.7	10181.9	12333.8
3	19.5	49.7	9526.3	11110.2

Ce³⁺/Mn²⁺-activated Ca₇(PO₄)₂(SiO₄)₂: efficient luminescent materials for multifunctional applications

Abstract

1. Introduction

2. Experimental

3. Results and discussion

4. Conclusions

Funding

References and links

Cited By

Figures (11)

Tables (3)

Equations (5)

Optics Express