Synthesis, Luminescent Properties and White LED Fabrication of Sm 3+ Doped Lu 2 WMoO 9

: In this paper, Sm 3+ doped Lu 2 W 0.5 Mo 0.5 O 6 , Lu 2 WMoO 9 , and Lu 2 (W 0.5 Mo 0.5 O 4 ) 3 materials were synthesized by using a two-step solid-state reaction method. The synthesized materials were characterized by X-ray diffraction (XRD) patterns, ﬁeld emission scanning electronic micrograph (FE-SEM) pictures, photoluminescence (PL) excitation and emission spectra, and temperature-dependent emission intensities. Orange-reddish light could be observed from the phosphors under ultraviolet (UV) 365 nm light. The Sm 3+ doped Lu 2 WMoO 9 had enhanced PL intensities compared to the other two materials. The excitation, the energy transfer, the nonradiative relaxation, and the emission processes were illustrated by using schematic diagrams of Sm 3+ in Lu 2 MoWO 9 . The optimal Sm 3+ doping concentration was explored in the enhancing luminescence of Lu 2 WMoO 9 . By combing the Sm 3+ doped Lu 2 WMoO 9 to UV 365 nm chips, near white lighting emitting diode (W-LED) were obtained. The phosphor can be used in single phosphor-based UV W-LEDs.


Introduction
As a new generation light source, phosphor-based converted white-light emitting diodes (W-LEDs) have been researched and used due to their advantages in energy saving, high luminous efficiency, reliability, and environmental friendliness, etc. [1,2]. The commonly used commercial phosphor based W-LEDs are usually based on the combination of blue LED chips with yellow Y 3 Al 5 O 12 :Ce 3+ (YAG:Ce 3+ ) phosphors [3]. Due to the scarcity of red emissions, the W-LEDs have high correlated color temperature and other problems, such as low color-rendering index, low thermal quenching temperature, chromatic stabilities, narrow visible range, etc. [4,5]. Correspondingly, the combination of ultraviolet (UV) LED chips combined with tri-color RGB (red, green, blue) phosphors or blue LED chips combined with green and red phosphors have been proposed [6,7]. Therefore, the phosphors which have broad absorption band in the UV and/or blue wavelength band and red phosphors have been widely researched [8,9].
For the intense and broad charge transfer band (CTB) absorption in the UV wavelength band and excellent physical and chemical stability, molybdate and tungstate host phosphors have been widely studied [10,11]. The most widely investigated rare-earth ion is the Eu 3+ due to its characteristic red emissions from the 5 D 0 → 7 F 2 transition [12] or Eu 2+ [13].
As an alternative choice of Eu 3+ , new red emitters need to be explored, too. Sm 3+ is a good choice as an orange-red activator ion in luminescent materials [14]. The Sm 3+doped luminescent materials can be used in solid-state lighting devices [15,16]. The Sm 3+ characteristic emissions are 4 G 5/2 → 6 H 5/2,7/2,9/2,11/2 transitions. The yellow 4 G 5/2 → 6 H 5/2 transition is a magnetic dipole transition (MD), which is insensitive to the local environment. The 4 G 5/2 → 6 H 7/2 transition is an orange emission, which is a combined MD and electricdipole (ED) transition. While the red emission 4 G 5/2 → 6 H 9/2 , is an ED transition, which is greatly influenced by the local symmetry of the Sm 3+ ion [16]. The ED/MD transition intensity ratio is usually used to judge the local environment around the Sm 3+ ; the ED transition is stronger, the asymmetry property is greater, and vice versa.
For the broad UV band absorption of tungstates and molybdates, the energy transfer process can take place in the RE-doped tungstates and molybdates considering the energy transfer theory [17,18]. Sm 3+ , Eu 3+ , Dy 3+ , Ho 3+ , etc., doped Y 2 WO 6 and Lu 2 WO 6 have been well reported and researched [15,17,19,20]. Unlike usually used YAG:Ce 3+ Lu 3 Al 5 O 12 :Ce 3+ /CaAlSiN 3 :Eu 2+ phosphors [21,22], the CTB of WO 6 6− locates at about 300 nm and cannot be directly used in UV LED devices. As a choice, Mo 6+ can be added to shift the excitation band to a longer wavelength of tungstates as well as enhancing the luminescence of Eu 3+ [23][24][25]. Based on the above consideration, some Sm 3+ doped lutetium tungsten molybdenum oxides Lu 2 W 0.5 Mo 0.5 O 6 , Lu 2 W(Mo) 2 O 9 , and Lu 2 (W 0.5 Mo 0.5 O 4 ) 3 were synthesized. Enhancing luminescence of Sm 3+ and red-shifted excitation band compared Lu 2 W 0.5 Mo 0.5 O 6 and Lu 2 (W 0.5 Mo 0.5 O 4 ) 3 were obtained in Lu 2 WMoO 9 materials. The excitation, the energy transfer, and the emission processes in Lu 2 WMoO 9 were elucidated, and the optimal doping concentration of Sm 3+ in Lu 2 WMoO 9 was studied. W-LEDs were obtained by combining the Sm 3+ doped Lu 2 WMoO 9 to 365 nm UV chips. The experimental results suggest that the enhancing Sm 3+ doped Lu 2 WMoO 9 phosphors can be used in single-phosphor-based W-LEDs.

Materials and Methods
By using a two-step solid-state reaction method reported in reference [26] To explore the optimal Sm 3+ doping concentration in Lu 2 WMoO 9 phosphors, the Sm 3+ concentration (corresponding Lu 2 O 3 ) 0.5, 1, 2, 3, 5, and 7 mol% were selected to synthesis the phosphors.
The obtained materials were characterized by X-ray diffraction (XRD, Rigaku, Tokyo, Japan) patterns, field emission scanning electron microscope (FE-SEM, Zeiss, Jena, Gemany) images, and room temperature photoluminescence (PL, Thermo scientific, Waltham, USA) excitation and emission spectra. The data were recorded by the same apparatuses in reference [26]. The LED lamps were fabricated by coating the 3 mol.% Sm 3+ doped Lu 2 WMoO 9 phosphors onto the 365 nm LED chips. The fabrication procedure and the measurements are similar to those used in [26].  could be referred to the orthorhombic phase of Y 2 W 3 O 12 with the JCPDS No. 15-0447 [27]. Using different molar ratio of raw materials, the obtained phosphor crystalized in different crystalline phases, which will affect the luminescence greatly.

Crystalline and Morphology
Coatings 2021, 11, x FOR PEER REVIEW 3 of 9 reference data of Lu2Mo2O9 with JCPDS No. 28-0613. The diffraction peak was marked as an inverted triangle which became stronger as 50% percent of Mo 6+ was replaced by W 6+ . For the raw materials Lu2O3(Sm2O3):WO3:MoO3 = 1:1.5:1.5, the obtained XRD pattern could be referred to the orthorhombic phase of Y2W3O12 with the JCPDS No. 15-0447 [27]. Using different molar ratio of raw materials, the obtained phosphor crystalized in different crystalline phases, which will affect the luminescence greatly.   reference data of Lu2Mo2O9 with JCPDS No. 28-0613. The diffraction peak was marked as an inverted triangle which became stronger as 50% percent of Mo 6+ was replaced by W 6+ . For the raw materials Lu2O3(Sm2O3):WO3:MoO3 = 1:1.5:1.5, the obtained XRD pattern could be referred to the orthorhombic phase of Y2W3O12 with the JCPDS No. 15-0447 [27].
Using different molar ratio of raw materials, the obtained phosphor crystalized in different crystalline phases, which will affect the luminescence greatly.    Figure 3 presents the room temperature PL spectra of 2 mol.% Sm 3+ doped Lu 2 MoWO 9 phosphor. By monitoring the Sm 3+ 614 nm emission from 4 G 5/2 → 6 H 7/2 , the PL excitation spectrum is shown in the left part in Figure 3. The spectrum was composed of two components, which include a broad charge transfer band (CTB) and several sharp Sm 3+ 4f-4f peaks. The CTB was located in the wavelength range of 200-450 nm, with the strongest peak at about 368 nm, which was consistent with UV 365 nm chips. The CTB had two peaks located at 305 nm and 368 nm, which were ascribed to O 2− -W 6+ and O 2− -Mo 6+ CTBs, respectively. The sharp peaks located at 407 nm and 469 nm originated from the 6 H 5/2 ground state to the 4 F 7/2 , 4 I 13/2 excited states, respectively [28]. With the CTB 368 nm excitation, the PL emission spectrum is illustrated in the right part of Figure 3. There were four emission peaks at 567, 603 (614), 650 (660), and 712 nm, which could be ascribed to the Sm 3+ 4 G 5/2 to 6 H 5/2, 7/2, 9/2, 11/2 transitions, respectively. The orange-red emission of 4 G 5/2 → 6 H 7/2 was the strongest one. The ED transition 4 G 5/2 → 6 H 9/2 was stronger than the MD transition G 5/ → 6 H 5/2 , which indicated the asymmetrical nature of Sm 3+ in the Lu 2 MoWO 9 lattice. The broad and strong excitation band locates in the UV wavelength range, which means that the phosphors could be efficiently excited by the UV chips and can be used in UV-based LEDs.

PL Spectra
Lu2Mo0.5W0.5O6 (a,b), Lu2MoWO9 (c,d), and Lu2(Mo0.5W0.5O4)3 (e,f). Figure 3 presents the room temperature PL spectra of 2 mol.% Sm 3+ Lu2MoWO9 phosphor. By monitoring the Sm 3+ 614 nm emission from 4 G5/2 6 H7/2 excitation spectrum is shown in the left part in Figure 3. The spectrum was comp two components, which include a broad charge transfer band (CTB) and severa Sm 3+ 4f-4f peaks. The CTB was located in the wavelength range of 200-450 nm, w strongest peak at about 368 nm, which was consistent with UV 365 nm chips. T had two peaks located at 305 nm and 368 nm, which were ascribed to O 2− -W O 2− -Mo 6+ CTBs, respectively. The sharp peaks located at 407 nm and 469 nm ori from the 6 H5/2 ground state to the 4 F7/2, 4 I13/2 excited states, respectively [28]. With t 368 nm excitation, the PL emission spectrum is illustrated in the right part of F There were four emission peaks at 567, 603 (614), 650 (660), and 712 nm, which c ascribed to the Sm 3+ 4 G5/2 to 6 H5/2, 7/2, 9/2, 11/2 transitions, respectively. The orange-re sion of 4 G5/2 6 H7/2 was the strongest one. The ED transition 4 G5/2 6 H9/2 was strong the MD transition G5/ 6 H5/2, which indicated the asymmetrical nature of Sm 3 Lu2MoWO9 lattice. The broad and strong excitation band locates in the UV wav range, which means that the phosphors could be efficiently excited by the UV ch can be used in UV-based LEDs. To illustrate the excitation, the energy transfer (ET), the nonradiative rel (NR), and the emission processes in the Sm 3+ doped Lu2MoWO9, the schematic levels of Sm 3+ and the processes in Lu2MoWO9 phosphor were schematically ( Figure 4). The Lu2MoWO9 host lattice absorbs the UV light in the 250-420 nm length range due to the O 2--W 6+ , O 2--Mo 6+ , and O 2--Sm 3+ CTBs [29][30][31]. The absorp ergy was transferred to the higher excited states of Sm 3+ . Then the NR processes oc The energy was relaxed to the excited state of 4 G5/2, and the radiative electron tra from the 4 G5/2 state to 6 H5/2,7/2,9/2,11/2 states occurred, giving the orange-reddish emiss addition, the 6 H5/2 ground state of Sm 3+ could also absorb the excitation energy higher excited states. After the NR processes to the excited state of 4 G5/2, orangeemissions could be recorded for the 4 G5/2 to 6 H5/2,7/2,9/2,11/2 transitions. To illustrate the excitation, the energy transfer (ET), the nonradiative relaxation (NR), and the emission processes in the Sm 3+ doped Lu 2 MoWO 9 , the schematic energy levels of Sm 3+ and the processes in Lu 2 MoWO 9 phosphor were schematically plotted (Figure 4). The Lu 2 MoWO 9 host lattice absorbs the UV light in the 250-420 nm wavelength range due to the O 2--W 6+ , O 2--Mo 6+ , and O 2--Sm 3+ CTBs [29][30][31]. The absorption energy was transferred to the higher excited states of Sm 3+ . Then the NR processes occurred. The energy was relaxed to the excited state of 4 G 5/2 , and the radiative electron transitions from the 4 G 5/2 state to 6 H 5/2,7/2,9/2,11/2 states occurred, giving the orange-reddish emissions. In addition, the 6 H 5/2 ground state of Sm 3+ could also absorb the excitation energy to the higher excited states. After the NR processes to the excited state of 4 G 5/2 , orange-reddish emissions could be recorded for the 4 G 5/2 to 6 H 5/2,7/2,9/2,11/2 transitions.  The PL excitation (left part) and emission (right part) spectra of the three samples of Sm 3+ doped Lu2Mo0.5W0.5O6, Lu2MoWO9, and Lu2(Mo0.5W0.5O4)3 are illustrated in Figure 5. The Lu2MoWO9 sample presented the strongest excitation and emission intensities. The CTB band was located at about 368 nm, and the strongest emission was located at about 614 nm. Compared to those of Lu2MoWO9, the Lu2Mo0.5W0.5O6 illustrated weaker PL excitation and emission intensities, the excitation and emission intensities of Lu2MoWO9 were about 4.5 times of those of Lu2Mo0.5W0.5O6. The Sm 3+ doped Lu2(Mo0.5W0.5O4)3 presented the weakest CTB intensity and the absorption peak located at about 288 nm. On the one hand, in the Lu2Mo0.5W0.5O6 and Lu2MoWO9 phosphors, the CTB absorption intensities were much stronger than those of the 4f-4f excitation from Sm 3+ . On the other hand, the situation was the opposite. In the Lu2(Mo0.5W0.5O4)3 material, the intensity of the PL excitation from Sm 3+ 4f-4f was stronger than that of CTB. With 405 nm excitation, the Lu2(Mo0.5W0.5O4)3 presented the strongest emission at about 600 nm and the different splits of those of Lu2MoWO9 and Lu2Mo0.5W0.5O6, which illustrated that the Sm 3+ was located at different crystalline sites. For the Sm 3+ doped Lu2MoWO9 presents the strongest PL intensities, the PL excitation and emission spectra of Sm 3+ doping concentration of Lu2(1-x)Sm2xMoWO9 were explored. Figure 6 shows the excitation spectra of Lu2(1−x)Sm2xMoWO9 by monitoring at Sm 3+ 614 nm emission. With the increase in Sm 3+ concentration, the intensities of the CTB firstly increased, achieved the maximum with the x = 0.03, and then decreased when the x values increased further. For clarity, the x value-dependent CTB intensities are shown in On the one hand, in the Lu 2 Mo 0.5 W 0.5 O 6 and Lu 2 MoWO 9 phosphors, the CTB absorption intensities were much stronger than those of the 4f-4f excitation from Sm 3+ . On the other hand, the situation was the opposite. In the Lu 2 (Mo 0.5 W 0.5 O 4 ) 3 material, the intensity of the PL excitation from Sm 3+ 4f-4f was stronger than that of CTB. With 405 nm excitation, the Lu 2 (Mo 0.5 W 0.5 O 4 ) 3 presented the strongest emission at about 600 nm and the different splits of those of Lu 2 MoWO 9 and Lu 2 Mo 0.5 W 0.5 O 6 , which illustrated that the Sm 3+ was located at different crystalline sites.  The PL excitation (left part) and emission (right part) spectra of the three samples of Sm 3+ doped Lu2Mo0.5W0.5O6, Lu2MoWO9, and Lu2(Mo0.5W0.5O4)3 are illustrated in Figure 5. The Lu2MoWO9 sample presented the strongest excitation and emission intensities. The CTB band was located at about 368 nm, and the strongest emission was located at about 614 nm. Compared to those of Lu2MoWO9, the Lu2Mo0.5W0.5O6 illustrated weaker PL excitation and emission intensities, the excitation and emission intensities of Lu2MoWO9 were about 4.5 times of those of Lu2Mo0.5W0.5O6. The Sm 3+ doped Lu2(Mo0.5W0.5O4)3 presented the weakest CTB intensity and the absorption peak located at about 288 nm. On the one hand, in the Lu2Mo0.5W0.5O6 and Lu2MoWO9 phosphors, the CTB absorption intensities were much stronger than those of the 4f-4f excitation from Sm 3+ . On the other hand, the situation was the opposite. In the Lu2(Mo0.5W0.5O4)3 material, the intensity of the PL excitation from Sm 3+ 4f-4f was stronger than that of CTB. With 405 nm excitation, the Lu2(Mo0.5W0.5O4)3 presented the strongest emission at about 600 nm and the different splits of those of Lu2MoWO9 and Lu2Mo0.5W0.5O6, which illustrated that the Sm 3+ was located at different crystalline sites. For the Sm 3+ doped Lu2MoWO9 presents the strongest PL intensities, the PL excitation and emission spectra of Sm 3+ doping concentration of Lu2(1-x)Sm2xMoWO9 were explored. Figure 6 shows the excitation spectra of Lu2(1−x)Sm2xMoWO9 by monitoring at Sm 3+ 614 nm emission. With the increase in Sm 3+ concentration, the intensities of the CTB firstly increased, achieved the maximum with the x = 0.03, and then decreased when the x values increased further. For clarity, the x value-dependent CTB intensities are shown in For the Sm 3+ doped Lu 2 MoWO 9 presents the strongest PL intensities, the PL excitation and emission spectra of Sm 3+ doping concentration of Lu 2(1-x) Sm 2x MoWO 9 were explored. Figure 6 shows the excitation spectra of Lu 2(1−x) Sm 2x MoWO 9 by monitoring at Sm 3+ 614 nm emission. With the increase in Sm 3+ concentration, the intensities of the CTB firstly increased, achieved the maximum with the x = 0.03, and then decreased when the x values increased further. For clarity, the x value-dependent CTB intensities are shown in the inset ( Figure 6). The results suggest that the optimal x value was 0.03 for CTB excitation.

PL Spectra
Coatings 2021, 11, x FOR PEER REVIEW 6 of 9 the inset ( Figure 6). The results suggest that the optimal x value was 0.03 for CTB excitation. The corresponding emission spectra of Lu2(1−x)Sm2xMoWO9 are shown in Figure 7. With UV 368 nm excitation, the characteristic emissions of Sm 3+ were recorded. With the x values increasing, the PL emission intensity increased, reached the maximum with x equals 0.03, and decreased when the x value increased further. For the CTB excitation, the Sm 3+ optimal doping was 0.03.

W-LED Fabrication and Characterization
For the CTB locates at UV wavelength range, and orange-red emission can be observed under UV 365 nm light, the Sm 3+ doped Lu2MoWO9 phosphor was fabricated to UV LED by combining 365 nm chips. Figure 8 shows a representative PL emission spectrum of packaged LED with a 50 mA current pumping. The spectrum suggests that the Sm 3+ doped Lu2MoWO9 phosphor could be efficiently excited by 365 nm light from the chip and gave orange-reddish light. Combined with the chip light, the fabricated LED gave near-white light, which is shown in the inset of Figure 8a. The corresponding rec- The corresponding emission spectra of Lu 2(1−x) Sm 2x MoWO 9 are shown in Figure 7. With UV 368 nm excitation, the characteristic emissions of Sm 3+ were recorded. With the x values increasing, the PL emission intensity increased, reached the maximum with x equals 0.03, and decreased when the x value increased further. For the CTB excitation, the Sm 3+ optimal doping was 0.03.
Coatings 2021, 11, x FOR PEER REVIEW 6 of 9 the inset ( Figure 6). The results suggest that the optimal x value was 0.03 for CTB excitation.

W-LED Fabrication and Characterization
For the CTB locates at UV wavelength range, and orange-red emission can be observed under UV 365 nm light, the Sm 3+ doped Lu2MoWO9 phosphor was fabricated to UV LED by combining 365 nm chips. Figure 8 shows a representative PL emission spectrum of packaged LED with a 50 mA current pumping. The spectrum suggests that the Sm 3+ doped Lu2MoWO9 phosphor could be efficiently excited by 365 nm light from the chip and gave orange-reddish light. Combined with the chip light, the fabricated LED gave near-white light, which is shown in the inset of Figure 8a. The corresponding rec-

W-LED Fabrication and Characterization
For the CTB locates at UV wavelength range, and orange-red emission can be observed under UV 365 nm light, the Sm 3+ doped Lu 2 MoWO 9 phosphor was fabricated to UV LED by combining 365 nm chips. Figure 8 shows a representative PL emission spectrum of packaged LED with a 50 mA current pumping. The spectrum suggests that the Sm 3+ doped Lu 2 MoWO 9 phosphor could be efficiently excited by 365 nm light from the chip and gave orange-reddish light. Combined with the chip light, the fabricated LED gave near-white light, which is shown in the inset of Figure 8a. The corresponding recorded Commission International del'Eclairage (CIE) diagram is presented in the insets as Figure 8b, and the chromaticity coordinates were 0.453 and 0.346, which deviated slightly from the white standard point, 0.333 and 0.333. The chromaticity coordinates were located in the white area and near to red area in the diagram. The measured color temperature was 2260 K, and the color purity was 0.397. The PL emission spectrum of the phosphor obtained from LED was consistent with the spectrum recorded under the fluorescence spectrophotometer. In addition, the temperature-dependent emission intensities were measured and added as an inset (Figure 8c). With the temperature increasing from 50 • C to 250 • C, the emission intensity decreased continuously. At 150 • C, the emission intensity maintained 67% intensity of 50 • C. The data and results suggest that the obtained Sm 3+ doped Lu 2 MoWO 9 phosphor has potential applications as a single phosphor in UV chip-based phosphor-converted W-LEDs.
orded Commission International del'Eclairage (CIE) diagram is presented in the insets as Figure 8b, and the chromaticity coordinates were 0.453 and 0.346, which deviated slightly from the white standard point, 0.333 and 0.333. The chromaticity coordinates were located in the white area and near to red area in the diagram. The measured color temperature was 2260 K, and the color purity was 0.397. The PL emission spectrum of the phosphor obtained from LED was consistent with the spectrum recorded under the fluorescence spectrophotometer. In addition, the temperature-dependent emission intensities were measured and added as an inset (Figure 8c). With the temperature increasing from 50 °C to 250 °C , the emission intensity decreased continuously. At 150 °C , the emission intensity maintained 67% intensity of 50 °C . The data and results suggest that the obtained Sm 3+ doped Lu2MoWO9 phosphor has potential applications as a single phosphor in UV chip-based phosphor-converted W-LEDs.

Conclusions
Through a solid-state reaction method, Sm 3+ doped Lu2Mo0.5W0.5O6, Lu2MoWO9, and Lu2(Mo0.5W0.5O4)3 phosphors were obtained. The Sm 3+ doped Lu2MoWO9 illustrated the strongest PL intensities in the three samples. The host CTB absorption located at about 370 nm was much stronger than the 4f-4f excitations of Sm 3+ in the Lu2Mo0.5W0.5O6 and Lu2MoWO9. The ET process played an important role in the Sm 3+ emissions. The optimal doping concentration of Sm 3+ was 0.03 for CTB excitation in Lu2(1−x)Sm2xMoWO9 phosphors. The temperature-dependent PL emission intensity suggested that the intensity decreased continuously with the temperature increasing. At 150 °C , the intensity was maintained at 67% of that at 50 °C . By combining 365 nm chips with Sm 3+ doped Lu2MoWO9 phosphors, W-LEDs could be obtained. The results suggest that the obtained phosphors could be used in single phosphor-based UV W-LEDs.
Author Contributions: Z.C. and H.X. contributed to the paper equally. Conceptualization, Z.C. and H.X.; methodology, M.Z. and X.C.; formal analysis, Z.C. and H.X.; investigation, C.C.; data curation, Z.C. and H.X.; writing-original draft preparation, M.J. and Y.L.; writing-review and editing, C.C.; funding acquisition, A.X. and C.C. All authors have read and agreed to the published version of the manuscript.

Conclusions
Through a solid-state reaction method, Sm 3+ doped Lu 2 Mo 0.5 W 0.5 O 6 , Lu 2 MoWO 9 , and Lu 2 (Mo 0.5 W 0.5 O 4 ) 3 phosphors were obtained. The Sm 3+ doped Lu 2 MoWO 9 illustrated the strongest PL intensities in the three samples. The host CTB absorption located at about 370 nm was much stronger than the 4f-4f excitations of Sm 3+ in the Lu 2 Mo 0.5 W 0.5 O 6 and Lu 2 MoWO 9 . The ET process played an important role in the Sm 3+ emissions. The optimal doping concentration of Sm 3+ was 0.03 for CTB excitation in Lu 2(1−x) Sm 2x MoWO 9 phosphors. The temperature-dependent PL emission intensity suggested that the intensity decreased continuously with the temperature increasing. At 150 • C, the intensity was maintained at 67% of that at 50 • C. By combining 365 nm chips with Sm 3+ doped Lu 2 MoWO 9 phosphors, W-LEDs could be obtained. The results suggest that the obtained phosphors could be used in single phosphor-based UV W-LEDs.