Synthesis and luminescent properties of KGd(MoO4)2:Sm3+ red phosphor for white light emitting diodes

Materials Research Bulletin 90 (2017) 66–72

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Synthesis and luminescent properties of KGd(MoO4)2:Sm3+ red phosphor for white light emitting diodes Qiang Ren, Fei Lin* , Xiulan Wu, Ou Hai, Tengyue Wei, Yehui Jiao, Huanhuan Li School of Materials Science and Engineering, Shaanxi University of Science & Technology, Xi’an, 710021, PR China

A R T I C L E I N F O

Article history: Received 8 November 2016 Received in revised form 13 February 2017 Accepted 13 February 2017 Available online 16 February 2017 Keywords: Rare earth doping Red phosphor KGd(MoO4)2 Luminescent properties

A B S T R A C T

The red-emitting phosphors of Sm3+ ions doped KGd(MoO4)2 were synthesized by a high temperature solid state reaction method. The X-ray diffraction patterns confirmed that the principal crystalline phase of the sample was KGd(MoO4)2. The photoluminescence (PL) excitation spectra of KGd(MoO4)2:Sm3+ showed a series of absorption peaks in the range of 300–500 nm and the strongest excitation peak at 406 nm due to 6H5/2 ! 4F7/2 transition of Sm3+. The PL spectrum indicated that the optimum dopant concentration of Sm3+ ion is 0.06. The critical transfer distance of Sm3+ ions was 17.65 Å and the quenching mechanism of KGd(MoO4)2:Sm3+ determined electric dipole–dipole interaction. The CIE chromaticity coordinates of the KGd(MoO4)2:0.06Sm3+ phosphor was located in the red region. All decay curves well fitted by the double exponential function, and average lifetimes for the 4G5/2 excited level of Sm3+ in the KGd(MoO4)2 was in the submicrosecond. And the quantum efficiency was determined to be 28.5%. © 2017 Elsevier Ltd. All rights reserved.

1. Introduction The white light-emitting diodes (WLED) have potential to replace traditional light sources (incandescent light bulb and fluorescent lamp) and develop other new applications, because of their numerous of advantages, such as high efficiency, low-cost, energy-saving, long lifetime, excellent stability, environmentally friendly, which indicates that the WLED will become a new generation solid state lighting [1–3], WLED can be achieved in mainly two ways: the first way is blue LED chips excite yellow emitting phosphors, and the second one is ultraviolet light (UV) or near ultraviolet light (NUV) LED chips excite green, blue and red phosphors to obtain white light. In the first way, the absence of red emitting leads to low color rendering index (CRI) and poor luminescent properties. In the second way, ultraviolet light (UV) or near ultraviolet light (NUV) LED chips are able to excite green and blue phosphors have been very mature in recent years, but red phosphors are not mature enough in a practical application, such as, the physical and chemical performance of sulfide system is unstable, which prone to deliquesce produced strong corrosion of H2S causes the LEDs chip was corroded, damaged and harmful to the environment and so on [4–6]. And Eu3+- or Sm3+-doped nitride

* Corresponding author. E-mail address: [email protected] (F. Lin). http://dx.doi.org/10.1016/j.materresbull.2017.02.023 0025-5408/© 2017 Elsevier Ltd. All rights reserved.

which have high red-emission intensity and stability are widely noted, but high calcination temperature (1500  C–2000  C) and perpetual continuous nitrogen atmosphere on calcining process lead to high cost which restrict production [7–10]. Therefore, the priority in developing novel phosphors have more important practical significance. Trivalent rare earth (RE) ions have various of energy levels can make light of different colors in different light stimulate. Europium ion (Eu3+ ion), Samarium ion (Sm3+ ion), Praseodymium ion (Pr3+ ion) can get red or orange-red light under UV- or NUV-light when doped in different matrix materials. Especially Sm3+ ion, it has four dominant emissions of yellow (565 nm), orange-red (600 nm), red (648 nm) and deep red (720 nm), which are attributed to the 4G5/2 ! 6H5/2, 4G5/2 ! 6H7/2, 4G5/2 ! 6H9/2 and 4G5/2 ! 6H11/2 transitions [11–14]. Hence, Sm3+-doped phosphor can implement red or orange-red phosphors with low color temperature and high CRI in warm WLED [15–17]. As is well known, the molybdate has a typical structure of scheelite with good thermostability and physical or chemical stability, and Mo6+ ion is encompassed O2 ion in MoO42 group to form a symmetrical stable tetrahedral structure. As the host matrix, the MoO42 group hasa broad absorption band in the ultraviolet light and the energy of MoO42 group can easily transfer to rare earth ion, thus enhancing quantum efficiency of RE ions doped in matrix [18–20]. In recent years, there are many related reports are available in rare earth doped molybdate red phosphors, such as LiY(MoO4)2:Pr3+ [21], LiLa

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(MoO4)2:Eu3+ [22], NaY(MoO4)2:Eu3+ [23] and CaLa2(MoO4)4:Eu3+ [24], but there is no report about KGd(MoO4)2:Sm3+ phosphor. In this paper, Sm3+ -doped KGd(MoO4)2 phosphor was synthesized by a high temperature solid state method. The luminescent properties of this phosphor were studied by photoluminescence excitation spectrum, photoluminescence emission spectrum, concentration quenching, CIE and decay curve. 2. Experimental The KGd(MoO4)2:Sm3+ phosphors (The Sm3+ mole concentration is 0.02, 0.06, 0.08 or 0.10) were prepared by a high temperature solid state method. The raw materials were potassium carbonate (K2CO3, AR), gadolinium oxide (Gd2O3, 4N), molybdenum oxide (MoO3, AR) and samarium oxide (Sm2O3, 4N). According to the stoichiometric molar ratio of KGd(MoO4)2:Sm3+, the raw materials were weighted accurately and put in agate mortar to be grinded for 30 min. After that, the mixtures were packed into alumina crucibles by calcined in furnace at 800  C for 3 h, cooled to room temperaturealong with the furnace. The X-ray diffraction (XRD) pattern (D/Max-2200, Rigaku, Japan) on 40 kV and 40 mA with Cu Ka radiation was used to check the structure features ofthe KGd(MoO4)2:Sm3+ phosphors, the diffraction patterns were scanned at the range of 5–70 (2u). The morphology and microstructure of the samples were performed by FE-SEM (Hitachi S-4800). The excitation and emission spectra and decay curve were confirmed on a fluorescence spectrophotometer (FS5, Edinburgh) with a 150W Xe lamp as an excitation source. 3. Result and discussion 3.1. Phase identification Alkaline earth molybdates of the type AB(MoO4)2 (A = Li, Na, K; B = La, Gd, Lu, Y) crystal belong to scheelite structure. The crystal structure diagram of KGd(MoO2)4 was drawn using diamond 3.2

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software (Fig. 1). In the crystal structure of KGd(MoO2)4, Mo atom surrounded by four O atoms to form [MoO4] tetrahedra, Gd atom and K atom surround by eight O atoms to form [GdO8] and [KO8] polyhedra. The [MoO4] tetrahedra, [GdO8] and [KO8] polyhedra are connected with each other by corner-sharing O atoms. Fig. 2 shows the X-ray diffraction (XRD) patterns of the KGd (MoO4)2:Sm3+ phosphors at different concentrations of Sm3+ ions. All diffraction peaks were in good agreement with the standard JCPDS card No. 52–1694 (Fit triclinic system, space group P-1 and lattice parameters values of a = 11.1889 Å, b = 5.2844 Å, c = 6.9138 Å) and no other phases were discovered, it turned out that less doped Sm3+ ion was not change the host crystal structure and all samples were single-phased, and Jade-5.0 software were used to calculate the lattice parameters of KGd(MoO4)2:Sm3+ phosphors and shown in Table 1. It is obvious that the unit cell volume increased with the Sm3+ ion concentrations increased in the range of x = 0.02–0.10. The reason for this outcome can be attributed to the small ionic radii difference between Sm3+ ions (r = 0.964 Å) and Gd3+ ions (r = 0.938 Å), Sm3+ ions are slightly bigger than Gd3+ ions, this result showed that the activator Sm3+ ions were incorporated into the host lattice of KGd(MoO4)2 and Sm3+ ions effectively replace in the site of Gd3+ ions [7]. 3.2. SEM images and analysis SEM was used to study the surface microtopography and particle size of preparative phosphor powder. Fig. 3 shows SEM picture of two different amplification factors of KGd (MoO4)2:0.06Sm3+ phosphor (Fig. 3(a) is 2500 times, Fig. 3(b) is 10000 times). This product consists of microcrystalline grains with agglomeration under the high temperature solid state reaction. The obtained samples were composed of irregular particles with size in a range of 2–7 mm. 3.3. PL excitation and emission spectrum The photoluminescence (PL) excitation spectrum of the KGd (MoO4)2:Sm3+ phosphors while monitoring at 648 nm wavelength (which is Sm3+ ion emission wavelength) are shown in Fig. 4. It can be seen clearly that all the PL excitation spectrum have similar profile in addition to the intensity, and every excitation spectra consists of two parts, one is the weak broad band from 300 to 340 nm which is belong to the Mo-O charge transfer band (CTB).

Fig. 1. The crystal structure of KGd(MoO4)2. Note: Gd3+ cations are shown in yellow, Mo6+ cations are shown in bule, K+cations are shown in white, O2 anions are shown in red. And Sm3+ occupy the site of Gd3+. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.).

Fig. 2. X-ray diffraction patterns of KGd(MoO4)2:xSm3+ (x = 0.02, 0.04, 0.06, 0.08, 0.10) phosphors.

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Table 1 The calculated lattice parameters of KGd(MoO4)2:Sm3+ phosphors. Concentration of Sm3+ (x)

a (Å)

b (Å)

c (Å)

V (Å)

0.02 0.04 0.06 0.08 0.10

11.17072 11.17981 11.18434 11.19074 11.19666

5.27917 5.27933 5.28 5.28171 5.28279

6.90548 6.90593 6.90707 6.90875 6.9132

344.3 344.44 344.84 344.95 345.33

Fig. 3. SEM image of KGd(MoO4)2:0.06Sm3+ phosphor (a: Magnification of 2500 times;b: Magnification of 10000 times).

The existence of CTB in the excitation spectra indicates the occurrence of energy transfer process from MoO42 groups to Sm3+ ions. The other part consists of a series of narrow peaks from 340 to 500 nm which are assigned to the characteristic f–f transition from the low energy level 6H5/2 to higher energy levels of Sm3+ ion. These transitions locate at 347 nm occurs for 6H5/2 ! 4L15/2 transition, 364 nm for 6H5/2 ! 4L15/2 transition, 378 nm for 6H5/ 6 6 4 2 ! P7/2 transition, 406 nm for H5/2 ! F7/2 transition, 420 nm for 6 4 6 H5/2 ! P5/2 transition, 443 nm for H5/2 ! 4G9/2 + 4I15/2 transition,

468 nm for 6H5/2 ! 4I13/2 transition, 473 nm for 6H5/2 ! 4I11/2 transition and 482 nm for 6H5/2 ! 4I9/2 transition, respectively [16,19,25]. All energy level transitions locate at UV to blue light which show all synthetic samples can be excited by UV- or NUVLEDs and blue LEDs. However, it is obvious that the intensity of the f–f transition at 406 nm is higher than other transitions from Fig. 4, therefore, this transition can get the highest intensity of emission spectra, and also means Sm3+ doped KGd(MoO4)2 can be effectively excited by NUV-LEDs to get WLED. And then from Fig. 4, all excitation peak intensity connect with dopant concentration, every intensity increases when the dopant concentration increases untilthe intensity reaches its maximum at the concentration of 0.06, and then intensity decreases with concentration continues increase. The PL emission spectrum of the KGd(MoO4)2:Sm3+ phosphors while excited at 406 nm are shown in Fig. 5(a). The Sm3+ ion is excited to 4F7/2 level at 406 nm, however, due to nonradiative relaxation process cause 4F7/2 level relax to 4G5/2 level, all emission spectrum include mainly four peaks which are ascribed to 565 nm, 607 nm, 648 nm and 708 nm corresponding to the 4G5/2 ! 6H5/2, 4 G5/2 ! 6H7/2, 4G5/2 ! 6H9/2 and 4G5/2 ! 6H11/2 transitions, respectively, which belong to the typical transition of Sm3+ ion, such as Ba2CaZn2Si6O17:Sm3+ [26] and BaNb2O6:Sm3+ [27], and Fig. 5(a) shows the highest emission peak is 4G5/2 ! 6H9/2 transition locate at 648 nm, which belongs to the range of red. Among These transition bands of Sm3+ ions originate from 4G5/2 excited state to various lower energy states of 6HJ (J = 5/2, 7/2, 9/2 and 11/2), the 4 G5/2 ! 6H5/2 transition (DJ = 0) at 565 nm is a part of magnetic dipole (MD) transition which not affected by the crystalline field, the 4G5/2 ! 6H7/2 transition (DJ = 1) at 607 nm is a partly magnetic and partly forced electric dipole (ED) transition and the 4G5/ 6 2 ! H9/2 transition (DJ = 2) at 648 nm is attributed to ED transition which is more easily affected by the crystalline field [25–28]. Generally, the intensity ratio of electric-dipole to magnetic-dipole transitions is used to understand the symmetry of local environment of the trivalent rare earth ions. The ratio of ED to MD transitions is less than 1 indicate that the trivalent rare earth ions take up the symmetry site nature of the host lattice. In other words, the ratio of ED to MD transitions shows higher than 1 indicate that the trivalent rare earth ions occupy the asymmetry site nature of the host lattice [29]. In this present study, it can found that the ED transition higher than the MD transition, therefore, Sm3+ ions occupy asymmetry site in KGd(MoO4)2 lattice. Meanwhile, the intensity ratio of ED to MD with different activator concentration can be obtained and list in Table 2. Hence, the intensity ratio of ED to MD is around 4.477–4.546 when doping Sm3+ ion with different concentrations from 0.02 to 0.10, this result shows that the PL excitation spectrum have the same profile and don’t translocation with different Sm3+ ion concentrations, except intensity. To study the effect of activator concentration on the PL emission properties of the KGd(MoO4)2:Sm3+ phosphors, the PL emission intensity of 4G5/2 ! 6H9/2 transition of the KGd(MoO4)2:Sm3+ phosphors (Sm3+ ions mole concentration is 0.02, 0.04, 0.06, 0.08, 0.10) while excited at 406 nm is shown in Fig. 5(b). It is obvious to see from this inset that there is no change in the location of the emission band for all experimental doping concentrations. Nevertheless, the doping concentration of Sm3+ ions could influence the emission intensity, when the doping concentration of Sm3+ ions increased, the emission intensity also begins to increase and then the intensity reaches its maximum at 0.06 (critical concentration), but when the Sm3+ ion concentration continue to increase, the emission intensity begin to decrease because of concentration quenching effect. Thus, it is indicated that the optimum doping concentration of Sm3+ ion is 0.06.

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Fig. 4. The excitation spectrum of KGd(MoO4)2:xSm3+ (x = 0.02, 0.04, 0.06, 0.08, 0.10) phosphors at 648 nm monitor the wavelength.

3.4. Critical energy transfer distance and concentration quenching Compared with the PLE spectra of KGd(MoO4)2:Sm3+, it can be observed that the green emission at around 496 nm,yellow emission at around 587 nm and the red emission at around 628 nm in KGd(MoO4)2 pure host is miss and weaker when the excitation wavelength is 406 nm is given in Fig. 5(c). This phenomenon also confirms to energy transfer from the CTB to Sm3+. And then, taking into account the concentration quenching, it may be induced by cross relaxation processes due to proximity in Sm3+ ions, there is more possibility of enhancing the energy transfer within Sm3+ ions beyond through nonradiative process. The critical energy transfer distance (Rc) in KGd(MoO4)2:Sm3+ phosphors can be calculated by the following formula as suggested by Blasse [7,25]:  Rc ¼ 2

3V 4pxc Z

13

ð1Þ

where Rc is the critical distance between activator ions, V is the volume of the unit cell, Z is the number of cation in the unit cell and xc is the critical concentration of activator ion. For the KGd(MoO4)2:Sm3+ phosphors, V = 345.42 Å3, xc = 0.06 and Z = 2, thus Rc was calculated to be about 17.65 Å. Generally, the energy transfer has mainly three processes, which are exchange interaction, radiation re-absorption or multipolar interaction between rare earth ions. Exchange interaction occur when the Rc between the activator ions is less than 5 Å, and the second process of radiation re-absorption occur only when the emission and the excitation spectra of the sensitizer and the activator has a wide range of overlapping. In this case, the value of Rc is obviously more than 5 Å (about 17.65 Å), and so the second process is unlikely to occur, which shows that the energy transfer process of concentration quenching of KGd(MoO4)2:Sm3+ phosphors is mainly multipolar interaction. According to the Dexter’s theory [12,19], when the activator concentration is large enough, the PL emission intensity (I) and activated ion concentration (x) can suit to the following formula: logðI=xÞ ¼ C  ðu=3ÞlogðxÞ

ð2Þ

where x is the activator concentration, C is a constant and u = 6, 8 or 10 represent for dipole–dipole (d-d), dipole-quadrupole (d-q), quadrupole–quadrupole (q-q) interactions, respectively. The curve of log(I/x) contrast log(x) in KGd(MoO4)2:Sm3+ phosphors is shown on Fig. 6, with the curves, it can be calculated that the slope is

Fig. 5. (a) The emission spectrum of KGd(MoO4)2:xSm3+ (x = 0.02, 0.04, 0.06, 0.08, 0.10) phosphors excited at 406 nm. (b) The PL emission intensity of 4G5/2 ! 6H9/2 transition of KG(MoO4)2:Sm3+ phosphors at 406 nm. (c) The emission spectrum of KGd(MoO4)2 and KGd(MoO4)2:0.06Sm3+ phosphor excited at 406 nm.

1.59. Therefore, the u is 4.77 near to 6, this result shows that the concentration quenching mechanism of 4G5/2 level of KGd(MoO4)2: Sm3+ phosphor is d–d interaction. The energy level diagram of Sm3+ ion is shown in Fig. 7, when the low 6H5/2 level of Sm3+ ion was excited to high 4F7/2 level at 406 nm wavelength, because of between 4F7/2 level and 4G5/2 level have several energy levels and these energy levels had little energy differences which leads to occur non-radiative relaxation process between 4F7/2 level and 4G5/

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Table 2 The ratio of ED to MD transitions value of KGd(MoO4)2:Sm3+ phosphors as a function of Sm3+ ions concentration. Concentration of Sm3+ ion (mol)

4

G5/2 ! 6H5/2

0.02 0.04 0.06 0.08 0.10

160289.453 165234.484 210187.781 156853.938 154481.891

4

G5/2 ! 6H9/2

728614.188 739794.75 941237.438 705939.25 693775.438

ED/MD 4.546 4.477 4.478 4.500 4.490

2 level. According to Bungala Chinna Jamalaiah et al. [25], Amit K. Vishwakarmaetal [27]. and L Wang [29]. studied, the energy transfer process take placed through cross relaxation channels is ascribed to four processes: (4G5/2 + 6H5/2) ! (6F5/2 + 6F11/2), (4G5/ 6 6 6 4 6 6 6 4 2 + H5/2) ! ( F7/2 + F9/2), ( G5/2 + H5/2) ! ( F9/2 + F7/2) and ( G5/ 6 6 6 4 2 + H5/2) ! ( F11/2 + F5/2), responsible for depopulating the G5/2 level can be found as describe in Fig. 7.

3.5. The CIE chromaticity coordinates The Commission International del’Eclairage (CIE) is a good method for determining the exact emission color. Therefore, the CIE chromaticity coordinates (x, y) of the KGd(MoO4)2:Sm3+ phosphors were calculated from the PL emission spectra under 406 nm is shown in Table 3. It can be found nearly the same chromaticity coordinates (x, y) for all samples with different Sm3+ ion concentrations, this result consistent with the radio of MD to ED value, thus indicating the KGd(MoO4)2:Sm3+ phosphors have stable luminescent properties consistent with above. Fourthermore, the chromaticity diagram of the KGd(MoO4)2:0.06Sm3+ phosphor is shown in Fig. 8, the CIE chromaticity coordinate for KGd(MoO4)2:0.06Sm3+ phosphor is calculated to be (0.621,0.377) and is found nearly the same as other concentrations and all chromaticity coordinates are located at red area. Hence, the KGd (MoO4)2:Sm3+ phosphors are promising materials for application in the red light for NUV-based WLED. 3.6. Decay characteristics

Fig. 6. The Fit line of log(I/x) versus log(x) in 4G5/2 ! 6H9/2 transitions of Sm3+ doped KGd(MoO4)2 phosphors.

Fig. 9 shows the luminescence decay curves of 4G5/2 excited level of Sm3+ in KGd(MoO4)2:Sm3+ (The concentration of Sm3+is 0.02, 0.04, 0.06, 0.08, 0.10) phosphors which have been confirmed under 406 nm excitation and 648 nm emission (4G5/2 ! 6H9/2 transition). All the decay curves are well fitted to a double exponential function [28]: IðtÞ ¼ A1 expðt=t 1 Þ þ A2 expðt=t 2 Þ þ I0

ð3Þ

where I0 and I(t) are intensities at time 0 and t, A1 and A2 are the constants, t1 and t 2 are the decay time. Thus, the average lifetime can be get from double exponential fitting by this equation:

t avg ¼

A1 t 21 þ A2 t 22 A1 t 1 þ A2 t 2

ð4Þ

Fig. 7. Partial energy level diagram and cross relaxation channels of Sm3+ions.

Table 3 The CIE chromaticity coordinates of KGd(MoO4)2:Sm3+ phosphors. Concentration of Sm3+ ions (mol)

CIE chromaticity coordinates(x, y)

0.02 0.04 0.06 0.08 0.10

(0.618, 0.380) (0.619, 0.379) (0.621,0.377) (0.619, 0.378) (0.619, 0.379) Fig. 8. Chromaticity coordinates of the KGd(MoO4)2:0.06Sm3+ phosphors in the CIE 1993 chromaticity diagram.

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Fig. 9. Decay curves of KGd(MoO4)2:Sm3+ phosphors for different concentration of Sm3+ ions.

3.7. The quantum efficiency QE is an important parameter for phosphor, in order to accurately investigate the luminescent properties of KGd (MoO4)2:Sm3+ phosphors, which is defined as the ratio between the number of emitted photons (Iem) and the number of absorbed photons (Iabs), It can be expressed by the following formula [30,31]: QE ¼

Iem LS ¼ Iabs ER  ES

where LS is the intensity of luminescence emission, ER is the excitation light without the sample in the integrating sphere, and ES is the excitation light with the sample in the integrating sphere. The QE of the optimized KGd(MoO4)2:0.06Sm3+ phosphor was measured though the integrating sphere method. The sample was excited using 406 nm light produce by the Xenon Lamp and the scan range of 386–750 nm. Accordingly, the measurement result is shown in Fig. 10 and the QE value was determined to be 28.5%. Fig. 10. Excitation and emission spectra of KGd(MoO4)2:0.06Sm3+ and reference samples for QE measurement.

Based on equation, the average lifetime values calculated were 870.85 ms, 781 ms, 693.42 ms, 561.9 ms and 552.54 ms corresponding to 0.02, 0.04, 0.06, 0.08, 0.10 of Sm3+ ion concentrations are shown in Fig. 9, the decay curves conform to double exponential behavior is frequently observed, when the excitation energy is transferred from the donor [12,26]. In this study, this behavior indicates the energy transfer from MoO42 group to the Sm3+ ions. Furthermore, when Sm3+ ion concentration increased, both the energy transfer rate between Sm3+ to Sm3+ and the probability of energy transfer to quenching sites increase, therefore, the lifetime decreases with the increasing Sm3+ ion concentration. Generally, Sm3+-doped phosphor have a decay time due to a forbidden transition of Sm3+ ions according to spin selection rule, this transition has a very low probability and decay time is in the order of millisecond or submicrosecond [15]. Thus, the lifetime of the KGd(MoO4)2:Sm3+ phosphors is short enough for potential applications in lighting field.

4. Conclusions In summary, a series of KGd(MoO4)2:Sm3+ phosphors were successfully prepared by a high temperature solid state reaction method. The KGd(MoO4)2:Sm3+ phosphors have four emission peaks at 565 nm, 607 nm, 648 nm and 708 nm corresponding to the 4 G5/2 ! 6H5/2, 4G5/2 ! 6H7/2, 4G5/2 ! 6H9/2 and 4G5/2 ! 6H11/2 transitions of Sm3+ ions under 406 nm wavelength. The PL excitation spectrum show a series of excitation band range from 250 nm to 500 nm, and they can be effectively excited by UV (or NUV) chips for potential applications in WLED. From PL spectrum, the optimum dopant concentration of Sm3+ ion is 0.06 in KGd (MoO4)2 host lattice, thus the Rc is calculated to be 17.65 Å, and the concentration quenching mechanism of KGd(MoO4)2:Sm3+ phosphors determine electric dipole–dipole interaction. The color coordinates for KGd(MoO4)2:0.06Sm3+ phosphor is calculated to be (0.621, 0.377) in the red region. The decay curves are fitted to the double exponential function, and average lifetimes for the 4G5/2 excited level of Sm3+ in the KGd(MoO4)2 host lattice is in the submicrosecond. Finally, The QE value is determined to be 28.5%. And Hence, the KGd(MoO4)2:Sm3+ red phosphors can be a promising materials for WLED.

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