Ca9La(PO4)7:Eu2+,Mn2+: an emission-tunable phosphor through efficient energy transfer for white light-emitting diodes

Chien-Hao Huang; Teng-Ming Chen

doi:10.1364/OE.18.005089

1. Introduction

In recent years, white light-emitting diodes (white-LEDs) have attracted much attention, in which white light can be generated by a blue-emitting InGaN chip and yellow-emitting phosphor Y₃Al₅O₁₂:Ce³⁺ garnet (YAG:Ce³⁺). However, the disadvantages of this method are low color-rendering index (CRI, Ra = 75) and high color temperature (CCT = 7756 K) [1], due to the lack of red spectral contribution [2,3]. During the past few years, the white LEDs fabricated using (a) near ultraviolet (n-UV) LED or ultraviolet (UV) LED (350~420 nm) coupled with red, green, and blue phosphors [4–6], (b) n-UV LED (380~420 nm) pumped with a single composition green-to-red emission-tunable [7,8] and blue phosphor to improve the Ra and CCT. From this point of view, single-composition yellow-emitting (green of Eu²⁺ and red of Mn²⁺) phosphors for UV or n-UV excitations have drawn much attentions for solid state lighting. As compared to the InGaN-based blue LED chip combined with YAG:Ce³⁺ phosphor, a white-LED fabricated using a phosphor blend of single-composition emission-tunable phosphor and blue phosphor pumped with UV/NUV chips has advantages of a great Ra, tunable CCT and Commission International de I’Eclairage (CIE) chromaticity coordinates. One of the strategies for generating single-phased emission-tunable phosphor is by co-doping sensitizer and activator into the same host, which is based on the mechanism of energy transfer from sensitizer to activator. The phosphors with energy transfer mechanism of sensitizer/activator, such as Eu²⁺/Mn²⁺, have been synthesized and investigated in many hosts. For instance, Ca₂MgSi₂O₇:Eu²⁺,Mn²⁺ [7], BaMg₂Si₂O₇:Eu²⁺,Mn²⁺ [8], CaAl₂Si₂O₈:Eu²⁺,Mn²⁺ [9], SrZn₂(PO₄)₂:Eu²⁺,Mn²⁺ [10], SrMg₂(PO₄)₂:Eu²⁺,Mn²⁺ [11], KCa₁₀(PO₄)₇:Eu²⁺,Mn²⁺ [12], Ca₂P₂O₇:Eu²⁺,Mn²⁺ [13], Sr₂P₂O₇:Eu²⁺,Mn²⁺ [14], CaSiO₃:Ce³⁺,Eu²⁺,Mn²⁺ [15]. To the best of our knowledge, the crystal structure, luminescence properties and energy transfer of Eu²⁺/Mn²⁺ in Ca₉La(PO₄)₇ host have not been reported. We have firstly demonstrated a single-composition green-to-red emission-tunable Ca₉La(PO₄)₇:Eu²⁺,Mn²⁺ phosphor by energy transfer mechanism between the luminescence centers Eu²⁺ and Mn²⁺, the color can be tuned from green to yellow even to red. We have also proven that a warm white light can be achieved by increasing the dopant contents of Mn²⁺. The Ca₉La(PO₄)₇:Eu²⁺,Mn²⁺ phosphor exhibits great potential for use in white UV-LED applications to serve as a single-phased phosphor that can be pumped with near-UV or UV-LEDs.

2. Experimental

The CLP:Eu²⁺,Mn²⁺ phosphors were prepared from stoichiometric starting materials of CaCO₃(A.R. 99.9%), Y₂O₃(A.R. 99.9%), La₂O₃(A.R. 99.99%), (NH₄)₂HPO₄ (Merck ≥99%), Eu₂O₃ (A.R. 99.99%), and MnO (A.R. 99.9%). The reactant mixture was first pressed into pellets and calcined at 1,473K for 8 h under ambient atmosphere. The obtained samples were further reduced at 1,273K for 8 h under a reducing atmosphere of 15%H₂/85%N₂ in an alumina boat. The samples were characterized using powder X-ray diffraction (XRD), photoluminescence (PL) and PL excitation (PLE) spectra, decay lifetime, and CIE chromaticity, as described in our previous work [6,7]. The phase purity of CLP:Eu²⁺,Mn²⁺ phosphors was checked by using powder XRD analysis with a Bruker AXS D8 advanced automatic diffractometer with Cu Kα radiation. The measurements of PL and PLE spectra were performed by using a Spex Fluorolog-3 Spectrofluorometer (Instruments S.A., N.J., U.S.A) equipped with a 450W Xe light source and double excitation monochromators. The powder samples were compacted and excited under a 45° incidence angle and the emitted fluorescence was detected by a Hamamatsu Photonics R928 type photomultiplier perpendicular to the excitation beam. Time-resolved measurements were performed with a tunable nanosecond optical-parametric-oscillator/Q-switch-pumped YAG:Nd³⁺ laser system (NT341/1/UV, Ekspla). Emission transients were collected with a nanochromater (SpectraPro-300i, ARC), detected with photomultiplier tube (R928HA, Hamamatsu), connected to a digital oscilloscope (LT372, LeCrop) and transferred to a computer for kinetics analysis.

White LED lamps were fabricated by integrating a mixture of transparent silicon resin and phosphors blend of Ca₉La(PO₄)₇:0.005Eu²⁺,0.015Mn²⁺ and BaMgAl₁₀O₁₇:Eu²⁺ commodity on an UV-chip (AOT Product No: DC0004CAA, Spec: 370U02C, wavelength peak: 365 ~370 ± 0.6 nm, chip size: 40x40 mil, forward voltage: 3.8 ~4.0 ± 0.02 V, power: 10-20 ± 0.21 mW). The Commission International de I’Eclairage (CIE) chromaticity coordinates for all samples were measured by a Laiko DT-101 color analyzer equipped with a CCD detector (Laiko Co., Tokyo, Japan).

3. Results and discussion

All powder XRD patterns of Ca₉Y(PO₄)₇ (CYP) and CLP:Eu²⁺,Mn²⁺ phosphors are shown in Fig. 1 . All phases purity of the as-prepared phosphors was analyzed with JCPDS No. 46-0402 [16] as a reference, indicating that the doped Eu²⁺ ions or co-doped Eu²⁺/Mn²⁺ ions have not caused any observable change in the CLP host structure. The compound Ca₉La(PO₄)₇ is iso-structural to the Ca₉Y(PO₄)₇ [16] and β-Ca₉In(PO₄)₇ [17], Ca₉Y(PO₄)₇ has a rhombohedral crystal structure with a space group of R3c (No.161), and their lattice parameters are a = 10.4442Å, c = 37.324 Å, V = 3525.89 nm³, Z = 6 and Ca²⁺, Y³⁺ (La³⁺) and P⁵⁺ ions are have three, one and three crystallographic sites, respectively. The coordination environment of the cations is such that Ca(1) and Ca(2) are eight-coordinated, Ca(3) is nine-coordinated, Y (La) is six-coordinated and P(1), P(2), and P(3) are four-coordinated to oxygen atoms. The ionic radii for eight- and nine-coordinated Eu²⁺ are 1.25 and 1.3 Å, respectively, and that for eight-coordinated Mn²⁺ is 0.96 Å; however, the ionic radii for eight- and nine-coordinated Ca²⁺ cations are 1.12 and 1.18 Å, respectively. Therefore, based on comparison of the effective ionic radii of cations with different coordination numbers, we have proposed that Eu²⁺ and Mn²⁺ are expected to randomly occupy the Ca²⁺ sites in the host structure.

Fig. 1 Powder XRD patterns of Ca₉Y(PO₄)₇, Ca₉La(PO₄)₇, Ca₉La(PO₄)₇:Eu²⁺ and Ca₉La(PO₄)₇:Eu²⁺,Mn²⁺ (JCPDS No. 46-0402).

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Figure 2 shows the emission spectra of (Ca_0.99)₉(Y_1-yLa_y)(PO₄)₇:0.01Eu²⁺ with varying amount of La³⁺ ion concentrations. The PL intensity of (Ca_0.99)₉(Y_1-yLa_y)(PO₄)₇:0.01Eu²⁺ phosphor was found to decrease with increasing La⁺³Ion concentration and the blue-greenish emission band centering at 485 nm (sample with y = 0) was observed to red shift to green emission centering at 502 nm (sample with y = 1) with increasing La⁺³Ion concentration. According to the reports from Robertson et al. [18] and Jang et al. [19], crystal field splitting (Dq) is expressed as the following equation [20]:

D q = \frac{1}{6} Z e^{2} \frac{r^{4}}{R^{5}}

where Dq is a measure of the energy level separation, Z is the anion charge, e is an electron charge, r is the radius of d wavefunction, and R is the bond length. When Y³⁺ site was substituted and occupied by a larger La³⁺ ion, the distance between Eu²⁺ and O^2- became shorter. Since crystal field splitting is proportional to 1/R⁵, this shorter Eu²⁺ O^2- distance also increases the magnitude of crystal field, so that it results in lowering of the 5d band of Eu²⁺.

Fig. 2 The PL spectra of (Ca_0.99)₉(Y_1-yLa_y)(PO₄)₇:0.01Eu²⁺ with varying La³⁺ contents. The inset shows λ_em and relative intensity as a function of y for (Ca_0.99)₉(Y_1-yLa_y)(PO₄)₇:0.01Eu²⁺ excited at 365 nm.

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The concentration dependence of relative PLE and PL intensity of CLP:xEu²⁺ (x = 0.001 ~0.1) under 365 nm excitation was shown in Fig. 3 . The PL spectra exhibited a broad band green emission centered at 502 nm, which was imputed to the 4f ⁶5d ¹ → 4f ⁷ of the Eu²⁺ ion. The optimal Eu²⁺ dopant content was found to be 0.005 mole and the PL/PLE intensity was observed to increase with increasing x when x < 0.005. For samples with Eu²⁺ dopant content higher than 0.005 moles, concentration quenching was observed and the PL/PLE intensity was found to decrease with increasing doped Eu²⁺ content.

Fig. 3 Concentration dependence of relative PLE and PL intensity of CLP: xEu²⁺ (x = 0.001~0.1) under 365 nm excitation.

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As indicated in Fig. 4(a) , the Eu²⁺ emission of CLP:Eu²⁺ (solid line) at 400-600nm and centered at 502 nm (solid line) was assigned to the 4f ⁶5d ¹ → 4f ⁷ transition and the Mn²⁺ excitation of CLP:Mn²⁺ contains several bands centered at 267, 343, 370, 405, 417, and 454 nm (dash line), corresponding to the transitions from the ⁶A₁(⁶S) ground state to the excited states of ⁴T₁(⁴P), ⁴E(⁴D), ⁴T₂(⁴D), [⁴A₁(⁴G), ⁴E(⁴G)], ⁴T₂(⁴G), and ⁴T₁(⁴G) levels, as reported by Ravikumar et al. [21]. We have observed a significant spectral overlap at around 454 nm between the Eu²⁺ PL and Mn²⁺ PLE spectra, which revealed that the spectral overlap is matched for Eu²⁺ and Mn²⁺ and a part of the energy can transfer from Eu²⁺ to Mn²⁺. Therefore, there can be a good energy transfer from Eu²⁺ to Mn²⁺ in CLP:Eu²⁺,Mn²⁺ and an effective resonance-type energy transfer from Eu to Mn (ET_Eu→Mn) was expected. Figure 4(b) shows the emission spectra of CLP:0.005Eu²⁺,xMn²⁺ phosphors (x = 0, 0.01, 0.015, 0.03, 0.05, 0.07 and 0.1). For CLP:0.005Eu²⁺,xMn²⁺ samples with 0.01 ≤ x ≤ 0.1, two broad emission bands centered at 502 nm and 635 nm were observed, respectively. The emission band at 502 nm is viewed as the typical Eu²⁺ emission and the band at 635 nm is due to the Mn²⁺ emission. The PL intensity of Eu²⁺ at 502 nm was found to decrease with increasing Mn²⁺ content, and the PL intensity of Mn²⁺ at 635 nm increases with increasing Mn²⁺ content until the appearance of concentration quenching occurred at the sample with Mn²⁺ content of 0.07, which further supports the occurrence of the ET_Eu→Mn mechanism. Moreover, the observed variation of emission-tunable PL intensities of Eu²⁺ and Mn²⁺ in CLP:0.005Eu²⁺,xMn²⁺ strongly support energy transfer from Eu²⁺ to Mn²⁺.

Fig. 4 (a) Spectral overlap between the Eu²⁺ PL spectrum of CLP:Eu²⁺ (solid line) and the PLE spectrum of CLP:Mn²⁺ (dash line); (b) The emission spectra of CLP:0.005Eu²⁺, xMn²⁺ phosphors excited at 365 nm.

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Table 1 reports the chemical compositions and the chromaticity coordinates of CLP:0.005Eu²⁺,xMn²⁺ phosphors and Fig. 5 further represents the data in the 1931 CIE chromaticity diagram. The chromaticity coordinates of CLP:0.005Eu²⁺,xMn²⁺ ranging from (0.282, 0.445) to (0.406, 0.388) and eventually to (0.637, 0.303), indicate that the color hue is tunable from green to yellow and, eventually, to red in the visible spectral region by changing the doped Mn²⁺ content. A white light with chromaticity coordinates (0.353, 0.324) was generated by a phosphor blend of a yellow-emitting CLP:0.005Eu²⁺,0.015Mn²⁺ and a blue-emitting BaMgAl₁₀O₁₇:Eu²⁺ (BAM:Eu²⁺). For comparison, the YAG:Ce³⁺ with CIE chromaticity of (0.429, 0.553) pumped with an InGaN blue chip with chromaticity of (0.144, 0.030) can give white light with chromaticity of (0.291, 0.300) [22]. The inset of Fig. 5 shows three LEDs fabricated by pumping phosphors of CLP:0.005Eu²⁺ (photo 1), a mixture of CLP:0.005Eu²⁺,0.015Mn²⁺ and blue BAM:Eu²⁺ (photo w), and CLP:0.005Eu²⁺,0.1Mn²⁺ (point 7), respectively, with a 365 nm UV-chip under a forward bias of 350 mA.

Table 1. Comparison of CIE chromaticity coordinates for CLP:0.005Eu²⁺,xMn²⁺ phosphors (λ_ex = 365 nm) and simulated white light using Y₃Al₅O₁₂:Ce³⁺ phosphors (λ_ex = 460 nm).

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Fig. 5 CIE chromaticity diagram of (Ca_0.995-x)₉La(PO₄)₇:0.005Eu²⁺,xMn²⁺ phosphors excited at 365 nm: x = (1) 0, (2) 0.01, (3) 0.015, (4) 0.03, (5) 0.05, (6) 0.07, and (7) 0.1.

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The decay curves of CLP:0.005Eu²⁺,xMn²⁺ phosphors were measured and represented as shown in Fig. 6. The corresponding luminescence decay times can be best fitted with a second-order exponential decay mode (Fig. 6 dash line) by the following equation [23,24]:

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

where I is the luminescence intensity; A₁ and A₂ are constants; t is the time; and τ₁ and τ₂ are rapid and slow lifetimes for exponential components. Using these parameters, the average decay times (τ) can be determined by the formula given in the following [25]:

〈 τ 〉 = (A_{1} τ_{1}^{2} + A_{2} τ_{2}^{2}) / (A_{1} τ_{1} + A_{2} τ_{2})

The values of τ₁, τ₂, A₁ and A₂ are analyzed, determined, and summarized in Table 2 , which indicates that in solely Eu²⁺-activated system, the average decay time is long. However, in the Eu²⁺/Mn²⁺ co-doped system, the average decay time was found to be shortened with increasing doped Mn²⁺ content. Similar observations could be attributed to the formation of paired Mn²⁺ centers with faster decay than single Mn²⁺ centers, as proposed by Ruelle et al. [25] The average decay times (τ) were calculated to be 838, 768, 611, 424, 132, 55.7, and 25.8 ns for CLP:0.005Eu²⁺,xMn²⁺ with x = 0, 0.01, 0.015, 0.03, 0.05, 0.07, and 0.1, respectively. The inset of Fig. 6 clearly shows the relation between energy transfer efficiency (η_T) and concentration of Mn²⁺ ions. The η_T from Eu²⁺ to Mn²⁺ can be expressed according to Paulose et al. [26]

η_{T} = 1 - \frac{τ_{S}}{τ_{S 0}}

where τ_S is the lifetime of Eu²⁺ in the presence of Mn²⁺ and τ_S0 is the lifetime of the sensitizer Eu²⁺ in the sample in the absence of Mn²⁺. The η_T was determined to be 0%, 18.2%, 41.9%, 59.7%, 81.1%, 89.8% and 95.6% for CLP:0.005Eu²⁺,xMn²⁺ with x = 0, 0.01, 0.015, 0.03, 0.05, 0.07, and 0.1, respectively. These results indicate that the η_T of CLP:0.005Eu²⁺,xMn²⁺ increases with increasing Mn²⁺ dopant content.

Table 2. Decay times of CLP:0.005Eu²⁺,xMn²⁺ phosphors excited at 365 nm with emission monitored at 502 nm.

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Based on Dexter’s energy transfer formula of multi-polar interaction and Reisfeld’s approximation, the following relation can be obtained [27,28]:

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

where C is Mn²⁺ ions concentration. As (τ_S0/τ_S)∝C^α/3 with α = 6, 8, and 10 corresponds to dipole-dipole, dipole-quadrupole, and quadrupole-quadrupole interaction, respectively. The relationship of (τ_S0/τ_S)∝C^α/3 was illustrated in Fig. 7 and a linear behavior was observed only when α = 8, so that energy absorbed by Eu²⁺ is transferred to Mn²⁺ by a nonradiative dipole-quadrupole mechanism. The above results indicate that energy transfer occurs between Eu²⁺ and Mn²⁺ in CLP:Eu²⁺,xMn²⁺ phosphor and the relative intensity of green and red emission could be tuned by adjusting the relative concentration of Eu²⁺ and Mn²⁺, respectively.

Fig. 7 Dependence of τ_S0/τ_S of Eu²⁺ on (a) C^6/3 , (b) C^8/3 and (c) C^10/3.

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According to dipole-quadrupole mechanism, the critical distance of energy transfer from a sensitizer Eu²⁺ to an activator Mn²⁺ is given by:

P_{E u - M n}^{D Q} = 0.63 \times 10^{28} \frac{f_{q} λ_{s}^{2} Q_{a}}{τ_{S 0} R_{E u - M n}^{8} f_{d} E_{s}^{4}} \int F_{s} (E) F_{a} (E) d E

where Q_a = 4.8 × 10⁻¹⁶ and f_d is the absorption coefficient of Mn²⁺; f_d = 10⁻⁷ and f_q = 10⁻¹⁰ are the oscillator strengths of dipole and quadrupole electrical absorption transitions for Mn²⁺; λ_S (Å) and E (eV) are the emission wavelength and emission energy of Eu²⁺, and ∫F_S(E)F_a(E)dE represents the spectral overlap between the Eu²⁺ and Mn²⁺ and it was estimated be 1.3565eV⁻¹ [29]. The critical distance R_c of energy transfer from Eu²⁺ to Mn²⁺ is defined as the distance for which the probability of transfer equals the probability of radiative emission of Eu²⁺, i.e., the distance for which

P_{E u - M n}^{D Q} τ_{S 0}^{} = 1

. Therefore, R_c can be calculated using the following equation [29,30]:

R_{c}^{8} = 0.63 \times 10^{28} \frac{f_{q} λ_{s}^{2} Q_{a}}{f_{d} E_{s}^{4}} \int F_{s} (E) F_{a} (E) d E

In this system, the critical distance of energy transfer in CLP:Eu²⁺,Mn²⁺ phosphor was calculated to be about 11.36 Å, which is similar to those obtained for Ca₂MgSi₂O₇:Eu²⁺/Mn²⁺ (11.97 Å) [7] and Sr₂Zn(PO₄)₂:Eu²⁺/Mn²⁺ (11.4 Å) [10].

Figure 8 shows the PL spectra of CLP:0.005Eu²⁺,0.015Mn²⁺ (black line), BAM:Eu²⁺ commodity (blue line) and a blend of yellow CLP:0.005Eu²⁺,0.015Mn²⁺ and blue-emitting BAM:Eu²⁺ (dash line) commodity pumped with a UV-LED chip (365 nm). Shown in Fig. 9 is the EL spectrum of a white LED lamp fabricated with the above-stated phosphor blend and silicon resin pumped with a 365 nm UV-LED chip and driven with a 350-mA current. The white light generated shows CIE color coordinates (0.35,0.31) and Ra of 91.5, as determined from the full set of the 8 CRIs average Ra values shown in Table 3 . The upper-right inset of Fig. 9 shows the appearance of a phosphor-converted LED lamp under a forward bias of 350 mA. These results demonstrated that our phosphor blend (CLP:Eu,Mn and BAM:Eu²⁺)-converted white-light UV-LED shows higher Ra value (91.5) and lower CCT (4,496K) than those (i.e., Ra = 75, CCT = 7756K) of a white LED fabricated with YAG:Ce³⁺ phosphor pumped with blue InGaN chip [1].

Fig. 8 The PL spectrum of (Ca_0.98)₉La(PO₄)₇:0.005Eu²⁺,0.015Mn²⁺, BaMgAl₁₀O₁₇:Eu²⁺ and the white-emitting phosphors of a mixture of (Ca_0.98)₉La(PO₄)₇:0.005Eu²⁺,0.015Mn²⁺ and BaMgAl₁₀O₁₇:Eu²⁺.

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Fig. 9 EL spectrum of a white LED lamp fabricated using a UV-chip (365 nm) and a phosphor blend of (Ca_0.98)₉La(PO₄)₇:0.005Eu²⁺,0.015Mn²⁺ and BaMgAl₁₀O₁₇:Eu²⁺ under a forward bias of 350 mA.

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Table 3. Full set of the 8 CRIs and the Ra values of (Ca_0.98)₉La(PO₄)₇:0.005Eu²⁺,0.015Mn²⁺ and BAM:Eu²⁺ with a 365 nm UV-LED

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4. Conclusion

In conclusion, a series of single-composition emission-tunable CLP:Eu²⁺,Mn²⁺ phosphors were synthesized and investigated. The energy transfer from sensitizer Eu²⁺ to activator Mn²⁺ in Ca₉La(PO₄)₇ host has been studied and demonstrated to be a resonant type via a dipole-quadrupole mechanism based on the decay lifetime data and the energy transfer critical distance was estimated to be 11.36 Å by using the spectral overlap method. We have improved the Ra and reduced CCT value of white LEDs by using a phosphor blend of yellow-emitting Ca₉La(PO₄)₇:0.005Eu²⁺,0.015Mn²⁺ and blue-emitting BaMgAl₁₀O₁₇:Eu²⁺ commodity pumped with UV-LED chip (365 nm). Our investigation results indicate that the warm white-emitting UV-LED based on phosphor blend of CLP:Eu,Mn and BAM:Eu²⁺ exhibits superior Ra and CCT to those of conventional white LED based on YAG:Ce³⁺ pumped with blue LED chips.

Acknowledgments

This research was supported by National Science Council of Taiwan (ROC) under contract No. NSC98-2113-M-009-005-MY3 (T.-M. C.) and, in part, by Industrial Technology Research Institute under contract No. 7301XS1861 (C.-H. H.).

References and links

1. H. S. Jang, Y. H. Won, and D. Y. Jeon, “Improvement of electroluminescent property of blue LED coated with highly luminescent yellow-emitting phosphors,” Appl. Phys. B 95(4), 715–720 (2009). [CrossRef]

2. A. A. Setlur, W. J. Heward, Y. Gao, A. M. Srivastava, R. G. Chandran, and M. V. Shankar, “Crystal chemistry and luminescence of Ce³⁺-doped Lu₂CaMg₂(Si,Ge)₃O₁₂ and its use in LED based lighting,” Chem. Mater. 18(14), 3314–3322 (2006). [CrossRef]

3. M. Batentschuk, A. Osvet, G. Schierning, A. Klier, J. Schneider, and A. Winnacker, “Simultaneous excitation of Ce³⁺ and Eu³⁺ ions in Tb₃Al₅O₁₂,” Radiat. Meas. 38(4-6), 539–543 (2004). [CrossRef]

4. Z. Hao, J. Zhang, X. Zhang, X. Sun, Y. Luo, S. Lu, and X.- Wang, “White light emitting diode by using α-Ca₂P₂O₇:Eu²⁺, Mn²⁺ phosphor,” Appl. Phys. Lett. 90(26), 261113 (2007). [CrossRef]

5. J. S. Kim, P. E. Jeon, Y. H. Park, J. C. Choi, H. L. Park, G. C. Kim, and T. W. Kim, “White-light generation through ultraviolet-emitting diode and white-emitting phosphor,” Appl. Phys. Lett. 85(17), 3696 (2004). [CrossRef]

6. W. J. Yang and T. M. Chen, “Ce³⁺/Eu²⁺ codoped Ba₂ZnS₃: a blue radiation-converting phosphor for white light-emitting diodes,” Appl. Phys. Lett. 90(17), 171908 (2007). [CrossRef]

7. C. K. Chang and T. M. Chen, “White light generation under violet-blue excitation from tunable green-to-red emitting Ca₂MgSi₂O₇:Eu,Mn through energy transfer,” Appl. Phys. Lett. 90(16), 161901 (2007). [CrossRef]

8. G. Q. Yao, J. H. Lin, L. Zhang, G. X. Lu, M. L. Gong, and M. Z. Su, “Luminescent properties of BaMg₂Si₂O₇:Eu²⁺,Mn²⁺,” J. Mater. Chem. 8(3), 585–588 (1998). [CrossRef]

9. W. J. Yang, L. Luo, T. M. Chen, and N. S. Wang, “Luminescence and energy transfer of Eu- and Mn-coactivated CaAl₂Si₂O₈ as a potential phosphor for white-Light UVLED,” Chem. Mater. 17(15), 3883–3888 (2005). [CrossRef]

10. W. J. Yang and T. M. Chen, “White-light generation and energy transfer in SrZn₂(PO₄)₂:Eu,Mn phosphor for ultraviolet light-emitting diodes,” Appl. Phys. Lett. 88(10), 101903 (2006). [CrossRef]

11. C. Guo, L. Luan, X. Ding, and D. Huang, “Luminescent properties of SrMg₂(PO₄)₂:Eu²⁺,and Mn²⁺ as a potential phosphor for ultraviolet light-emitting diodes,” Appl. Phys., A Mater. Sci. Process. 91(2), 327–331 (2008). [CrossRef]

12. W. R. Liu, Y. C. Chiu, Y. T. Yeh, S. M. Jang, and T. M. Chen, “Luminescence and energy transfer mechanism in Ca₁₀K(PO₄)₇:Eu²⁺, Mn²⁺ phosphor,” J. Electrochem. Soc. 156(7), J165 (2009). [CrossRef]

13. Z. Hao, J. Zhang, X. Zhang, S. Lu, Y. Luo, X. Ren, and X. Wang, “Phase dependent photoluminescence and energy transfer in Ca₂P₂O₇:Eu²⁺, Mn²⁺ phosphors for white LEDs,” J. Lumin. 128, 941 (2008).

14. S. Ye, Z. S. Liu, J. G. Wang, and X. P. Jing, “Luminescent properties of Sr₂P₂O₇:Eu,Mn phosphor under near UV excitation,” Mater. Res. Bull. 43(5), 1057–1065 (2008). [CrossRef]

15. S. Ye, X. M. Wang, and X. P. Jing, “Energy transfer among Ce³⁺, Eu²⁺, and Mn²⁺ in CaSiO₃,” J. Electrochem. Soc. 155(6), J143 (2008). [CrossRef]

16. JCPDS No. 46–0402.

17. V. A. Morozov, A. A. Belik, S. Yu. Stefanovich, V. V. Grebenev, O. I. Lebedev, G. Van Tendeloo, and B. I. Lazoryak, “High-temperature phase transition in the whitlockite-type phosphate Ca₉In(PO₄)₇,” J. Solid State Chem. 165(2), 278–288 (2002). [CrossRef]

18. J. M. Robertson, M. W. van Tol, W. H. Smits, and J. P. H. Heyene, “Colourshift of the Ce³⁺ emission in monocrystalline epitaxially grown garnet layers,” Philips J. Res. 36, 15 (1981).

19. H. S. Jang, W. B. Im, D. C. Lee, D. Y. Jeon, and S. S. Kim, “Enhancement of red spectral emission intensity of Y₃Al₅O₁₂:Ce³⁺ phosphor via Pr co-doping, and Tb substitution for the application to white LEDs,” J. Lumin. 126(2), 371–377 (2007). [CrossRef]

20. P. D. Rack and P. H. Holloway, “The structure, device physics, and material properties of thin film electroluminescent displays,” Mater. Sci. Eng. Rep. 21(4), 171–219 (1998). [CrossRef]

21. R. V. S. S. N. Ravikumar, K. Ikeda, A. V. Chandrasekhar, Y. P. Reddy, P. S. Rao, and J. Yamauchi, “Site symmetry of Mn(II) and Co(II) in zinc phosphate glass,” J. Phys. Chem. Solids 64(12), 2433–2436 (2003). [CrossRef]

22. C. C. Chiang, M. S. Tsai, and M. H. Hon, “Synthesis and photoluminescent properties of Ce³⁺ doped terbium aluminum garnet phosphors,” J. Alloy. Comp. 431(1-2), 298–302 (2007). [CrossRef]

23. R. Pang, C. Li, L. Shi, and Q. Su, “A novel blue-emitting long-lasting proyphosphate phosphor Sr₂P₂O₇:Eu²⁺,Y³⁺,” J. Phys. Chem. Solids 70(2), 303–306 (2009). [CrossRef]

24. S. Buddhudu, M. Morita, S. Murakami, and D. Rau, “Temperature-dependent luminescent and energy transfer in europium and rare earth codoped nanostructured xerogel and sol-gel silica glasses,” J. Lumin. 83–84(1-3), 199–203 (1999). [CrossRef]

25. N. Ruelle, M. P. Thi, and C. Fouassier, “Cathodoluminescent properties and energy transfer in red calcium sulfide phosphors (CaS:Eu,Mn),” Jpn. J. Appl. Phys. 31(Part 1, No. 9A), 2786–2790 (1992). [CrossRef]

26. P. I. Paulose, G. Jose, V. Thomas, N. V. Unnikrishnan, and M. K. R. Warrier, “Sensitized fluorescence of Ce³⁺/Mn²⁺ system in phosphate glass,” J. Phys. Chem. Solids 64(5), 841–846 (2003). [CrossRef]

27. H. Jiao, F. Liao, S. Tian, and X. J. Jing, “Luminescent properties of Eu³⁺ and Tb³⁺ activated Zn₃Ta₂O₈,” J. Electrochem. Soc. 150(9), H220 (2003). [CrossRef]

28. Y. Tan and C. Shi, “Ce³⁺ → Eu²⁺ energy transfer in BaLiF₃ phosphor,” J. Phys. Chem. Solids 60(11), 1805–1810 (1999). [CrossRef]

29. G. Blasse, “Energy transfer in oxidic phosphors,” Philips Res. Rep. 24, 131 (1969).

30. D. L. Dexter, “A theory of sensitized luminescence in solids,” J. Chem. Phys. 21(5), 836 (1953). [CrossRef]

Point No. in chromaticity diagram	Sample composition	(x, y)
1	x = 0.000	(0.281, 0.445)
2	x = 0.010	(0.367, 0.411)
3	x = 0.015	(0.406, 0.388)
4	x = 0.030	(0.495, 0.358)
5	x = 0.050	(0.573, 0.328)
6	x = 0.070	(0.620, 0.310)
7	x = 0.100	(0.637, 0.303)
w	CLP:0.005Eu²⁺,0.015Mn²⁺ + BAM:Eu²⁺	(0.353, 0.324)
a	blue InGaN LED	(0.144, 0.030)
b	blue LED/Y₃Al₅O₁₂:Ce³⁺	(0.291, 0.300)
c	Y₃Al₅O₁₂:Ce³⁺	(0.429, 0.553)

Samples	τ₁	A₁	τ₂	A₂	τ(ns)
x = 0.000	1.79E-7	0.74	9.62E-7	0.73	838
x = 0.010	1.52E-7	0.75	8.78E-7	0.73	768
x = 0.015	9.12E-8	1.89	7.76E-7	0.70	611
x = 0.030	6.57E-8	4.06	6.60E-7	0.61	424
x = 0.050	4.19E-8	18.65	4.54E-7	0.48	132
x = 0.070	3.49E-8	45.50	3.57E-7	0.31	55.7
x = 0.100	2.57E-8	118.38	2.58E-8	118.21	25.8

Point No. in chromaticity diagram	Sample composition	(x, y)
1	x = 0.000	(0.281, 0.445)
2	x = 0.010	(0.367, 0.411)
3	x = 0.015	(0.406, 0.388)
4	x = 0.030	(0.495, 0.358)
5	x = 0.050	(0.573, 0.328)
6	x = 0.070	(0.620, 0.310)
7	x = 0.100	(0.637, 0.303)
w	CLP:0.005Eu²⁺,0.015Mn²⁺ + BAM:Eu²⁺	(0.353, 0.324)
a	blue InGaN LED	(0.144, 0.030)
b	blue LED/Y₃Al₅O₁₂:Ce³⁺	(0.291, 0.300)
c	Y₃Al₅O₁₂:Ce³⁺	(0.429, 0.553)

Samples	τ₁	A₁	τ₂	A₂	τ(ns)
x = 0.000	1.79E-7	0.74	9.62E-7	0.73	838
x = 0.010	1.52E-7	0.75	8.78E-7	0.73	768
x = 0.015	9.12E-8	1.89	7.76E-7	0.70	611
x = 0.030	6.57E-8	4.06	6.60E-7	0.61	424
x = 0.050	4.19E-8	18.65	4.54E-7	0.48	132
x = 0.070	3.49E-8	45.50	3.57E-7	0.31	55.7
x = 0.100	2.57E-8	118.38	2.58E-8	118.21	25.8

Ca₉La(PO₄)₇:Eu²⁺,Mn²⁺: an emission-tunable phosphor through efficient energy transfer for white light-emitting diodes

Abstract

1. Introduction

2. Experimental

3. Results and discussion

4. Conclusion

Acknowledgments

References and links

Cited By

Figures (8)

Tables (3)

Equations (7)

Optics Express