Novel Ca20Al26Mg3Si3O68:Ce3+,Tb3+ phosphors: preferential site

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Novel Ca20Al26Mg3Si3O68:Ce3+,Tb3+ phosphors: preferential site occupation, color-tunable luminescence and device application Zhengce An, Haifeng Zou, Chengyi Xu, Xiangting Zhang, Rujia Dong, Ye Sheng, Keyan Zheng, Xiuqing Zhou, and Yanhua Song ACS Sustainable Chem. Eng., Just Accepted Manuscript • DOI: 10.1021/ acssuschemeng.8b05001 • Publication Date (Web): 04 Jan 2019 Downloaded from http://pubs.acs.org on January 6, 2019

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ACS Sustainable Chemistry & Engineering

Novel Ca20Al26Mg3Si3O68:Ce3+,Tb3+ phosphors: preferential site occupation, colortunable luminescence and device application Zhengce Ana, Haifeng Zou, Chengyi Xu, Xiangting Zhang, Rujia Dong, Ye Sheng, Keyan Zheng, Xiuqing Zhou, Yanhua Song*a a College

of Chemistry, Jilin University, No. 2699, Qianjin Street, Changchun 130012,

People’s Republic of China * E-mail: [email protected] (Y. S.)

Abstract A

novel

luminescence

material

of

emitting

color-tunable

Ca20Al26Mg3Si3O68(denoted as CAMSO):Ce3+,Tb3+ phosphors have been synthesized via the high temperature solid-phase reaction process. The crystal cell structure, photoluminescence properties and application performance such as thermal stability and LED device performance of the phosphors were researched in detail. CAMSO:Ce3+,Tb3+ phosphors showed multi-color with the different concentration of Ce3+ and Tb3+ ions. Although the concentration of Ce3+ ions was settled and there was the existence of energy transfer from Ce3+ to Tb3+ ions, it was found that Ce3+ ions’ blue light emission intensity showed abnormal increasing with the increase of Tb3+ ions doping concentration. The irregular phenomenon was discussed in detail. The phosphor CAMSO:0.2Ce3+, 0.1Tb3+ photoluminescence emission intensity motivated by 374nm at 150oC retained about 81% of that measured at room temperature, which demonstrating the good thermal and color stability of the sample. In addition, the white

LED

lamps

were

fabricated

through

mixing

the

sample

CAMSO:0.2Ce3+,0.2Tb3+ and the commercial phosphor CaAlSiN3:Eu2+ and their performance has been measured. The results show that this series of phosphors could be excellent candidates for the application of UV-excited w-LEDs. Keywords: abnormal luminescence, multi-crystallographic sites, tunable color, thermal stability Introduction Recently, as a clean luminescence source, white light-emitting diodes (w-LEDs) have been into people’s daily lives due to some excellent performance, for instance, high luminescence efficiency, favourable color rendering index(CRI) for coverage of visible light, lasting service life, high stability and reliability and so on.1,2 At present, the most common implementation of w-LEDs is by blue-emitting LED chips coated

ACS Paragon Plus Environment

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with an excellent yellow-light phosphor (Y,Gd)3(Al,Ga)5O12:Ce3+ (YAG:Ce3+).3,4 However, the most major drawback with this combination is the lack of red light, which will result in a cold white light together with high color temperature.5-7 Therefore, the search for suitable phosphors has become the primary target of researchers. Single matrix phosphors, particularly, have been researched widely due to excellent color reproduction characteristics and high luminous efficiency. 7-8 The single matrix white light phosphors are composed of the host crystal and doping rare earth(RE) ions. As a superior blue light component, Ce3+ ions are widely employed in white phosphors motivated by ultraviolet(UV) chips, such as Ca8La2(PO4)6O2:Ce3+/Eu2+,9 Ca5(PO4)2SiO4:Ce3+/Tb3+/Mn2+.10 In addition, Ce3+ is one of the most excellent sensitizer, which could transfer energy to activator in a single host, such as Ce3+/Tb3+, Ce3+/Eu2+, Ce3+/Mn2+, due to its 4f-5d electric dipole transition showing efficient broad band emission.11-13 Hence, in the single matrix phosphors, Ce3+ ions play an important role in color-adjusted emission to achieve the full coverage of the visible wavelength range. As a kind of excellent green-emitting activator, Tb3+ ions are usually used in luminescent materials due to its primary 5D4-7F5 transition causing a main emission peak at 545nm. Recently, many outstanding single matrix phosphors have been synthesized

and

reported,

for

example,

CaScAlSiO6:Ce3+,Tb3+,Mn2+,14

NaCaPO4:Ce3+,Tb3+,15 Ca3Ln(AlO)3(BO3)4: Ce3+,Tb3+, Mn2+ (Ln =Y, Gd )16 and so on. The luminescence intensity of Tb3+ ions will be significantly improved by co-doping Ce3+ and Tb3+ ions. Because of the great energy transfer process in different hosts from Ce3+ to Tb3+ ions, this combination is considered a new and highly-efficient multi-color-emitting component of white LEDs. In the process of energy transfer from Ce3+ to Tb3+ ions, the luminescent intensity of Ce3+ ions was usually decrease with the increase of Tb3+ concentration.15-18 However, in our system CAMSO:Ce3+, Tb3+, the luminescence regularity is different from previous research. There is a clear energy transfer phenomenon from Ce3+ to Tb3+ ions when the Ce3+/Tb3+ ions codoped concentration is less. But when we increase the co-doped concentration of these two ions, the luminescence intensity of Ce3+ ions increases notably accompanied by the increasing of Tb3+ ions, though the concentration of Ce3+ was fixed. This phenomenon is rare in other research. In this paper, we mainly discussed this rare phenomenon by some test methods and theoretical analysis from the phosphors’ luminescence properties and the samples’


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structure researched by the Rietveld refinement theory. Some excellent applied performance, like the good thermal stability and color stability, have been demonstrated by the temperature-dependent emission spectra. And the emission properties of the samples under UV excitation and the application performance on device indicated that the CAMSO phosphors have excellent potential value in nearUV w-LED application. Experimental Synthesis Synthesis of CAMSO:Ce3+/Tb3+ phosphors. All CAMSO:Ce3+/Tb3+ samples were prepared using a high temperature solid-phase synthesis method. The reactant materials contained CaCO3, Al2O3, MgO, SiO2, Ce2(CO3)3, Tb4O7, Li2CO3. All reactants purity was 99.99%. Due to Ce3+ and Tb3+ replaced Ca2+ sites in these compounds, some charge defects would appear. In order to avoid this charge defect, the same amount of Li+ ions as Ce3+/Tb3+ ions were added to the crystal lattice as a charge compensation, even if there is no special notation for simplicity in this paper. All the reactants were placed in a mortar made of agate, and mixed them with ethyl alcohol by grinding completely. After that, all raw materials were transferred to an alumina crucible. Finally, the crucible was taken to the high temperature tube furnace and sintered at 1350 oC for 2 h under keeping the reducing mixed-gases of 10%H2/90%N2. The lumpish samples after burned were ground into powders for subsequent measurement after cool to room temperature. Fabrication of the devices. For fabricating the lamps, 0.0050 g powder samples needed to mix with glue A(0.0020 g) and glue B(0.0080 g) on a glass slide, then whisk them with tweezers adequately. After aging for 30 minutes to remove minute bubbles in the mixing glue, a little amount of the mixture of glue and sample powders was dropped on the chip until a round bump came out. Finally, the packed lamps were put into a vacuum stove at 120 ºC for 2 hours. After that, the lamps were taken and cooled to room temperature for tests. Characterization Crystal representation of phosphors were identified by powder X-ray diffraction(XRD) instrument under the condition of Cu K radiation at 40 KV and 30 mA. The XRD data were collected from 10° to 80° in a 2 range with the continuous



scanning mode at a speed of 3 s per step with a step size of 0.02°. The Rietveld method was adopted to finish the Crystal structure refinement, as implemented in the General Structure Analysis System (GSAS) program. The excitation and emission spectra were measured by the machine Jobin Yvon FluoroMax-4. The luminescence decay lifetime of the phosphors were measured by 370 nm pulsed laser produced by HORIBA as the excitation source. The LED devices performance values, like color purity, Correlated Color Temperature (CCT), Color Rendering Index (CRI) and CIE chromaticity coordinates, were measured in an integrating sphere of 50 cm diameter, which was connected to a charge coupled device detector with an optical fiber (HAAS-1200, Everfine Photo-E-Info Co. Ltd). Besides temperature-dependent photoluminescence spectra and the LED device packaging process, all the measurement were performed at room temperature. Result and discussion Crystal structure analysis and simple structure description Fig.1 shows the analysis result of experimental (black crosses), calculated (red solid line), and difference (blue bottom) XRD profiles using the Rietveld refinement on the XRD pattern of the powder samples of Ca20Al26Mg3Si3O68 and Ca19.6Al26Mg3Si3O68:0.2Ce3+,0.2Li+ (denoted as CAMSO and CAMSO:0.2Ce3+, omitting Li+ for simply writing). The crystallographic data has been adopted by previously reported for CAMSO (PDF: 35-0133) as the initial structural model.19,20 From the information of CAMSO host obtained from the Rietveld refinement, the calculation structure is roughly the same as the initial model. The host lattice belongs to orthorhombic system with space group of Pmmn(59). The cell parameters are as follows: a=27.660Å, b=10.824Å, c=5.126Å, and V=1534.575Å. Comparing the data of host and that of the Ce3+ doped sample, it is obviously observed that the adulteration of Ce3+ ions doped into host has little influence to the structure parameters. The other refinement parameters are listed in Table S1. Some XRD test result of samples for pure CAMSO and Ce3+/Tb3+/Gd3+ ions doped ones together with the PDF card No.35-0133 are shown in Fig 2. It shows that the diffraction peaks are consistent with that of the standard PDF card because of the low doped concentration, indicating that the samples we prepared are pure. This result indicates a single phase has been formed and the crystal structure of the CAMSO host is almost unchanged when less amounts of other ions were doped into. But when


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more ions are doped into the matrix, the main peak splits a little. When the unit cell forms, because of the difference in ion radii between Ca2+ and other doped ions, the lattice plane would have a little change compared with matrix. Moreover, as shown in Fig.2, the XRD diffraction peaks at 2 = 30–33° are observed to shift to larger angles with an increasing concentration of doped ions. To guarantee the pure phase, the total amount of doping ions is controlled under 0.6. The unit cell of CAMSO was drawn in detail to understand the cell structure and the situation of Ca2+ sites, as shown in Fig 3. The double layer structure is displayed clearly along b axial direction. In the same layer, one side is occupied by four Ca2+ ions around six O2- anions, named Ca(I) containing Ca1 and Ca4, the other site is occupied by six Ca2+ ions around eight O2- anions, named Ca(II) containing Ca2 and Ca3, respectively, and another side exists AlO4, (Al, Si)O4 and (Mg, Al)O4 tetrahedrons.20 Multisite and luminescence properties of Ca20Al26Mg3Si3O68:Ce3+ Fig 4a shows the emission spectra of CAMSO:0.2Ce3+ excited at different wavelength about 374 and 340 nm. In this figure , it is clear to see there are two broad emission peaks at 426 and 545 nm inspired by 374 nm. They all belong to the 5d–4f transition of the Ce3+ ion.16,21 But when the sample was stimulated at 340 nm, only one emission peak appeared at 417 nm. This phenomenon can be ascribed that there are more than one emission location of Ce3+ ions in this matrix. As mentioned above, there are two coordination situations for Ca2+ ions. When Ce3+ ions replace Ca2+ ions into compounds, Ce3+ ions had two choices to enter which position. The different crystal field environment leads to the change of luminescence position. According to Uitert’s et al report, the appearance of this phenomenon has been connected with the occupation site of the Ce3+ emission and the specific local structure in different compounds, which was summarized as an empirical relationship as follows:13 𝐸(𝑐𝑚 ―1) = 𝑄[1 ― (𝑉/4)1/𝑉 ∗ 10 ―(𝑛

∗ 𝐸𝑎 ∗ 𝑟)/80

]

(1)

Where E means the emission peak position of the Ce3+ ion, Q is the energy of the free Ce3+ ion in the minimum d-band level position (Q=50000 cm-1), V is the Ce3+ ion’s valence state (V=3), n is the coordination number of the Ce3+ ion (n=6,8), Ea is the electron nucleophile of the Ca2+ ions in this matrix (eV), and r is the radius of the cation in the host replaced by the Ce3+ ion (Å). For CAMSO:Ce3+, the Ea, V, Q are



constant, and the value of E only is connected with the value of n and r. The calculated result was obtained that the emission wavelengths were 504 and 395 nm when n=6, r=1.00Å and n=8, r=1.12Å, respectively. The above discussion indicates that, when Ce3+ ions replace the Ca(I) ions, the emission spectrum is in the green area, and others positions lead to the blue emission. The asymmetric emission peak was decomposed into some well-separated Gaussian components with maxima wavelength at 413, 441, 531 and 601 nm, respectively, as shown in Fig 4b. The energy difference between 413 and 441 nm is about 1534 cm-1 and between 531 and 601 nm is about 2189 cm-1, respectively, which are highly matched with the theoretical energy difference between 2F7/2 and 2F5/2 levels (2000 cm-1).22 The excitation spectra of CAMSO:Ce3+ monitored at 426 and 545nm are shown in Fig 4c. Both excitation spectra have absorption at 374 nm. However, the spectrum monitoring at 545 nm does not have absorption at 340 nm. These are consistent with the phenomenon of the emission spectra. Combining the above information, conclusion can be drawn preliminarily that in the emission spectrum excited at 374 nm, the broad peaks of 426 nm and 545 nm belong to the eight and six coordination of Ce3+, respectively. Luminescent properties of co-doped phosphorsCAMSO:Ce3+,Tb3+ According to the previous report, an obvious energy transfer process from Ce3+ to Tb3+ ions is observed. As the doping concentration of Ce3+ is fixed, the emission intensity of Tb3+ ions increases with the increase of doped concentration, meanwhile the emission intensity of Ce3+ ions decreases gradually, until the concentration quenching phenomenon occurs.14,15 However, there is an interesting abnormal phenomenon shown in Fig 5a. When the co-doped concentration was lower, the Ce3+ emission intensity decreased at first as Tb3+ ions doped more and more due to the energy transfer process from Ce3+ to Tb3+ ions as usual. But when the Tb3+ ions concentration was higher than x=0.04, the emissions of both two ions increased with increase of doping Tb3+ ions concentration. Fig 5b shows the relative intensity variation tendency. In order to prove the existence of energy transfer from Ce3+ to Tb3+ further, we fixed the concentration of Tb3+ and changed that of Ce3+, and the emission spectra were shown in Fig S1. Obviously, with the concentration of Ce3+ ions increased, the emission intensity of Tb3+ ions increased at first, until when the Ce3+ ions doping concentration exceeded z=0.1, the concentration quenching phenomenon occurred, indicating that the energy transfer process existed between


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those two ions. We choose the samples CAMSO:0.04Ce3+,xTb3+(x=0, 0.01, 0.02, 0.03, 0.04) to calculate the value of energy transfer efficiency in each sample. The value of energy transfer efficiency can be calculated via a lot of methods, such as the following formula : I

ηT = 1 ― I0

(2)

where T is representative to the energy transfer efficiency; I and I0 are luminescence emission intensities of the Ce3+ ions whether the existence of Tb3+ ions or not. In Fig 6a, the value of energy transfer efficiency was calculated and the T value increased gradually with increasing Tb3+ ion doped concentration. Due to the Tb3+ ions concentration increasing, the distance between Ce3+ and Tb3+ ions decreased gradually, so the energy transfer from Ce3+ to Tb3+ became more and more efficient. According to a large relevant literature reported, the energy transfer process from Ce3+ to Tb3+ ions belong to multi-polar interaction. There exists the following relationship on the basis of Dexter’s energy transfer expressions of multi-polar interaction and Reisfeld’s approximation: 𝜂0 𝜂

𝑛

∝ 𝐶3

(3)

The values of 0/ can also be estimably calculated from the luminescence intensity ratio of the Ce3+ ions presence and absence Tb3+ ions (I0/I). Thus, the above formula can also be expressed as: 𝐼0 𝐼

𝑛

∝ 𝐶3

(4)

where I0 and I are representative to the emission intensities of the Ce3+ ions in the without and with of the Tb3+ ions, respectively. In this formula, when n is assigned a value as 6, 8, 10, it means the energy transfer type as, dipole–dipole (d–d), dipole– quadrupole (d-q), and quadrupole–quadrupole (q–q) interactions, respectively. The linear relationship and the values of fitting factor R2 are also shown in Fig 6b. From the picture we could inform that the energy transfer process from Ce3+ to Tb3+ ions belongs to the dipole–dipole interaction in this series of phosphors. Fig 5c shows the emission spectra of CAMSO:0.2Ce3+,xTb3+(x=0-0.4) samples. It is notable to observe that both Ce3+ and Tb3+ ions’ luminescent intensity increased accompanied by the increase of Tb3+ ions, until the concentration quenching



Page 8 of 24

happened to x = 0.4. The luminescent decay curves showed the same tendency. It is known that the process of energy transfer could influent the sensitizer’s luminescent decay lifetime, which can be fitted via a double-exponential equation:12,23 𝑡

𝐼𝑡 = 𝐼0 + 𝐴1 ∗ 𝑒

―𝜏

1

𝑡

+ 𝐴2 ∗ 𝑒

―𝜏

2

(5)

where It and I0 are the luminescence intensity at some time point and initial moment, τ1 and τ2 are the decay times for exponential components, respectively. The average lifetime values are calculated as follows: 𝐴1𝜏21 + 𝐴2𝜏22

𝜏𝑎 = 𝐴1𝜏1 + 𝐴2𝜏2

(6)

According to equation, the average lifetime for CAMSO:0.2Ce3+, xTb3+ samples with x=0, 0.1, 0.2, 0.3 and 0.4 were calculated to be 22.16, 22.35, 23.43, 28.44 and 30.34 ns, respectively, as shown in Fig 7. The excitation spectra of CAMSO:0.3Tb3+ and CAMSO:0.2Ce3+ ,0.3Tb3+ under different monitoring wavelength are shown in Fig 8a. The excitation spectrum of CAMS0:0.2Ce3+, 0.3Tb3+ monitored at 426 nm (Ce3+ emission) shows two broadband absorption peaks, whose peaks are similar to those of the CAMSO:0.2Ce3+ samples. The excitation spectrum of CAMSO:0.2Ce3+, 0.3Tb3+ monitored at 541 nm (Tb3+ emission) included both the excitation bands of these two ions, which means that the emission of Tb3+ ions are derived from Ce3+ ions emission in essence. Fig 8b shows the excitation spectra of CAMSO:0.2Ce3+, xTb3+ (x= 0-0.4) monitored at 541 nm. Obviously, the shape of spectra have a remarkable change and significant increasing at 350 nm as the concentration of Tb3+ increase. It means the enhancement of Ce3+ absorption. On the contrary, the intensity of broad peak at 440 nm decreases gradually at the same time with the increase of Tb3+ ions concentration. Combining the above mentioned, the conclusion could be obtained that, with the increase of Tb3+ ions concentration, the amount of Ce3+ ions occupying the eight coordination increases, and those occupying the six coordination decreases simultaneously. In order to explore the reason of this phenomenon, a group of samples CAMSO:0.2Ce3+, yGd3+(y=0-0.4) was prepared as a controlled experiment. Gd3+ ion and Tb3+ ion are very similar in terms of the ion radius and the number of charge, but there is no energy transfer process from Ce3+ to Gd3+ excited at 374 nm.24 As is shown in Fig 9, the luminescence intensity of Ce3+ ions increases in the blue emission zone and decreases in the green emission zone as the increases of Gd3+ ions concentration (especially when larger than 0.2 mol). Also, the excitation spectra of


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CAMSO:0.2Ce3+, yGd3+(y=0-0.4) monitored by 426 and 545 nm are shown in Fig 10. The Ce3+ ion showed its own three characteristic absorption peaks at 322, 372, and 441 nm monitored at 545 nm because of no energy transition. The intensity of these three absorption peaks decline dramatically on account of the number of Ce3+ ions decreasing at hexa-coordinate location. At the same time, the intensity of Ce3+ ions excitation peaks monitored at 426 nm increases, meaning that the number of octcoordinate location increases. The luminescence results of Ce3+-Tb3+/Gd3+ co-doped samples demonstrate that Tb3+/Gd3+ ions addition has an impact on the occupation of Ce3+.When the Tb3+/Gd3+ ions addition is a little, they have little impact on the occupation of Ce3+; but when the concentration of Tb3+/Gd3+ increase, the occupation influence of Ce3+ ions become obvious, which leads to the increase of oct-coordinate location occupation and decrease of hexa-coordinate location occupation. The following mechanism were proposed according to the above luminescence discussion combined with front research theory about the Rietveld refinement of samples of CAMSO host and CAMSO:0.2Ce3+ ,xTb3+(x=0-0.2). Because of doping Ce3+/Tb3+ ions, the average Ca–O bond length [d(Ca–O)] changed with the different concentration of that two types ions. In this host lattice, d(Ca2–O) and d(Ca3–O) are a little longer than d(Ca1–O) and d(Ca4–O), whatever Ce3+/Tb3+ ions doped or not. As some previous literature reported that the Ce–O bond length (r) is greatly affected by the crystal field environment (Dq), in other words, Dq is proportional to 1/r5.25 Therefore, it is resulting in a high energy emission when Ce3+ ions are in the looser sites corresponding to a longer bond length, which is consistent with the previous spectral discussions. As shown in Fig 11a, while d(Ca–O) changed with Tb3+ ions doped into the lattice, d(Ca2–O) was longer significantly because the occupation of Ce3+ ions increased, which would cause the emission peak shifts towards the short wavelength (blue emission). The schematic picture of the different d(Ca-O) extendretract change was shown in Fig 11b. The detailed numerical was listed in Table S3. When Ce3+ ions were doped independently, Ce3+ ions would come into Ca1–Ca4 sites at random. With the addition of Tb3+ ions doped continuously, Ce3+ ions occupy the looser positions at Ca2 or Ca3 preferentially and Tb3+ ions occupy the relatively compact position like Ca1 or Ca4 due to the Tb3+ ionic radius (0.92Å, CN=6; 1.04Å, CN=8) is smaller than that of Ce3+(1.01Å, CN=6; 1.14Å, CN=8), which is a little larger than the Ca2+ ionic radius (1.00Å, CN=6; 1.12Å, CN=8). The detailed values of the ions radius mentioned above were shown in Table S4. As mentioned above, when



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more Ce3+ ions occupy Ca2 or Ca3(eight coordination) positions, the blue emission intensity increases. This interpretation coincides with the emission spectra of CAMSO:0.2Ce3+, xTb3+. Application performance of phosphors and LED devices A series of application performance and device performance have been tested because of the apparent luminescence properties of the synthesized samples. In order to achieve the application in w-LED, it is necessary to explore some important parameters, like thermal stability. Usually, the thermal stability should be indexed from two aspects as follows: the luminescence intensity and the stability of spectral shape at different temperature.26,27 Fig 12a shows the spectra of CAMSO:0.2Ce3+, 0.1Tb3+ under various temperature from 298 to 498 K under the excitation wavelength of 374 nm. As the temperature rises, luminous intensity gradually decreases because of the molecular heat accelerating and the non - radiation transition of molecules intensifying. The luminous intensity at 423K still maintains 81% of that measured at 298K, as shown in Fig 12b. Here, Arrhenius equation is adopted to reflect the relationship between luminescence intensity and temperature as follows:28 𝐼𝑇 =

𝐼0 1+𝑐∗𝑒

(―

𝐸𝑎 𝑘𝑇

(7) )

In this equation, c is a constant term, k means Boltzmann’s constant (8.62 × 10-5 eV·K-1), I0 and IT represent the emission intensity at initial and some certain temperatures, and Ea is the activation energy for the thermal quenching. From the same sample, it is obvious that the opposite trend between IT and T. So the conclusion could be got that the intensity of luminescence decreases with the increase of temperature under normal conditions. Moreover, Fig 12c and 12d shows the Commission International de L’Eclairage (CIE) chromaticity coordinates of CAMSO:0.2Ce3+,0.1Tb3+ at different temperature, which shows excellent color stability affected little by temperature. The photographs of the corresponding sample under 365 nm lamp and 20 mA current drive are shown in the insets. The samples CAMSO:0.2Ce3+,xTb3+(x=0-0.4) were chosen to fabricate the LED lamps combined with 370 nm chips. Fig 13a shows the samples emitting color under the UV lamp at 365 nm and the LED emitting color excited by 370 nm chip at 20 mA, respectively. It is pretty straightforward to see that the emitting color changed gradually from blue to green along with the increase of Tb3+ ions doped. The CIE


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chromaticity coordinates of LED lamps was shown in Fig 13b, and other chromaticity parameters were sorted out in Table 1. Obviously, it was hopeful to realize colortunable emission from blue to cool white and finally to green in this CAMSO:0.2Ce3+, xTb3+ system, which indicated that this series of phosphors could be applied in solidstate lighting and display. However, the correlated color temperature (CCT) was on the high side due to the lack of red light ingredient in the obtained samples. Its device performance would greatly improved if mixing with commercial red powders. The sample CAMSO:0.2Ce3+,0.2Tb3+

was

mixed

with

the

commercial

red

phosphors

CaAlSiN3:Eu2+ to fabricate LED lamps. The emission spectra of the LED lamp, related color parameters and photographs of the corresponding samples were shown in Fig 14a. The CIE chromaticity coordinates of LED lamps mixed with different content of CaAlSiN3:Eu2+ and photographs of the corresponding samples were shown in Fig 14b. With the red phosphors doped constantly, the lamp emission color changed from cold white to warm white, and CCT decreased gradually at 5315K(

Novel Ca20Al26Mg3Si3O68:Ce3+,Tb3+ phosphors: preferential site

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