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Abstract
The realization of high front light emission in laser lighting under transmissive modes is heavily constrained by low thermal stability and light extraction efficiency of color converter materials. Therefore, it is necessary to improve the heat dissipation capacity and light utilization efficiency of the color converter through appropriate microstructural adjustments. In this study, what we believe to be a novel laminated structure consisting of Al2O3 and YAG:Ce was designed and fabricated for transmissive laser lighting. Through this design, it was possible to change the phosphor emission angle, overcoming the limitations of total internal reflection and enabling maximal emission of yellow phosphor from the ceramic surface. This laminated structure enhanced the front light emission efficiency by 24.4% compared to composite ceramic phosphor. In addition, the thermal conduction area between the phosphor layer and the heat dissipation layer have been effectively enhanced. Ultimately, under a high-power density of 47.6 W/mm2, all ceramics showed no luminous saturation threshold. A high-brightness front light with a luminous flux of 651 lm, a luminous efficiency of 144 lm/W, a correlated color temperature of 6419 K and the operating temperature as low as 84.9 °C was obtained. These results suggest that laminated structural Al2O3/YAG:Ce composite ceramic is a promising candidate for transmissive mode laser lighting.
© 2023 Optica Publishing Group under the terms of the Optica Open Access Publishing Agreement
1. Introduction
At present, laser-driven lighting technology has experienced rapid development, resulting in significant advantages including high brightness, low beam divergence, and small volume [1–4]. It is applied in high brightness fields such as automotive headlights, digital cinemas, stage lighting, and airport lighting [5–10]. The phosphor, as the core of light-emitting devices, may gather a large amount of heat generated in the light conversion process due to the high output power of laser diodes (LD) [11–15]. Considering the limited thermal conductivity of traditional encapsulation materials such as silica gel, organic resin, and glass, which typically range from 0.1 to 1.4 W m-1 K-1, the poor heat resistance makes them unsuitable under the excitation of LD with high power density over 10 W/mm2 [16–20].
Ceramic phosphor (CP) has emerged as a promising candidate for high-power LD lighting due to their favorable thermal conductivity properties [21–28]. Besides, the thermal conductivity and luminous efficiency (LE) could be further improved through addition of the secondary phase, such as Y2O3 (∼14 W m-1 K-1), MgAl2O3 (∼20 W m-1 K-1), Al2O3 (32-35 W m-1 K-1), MgO (47.2-53.5 W m-1 K-1), and AlN (320 W m-1 K-1) [29–35]. Specifically, Al2O3-YAG:Ce composite ceramic phosphor (CCP) has been widely studied due to the high thermal conductivity of Al2O3 and favorable refractive index matching between Al2O3 and YAG:Ce [31]. Lheureux’s group prepared Al2O3-YAG:Ce CCP with high thermal conductivity using spark plasma sintering method. Under the same output power excitation, the heat accumulation decreased by 47.8% compared to YAG:Ce CP [36]. Xie’s group designed a thermally self-managed Al2O3-YAG:Ce CCP that Al2O3 was served as the scattering center. When the content of Al2O3 was 24 wt.%, the LE of CCP was improved by 27.3% compared to that of Al2O3-free YAG:Ce ceramics [37]. However, with an increase content for the secondary phase, there is an inevitable decrease in the concentration of Ce3+ ion and it leads to a decreasing conversion efficiency. Therefore, it is necessary that the appropriate microstructural adjustments of luminous materials can not only increase the content of the Al2O3 phase, but also improve the LE.
As is well known, the mainstream encapsulation methods for laser lighting mainly include reflective mode and transmissive mode. In the transmissive mode, there is a consistent transport route between the blue laser and the yellow phosphor, which is beneficial to beam reshaping and encapsulation simplification [38–41]. Reilly’s group designed compact laser emitters using YAG: Ce single crystals and simplified the design and encapsulation of the devices through transmissive mode [42]. Zhao’s group devised a high-performance Al2O3-YAG:Ce CCP [43]. By encapsulating with transmissive mode, a luminous flux (LF) value of 639 lm was achieved, and it was shown that the thickness of the ceramic affected the probability of leakage for Ce3+ ion converted yellow light from the edge of the ceramic, finally affected the LE. Nevertheless, the relatively high refractive index for most luminous materials, such as n = 1.83 for YAG, a portion of the light was limited within the material by total internal reflection (TIR) effect (n = 1.0 for air), or existed a leakage from the sides or boundaries of the emitter [43]. This phenomenon weakened the LE of front light emission and further complicated the optical design in the encapsulation process. Therefore, a new structural design with high content secondary phase for CP is crucial to control the scattering degree of light beam and solve the internal total reflection effect of the interface, and these would ensure a high LE of the front light for transmissive laser lighting.
In this paper, a laminated structural Al2O3/YAG:Ce CCP consisting of alternate layers of Al2O3 and YAG:Ce was designed and fabricated by the solid-phase sintering method. Since the refractive index of the YAG:Ce layer was higher than that of the Al2O3 layer, the photon would be limited to oscillate propagation in the YAG:Ce layer, and this formed light waveguide structure, would optimize the optical path of the photon and improve the LE of ceramics. In addition, the heat generated from the YAG:Ce layer can also be quickly transferred to the Al2O3 layer, and this may effectively reduce thermal quenching caused by heat accumulation. Ultimately, a high-brightness front light was obtained under the excitation power density of 47.6 W/mm2, including a LF of 651 lm, a LE of 144 lm/W, a CCT of 6419 K, and the operating temperature was as low as 84.9 °C. These results show that Al2O3/YAG:Ce CCP is a promising candidate material for high power laser lighting.
2. Experimental method
The Al2O3/YAG:Ce CCP was fabricated by a high temperature vacuum solid state reaction method. The main raw materials included commercial Y2O3 (Alfa Aesar, Ward Hill, America, 99.99%), α-Al2O3 (Alfa Aesar, Ward Hill, America, 99.99%) and CeO2 (Alfa Aesar, Ward Hill, America, 99.99%). Firstly, the concentration of Ce3+ in YAG:Ce for the designed laminated Al2O3/YAG:Ce ceramics was set to 0.05 wt.%, 0.10 wt.%. After stoichiometric weighing, the raw materials were mixed in a rotation speed of 200 rpm for 12 h with organic polyethyleneimine (PEI) as dispersant and Al2O3 balls as grinding medium. After drying at 55 °C for 10 h, the dried powder was crushed and screened three times from 100 mesh, and dried in a muffle furnace at 800 °C for 6 h. The configured YAG:Ce precursor powder and α-Al2O3 were alternately placed in a grinding tool for medium dry pressing at 0.2 g each for a total of 20 layers, followed by cold isostatic pressing at 200 MPa for 200 s. Finally, the samples were sintered in a vacuum at 1740 °C for 8 h. Annealing in air at 1450 °C for 10 h was used to remove oxygen vacancies and internal stresses in ceramics. The CCP was sliced along the axial direction and finally cut into 10 × 3× (0.4∼1.0) mm ceramic pieces. The detailed manufacturing process of the ceramics is shown in Fig. 1. Sample nomenclature for different thicknesses and concentrations is given in Table 1. What’s more, the comparison group of CCP for this experiment, also prepared by the solid-phase sintering method. The final prepared CCP with a mass ratio of Al2O3 to YAG:Ce of 1:1, a thickness of 0.4 mm and a size of φ = 16 mm. The detailed preparation process can be found in Ref. [38].
Table 1. Nomenclature for ceramic samples with different thicknesses and concentrations
Morphologies of all samples were characterized by scanning electron microscopy (SEM, JSM-6510, JEOL, Tokyo, Japan). Photoluminescence (PL) and photoluminescence excitation (PLE) were recorded using a phosphor spectrophotometer (OmniFluo 900, Beijing, China). Temperature-dependent emission spectra were recorded using a configured temperature control system, with a 450W xenon lamp serving as the excitation source. The laser data of all samples with different power densities, including LF, CCT and CRI have been tested by spectrophotometer and integrating sphere (HAS-2000, Hangzhou, China). The input power density of LD was calculated by dividing the input power of LD by the area of the laser-irradiated spot. A fiber coupled blue LD with maximum output power of 4.54 W (4 A) and the NA = 0.22 was used. The core diameter was 200 microns. The area of laser-irradiated spot can be obtained from the divergence angle of the laser a (NA = n sin a, where NA was the numerical aperture, n was the refractive index of the fiber core diameter) and the distance of the laser irradiated on the ceramic. Therefore, the laser-irradiated spot was approximately an area of 0.0985 mm2 circular with diameter of 0.314 mm at a distance 0.1 mm. The temperature distribution of the ceramic surfaces was measured using an infrared camera (Fotric 225s, Fotric, America). A heat-conduct coefficient measurement device was used to test the thermal conductivity (Hotdisk 2500S, Goteborg, Sweden).
3. Results and discussion
Figure 2(a) provides the schematic diagram of TIR. According to the formula of TIR Eq:
where θc is the angle of incidence, n1 is the refractive index of the air (1), and n2 is the refractive index of the YAG:Ce ceramic (1.83) [44,45]. When θc surpasses 33 °, the incident light within the YAG:Ce ceramic undergoes TIR, and thus is confined to the inside of the ceramic or exits from the side of the ceramic. Figure 2(b) depicts the schematic diagram of the incident light entering a CCP. In composite ceramics, the presence of the secondary phase Al2O3 enabled the change of light propagation paths within the ceramic, thereby increasing the probability of Ce3+ ions absorbing blue light. However, due to the omnidirectional nature of phosphor emission, a significant amount of phosphor is trapped inside the ceramic due to TIR [43,46]. Additionally, a portion of yellow phosphor may escape from the ceramic edges, which ultimately results in reduced luminous efficiency. Therefore, the adoption of a stratified design allows for the alteration of the emission angle of phosphor, breaking the constraints imposed by TIR and enabling maximal emission of yellow phosphor from the ceramic surface. Furthermore, this structure could also be used to control light scattering, effectively limiting light within each layer. This limitation minimized light scattering and promoted beam convergence, thereby achieving forward emission of the beam. The specific optical path propagation model diagram is shown in Fig. 2(c).
Fig. 2. Schematic diagram of the internal optical path of the laminated structural Al2O3/YAG: Ce CCP. Light is incident on (a) TIR simulation diagram and (b) composite ceramics phosphor light path diagram, (c) Al2O3/YAG:Ce CCP light path diagram.
Figure 3(a) depicts the photographs of all the prepared laminated structural Al2O3/YAG:Ce CCPs. The words ‘YAG:Ce/Al2O3’ on the paper are prominently visible, with their clarity diminishes as the thickness increases. An optical transmissive micrograph is shown in Fig. 3(b), which shows that the Al2O3/YAG:Ce sample has a laminated structural distribution, with each layer having a thickness of approximately 200 µm. From the SEM of the ceramic interface of the laminated configuration structure in Fig. 3(c), it is composed of alternating structures including dark regions of Al2O3 and light regions of YAG:Ce. The limitation of the fabrication process contributed to the inhomogeneous laminated structural Al2O3/YAG:Ce CCP. However, the close combination facilitates the heat transfer from the YAG:Ce layer to the Al2O3 layer, shown in Fig. 3(d). SEM images of the interface show that the interfacial connections are relatively tight and strong. Notably, the grain size of YAG:Ce ranged from 5 µm to 13 µm, while the grain size of Al2O3 was significantly larger than that of YAG:Ce, forming a continuous grain boundary phase. Furthermore, there were a few pores in the CCP owing to different sintering temperatures for YAG:Ce and Al2O3. The presence of appropriate pores inside the ceramic could act as the scattering centers to improve the scattering of fluorescence inside the ceramic and thus enhance the uniformity of lighting [47]. All the above results suggested that the laminated structural Al2O3/YAG:Ce CCP could be synthesized directly by a simple solid-state reaction using raw materials such as Y2O3, Al2O3 and CeO2.
Fig. 3. (a) Images of Al2O3/YAG:Ce ceramics in daylight. (b) Optical transmissive micrographs. (c),(d) SEM images of CP10.04 sample and Al2O3/YAG:Ce at the interface.
The PLE (λem = 530 nm) and PL (λex = 460 nm) spectra for traditional and laminated ceramics structure are shown in Fig. 4(a, b). The concentration of Ce3+ ions in the CCP is 0.10 wt.%. For ceramics with distinct structural compositions, Fig. 4(a) demonstrates a lack of noticeable alterations in both the contour and placement of the excitation peaks. The PLE spectra exhibited a diminished excitation band at 340 nm and an intensified excitation band at 460 nm, which were ascribed to the Ce3+ excitation transitions at 4f-5d2 and 4f-5d1, respectively [48]. The emission spectra of ceramics with different structures of the same thickness are presented in Fig. 4(b), revealing the characteristic of Ce3+ 5d→4f broadband emission. The transformation process of PLE and PL could be readily observed from the simplified energy level diagram depicted in Fig. 4(c). It is noteworthy that the design of the laminated controlled the light scattering along the optical path, resulting in a higher excitation intensity and emission intensity in the laminated structural ceramics compared to the YAG:Ce-Al2O3 CCP.
Fig. 4. (a) PLE and (b) PL spectra of CP10.04 ceramics and YAG:Ce-Al2O3(460 nm excitation), (c) simplified energy level diagram.
Considering that the laminated structural ceramic is used for laser lighting, it may reach an operating temperature of approximately 150 °C [49]. To assess the high-power lighting capabilities of the fabricated laminated ceramics, the temperature-dependent PL spectra of CP10.04 and YAG:Ce-Al2O3 CCP at 460 nm excitation in the temperature range from 25 °C to 200 °C are shown in Fig. 5(a∼d). The PL intensity of CP10.04 and YAG:Ce-Al2O3 CCP exhibited a gradual decrease as the temperature increased. To visually observe the changes in emission intensity and peak wavelength, it is illustrated in Fig. 5(e). As the temperature increased from 25 °C to 200 °C, the peak wavelength of CP10.04 was red-shifted from 530 nm to 536 nm. The red-shift with increasing temperature, which could be attributed to thermal quenching, i.e., non-radiative processes within the Stokes shift. [50]. Figure 5(f) is the corresponding heat flow diagram. Heat generated by YAG:Ce layers could be quickly transferred to the adjacent Al2O3 layers and reduce heat accumulation of YAG:Ce layers. Then, the heat was transferred along the Al2O3 layers to the air. Thermal conductivity measured for laminated Al2O3/YAG:Ce CCP was 16.6 W m-1 K-1, and that for YAG:Ce- Al2O3 CCP was 13.45 W m-1 K-1, as shown in the inset table within Fig. 5(c). Due to the better thermal conductivity of CP10, and a layered design, the heat dissipation area in the light emitting area was further enhanced, which ultimately improves the thermal stability of the ceramic. The fact that the PL intensity at 150 °C remained at 92.45% of the intensity at room temperature demonstrated the outstanding thermal stability of the laminated structural Al2O3/YAG:Ce CCP.
Fig. 5. (a) and (b) CP10.04, (c) and (d) temperature-dependent PL spectra of YAG:Ce-Al2O3 CCP in the temperature range RT 250 °C under 460 nm excitation, (e) normalized temperature-dependent PL intensity and coordination diagram of the peak wavelength (f) the model of laminated Al2O3/YAG:Ce CCP corresponding heat flow diagram (thermal conductivity of CP10 and YAG:Ce-Al2O3 CCP are summarized in the interpolation table of the picture).
For detailed analysis of photo luminous properties, a white LD coupling a 455 nm laser emission source to a prepared CCP was constructed by transmissive mode. Figure 6(a) shows the optical structures of the main components of our experiments: fiber-coupled blue LD, copper plate (φ = 16 mm), Al2O3/YAG:Ce CCP. During the experiments, we obtained a high brightness light source by placing the sample directly above the fiber terminal for excitation. The incident power density of the Al2O3/YAG:Ce CCP was as high as 47.6 W/mm2. Figure 6(b) shows the photograph of the sample under blue light excitation. It was worth noting that the lateral beam of the ceramic was constrained by the copper plate, thereby ensuring the accuracy of our measurement of the frontal light emitted from the Al2O3/YAG:Ce CCP. Also, encapsulation with copper plates provides good heat dissipation from the ceramic. The optical performance of composite ceramics phosphor under the blue laser excitation was evaluated in a transmissive configuration, as illustrated in Fig. 6(c).
Fig. 6. Physical diagram (a) and lighting diagram (b) of LD lighting device in CP package, (c) simulation diagram of the measurement device for laser-driven lighting in a transmissive configuration.
The electroluminescence (EL) spectrum of Al2O3/YAG:Ce CCP under low power density laser excitation of 20.1 W/mm2 is shown in Fig. 7(a). A narrow band emission of 445∼465 nm and a broad emission band of 490∼750 nm were formed due to the excited radiation from LD and the 5d-4f transition of Ce3+ ions, respectively. The thickness of the laminated ceramics exhibited a significant effect on the spectral characteristics. Specifically, in Al2O3/YAG:Ce laminated structural ceramics featuring an identical Ce3+ concentration, the remaining blue light diminished progressively, and the lighting color gradually shifted from cool white to warm white with the increase in ceramic thickness from 0.4 mm to 1 mm, as illustrated in Fig. 7(a). In Fig. 7(b, c), at the same Ce3+ concentration, the CCT decreased with the increase of thickness from 24617 K to 5685 K for 0.05 wt.%, and from 6419 K to 4793 K for 0.10 wt.%, respectively. This phenomenon can be primarily attributed to the augmented ceramic thickness, which leads to an increase in the absolute content of Ce3+ ions [13]. Simultaneously, the frequency of blue light oscillation within the phosphor layer and the propagation distance of blue light in the ceramic are also enhanced, thereby improving the absorption of blue light by the phosphor layer. Therefore, the narrow-band emission of 445 to 465 nm decreased continuously with the increase of ceramic thickness, and the CIE moved to the yellow light region. Fortunately, the color coordinates of all the samples were distributed around the Planckian curve.
Fig. 7. (a) EL spectrum of Al2O3/YAG:Ce CCP under laser irradiation (power =2 W, power density =20.1 W/mm2). The insets are the light emission of samples under daylight. (b), (c) Color coordinates of the samples in the standard of CIE. The insets are specific the parameters of color coordinate and CCT.
The front light fluxes of the samples excited at different laser power densities are shown in Fig. 8(a). It could be seen that the LF increased linearly with increasing power density (0∼47.6 W/mm2) and no luminous saturation occurred in Al2O3/YAG:Ce CCP. As is widely recognized, luminous saturation is a common phenomenon in laser irradiation [51–53]. In our work, the concentration of Ce3+ in the sample was relatively low (0.10 at. %, 0.05 at. %), and low Ce3+ content had a positive effect on both strength quenching and thermal quenching [54]. Notably, the LF exhibited mostly positive correlation with the increase in thickness of the Al2O3/YAG:Ce CCP at the same concentration. Additionally, the LF emitted by all specimens significantly surpassed that of the YAG:Ce-Al2O3 CCP, a result that remained in alignment with our preceding discourse based on the schematic representation of incident light presented in Fig. 2. Nevertheless, the light flux of the CP10.10 specimen was observed to be lower than that of samples at the same concentration. This could potentially be attributed to a reduction in transparency resulting from the increased ceramic thickness, resulting in excessive scattering centers within the material, phosphor being lost inside the material, as depicted in Fig. 3. It was evident that all the samples exhibited high LE, primarily attributed to the laminated structural design. This structure enabled TIR of a portion of the blue laser within the YAG:Ce layer, effectively constrained beam divergence, optimized light scattering, and enhanced the absorption of blue light by the phosphor layer. All at once, it is possible to change the phosphor emission angle, overcoming the limitations of TIR and enabling maximal emission of yellow phosphor from the ceramic surface. In general, the LF of the CP10.04 can reach up to 675.8 lm, while showing a highest LE of 148.9 lm/W, which is much larger than the LE of YAG:Ce-Al2O3 CCP. The comparison to other reported works has been listed in Supplement 1, Table S1. Its luminous efficacy is extraordinarily stable at high power density, meeting the technical requirements of automotive headlights and flashlight lighting.
To further investigate the luminous priorities of Al2O3/YAG:Ce CCP, the changes of the associated CCT and the CRI of the ceramics with the increase of power density are shown in Fig. 9. It is evident that, except for sample CP05.04, which exhibited a relatively significant variation in color temperature and color rendering index, resulting in color coordinate drift, the remaining samples demonstrated a narrow range of variation in CCT and CRI. These samples exhibited excellent color stability. With an increase in thickness from 0.4 to 1.0 mm, the CRI of ceramics with different Ce3+ concentrations varied from 63.5 to 76.1 and 60 to 67.7, respectively. Although CP05.04 had a high index, its color drift was severe and exceeded 10000 K. As a result, there is a significant imbalance in the ratio of yellow to blue light in the emitted light, resulting in a cold white light source. The CP05.04 sample is no longer suitable for lighting applications.
Fig. 9. The correlated CCT (a) and CRI (b) of the CP under different power density of laser irradiation.
As is widely known, phosphor materials may occur thermal quenching and reduce the luminous intensity during the progress of light-conversion [49,55,56]. Therefore, the surface temperature of the Al2O3/YAG:Ce CCP was recorded at an incident laser power density of 47.6 W/mm2, seen as Fig. 10. It could be observed that the operating temperature of the majority of the samples remained below 100 °C, indicating favorable heat dissipation performance due to the design of ceramics (Fig. 2) and stability of encapsulation (Fig. 6). This phenomenon could be elucidated by the following explanation: The final measured thermal conductivity of the Al2O3/YAG:Ce CCP with Ce3+ concentration of 0.10 at.% was 16.6 W m-1 K-1. The heat produced by the phosphor layer (YAG:Ce) was efficiently transferred to the adjacent Al2O3 layer due to their close proximity. The continuous-phase Al2O3 possessed a high thermal conductivity, enabling rapid transfer of the generated heat to the surrounding copper plate. These observations could also be attributed to the main reason for the absence of luminous saturation in the sample shown in Fig. 8. However, due to the significant temperature difference, the infrared imaging device was unable to capture it. In fact, the copper plate does have a certain temperature. At an incident laser power density of 47.6 W/mm2, it was evident that the temperature gradually increased with the thickness of the Al2O3/YAG:Ce CCP at the same concentration increased. On the one hand, the lower content of Ce3+ implied lower absorption, resulting in less heat generation. On the other hand, the increase in thickness expanded the range of blue light within the ceramics, leading to increased phosphor production. This, in turn, resulted in greater energy loss and subsequently higher heat generation. The above results showed that the Al2O3/YAG:Ce CCP had excellent thermal management performance and no thermal quenching occurred even at high power density.
Fig. 10. The temperature distributions at the laser spot for all samples under the power density of 47.6 W/mm2.
Figure 11(a) presents the luminous intensity of CP10.04 and 50 wt.% Al2O3-YAG:Ce CCP as a function of viewing angle to explore its practicality. CP10.04 and Al2O3-YAG:Ce CCP both exhibited similar Lambertian emission. Owing to the laminated design and waveguide structure of the CP10.04 sample, the beam underwent slight convergence, causing the majority of the light to be concentrated near 0 °, resulting in an enhanced central luminous intensity (59.17 cd > 45.71 cd) and a smaller beam angle (119.7 °<145.0 °). The above results confirmed that the laminated structural of the ceramics was advantageous for limiting the light path. From Fig. 11(b∼c), the forward light of CP10.04 produced a positive white light source compared to the Al2O3-YAG:Ce composite ceramic, with higher luminance, more uniform color and no yellow zone phenomenon [57]. The aforementioned findings indicate that ceramic luminous exhibiting a whiter and more uniform character would be better suited for scenarios such as laser flashlights and similar applications.
Fig. 11. (a) Luminous intensity as a function of the viewing angle for CP10.04 and 50 wt.% Al2O3-YAG:Ce CCP. The physical images of the space irradiation for (b) CP10.04 and (c) 50 wt.% Al2O3-YAG:Ce CCP, respectively.
4. Conclusion
In this study, a novel laminated structural Al2O3/YAG:Ce composite ceramic phosphor for high brightness laser lighting had been obtained using solid-phase sintering method. In comparison to conventional CCP, the front light emission efficiency of this laminated design was increased by 24.4%, which could be successfully used in transmissive package structure. Based on the optical and thermal performances, the CP10.04 (0.4 mm thickness, 0.10 at. % Ce3+ concentration) was the optimal ceramic, a high-performance front light source with a LF of 651 lm, LE of 144 lm/W, CCT of 6419 K and operating temperature as low as 84.9 °C was obtained, under the power density of 47.6 W/mm2. This study confirmed that through the alternate arrangement of Al2O3 and YAG:Ce, the propagation of blue laser light in the YAG:Ce material was effectively confined by TIR oscillations. Meanwhile, it was possible to change the phosphor emission angle, overcoming the limitations of TIR and enabling maximal emission of yellow phosphor from the ceramic surface, resulting in improved LE. Furthermore, the ceramics exhibited exceptional thermal performance attributed to the high thermal conductivity of the Al2O3 layer, facilitating rapid dissipation of heat. These results demonstrate that the promising potential of laminated structured Al2O3/YAG:Ce composite ceramic phosphor has the potential to be used in transmissive structures, such as automotive lighting and airport searchlights.
Funding
National Key Research and Development Program of China (2021YFB3501700); National Natural Science Foundation of China (52202135, 61975070, 52302141); Priority Academic Program Development of Jiangsu Higher Education Institutions (PAPD); Key Research and Development Project of Jiangsu Province (BE2023050; BE2021040); Natural Science Foundation of Jiangsu Province (BK20221226); International S&T Cooperation Program of Jiangsu Province (BZ2023007); Special Project for Technology Innovation of Xuzhou City (KC20201, KC20244, KC21379, KC22461); Open Project of State Key Laboratory of Crystal Materials (KF2205).
Disclosures
The authors declare no conflicts of interest.
Data availability
Data underlying the results presented in this paper may be obtained from the authors upon reasonable request.
Supplemental document
See Supplement 1 for supporting content.
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