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Abstract
High-power, high-brightness laser lighting promotes new requirements for light-conversion materials, such as high thermal conductivity, high saturation threshold and compact encapsulation. In this paper, we designed and fabricated a novel composite structure ceramic including a 1.0 × 1.0 mm2 Al2O3-YAG:Ce ceramic and a φ=16.0 mm transparent YAG ceramic for the transmissive configuration in laser lighting. When pumped by blue laser from 0∼60 W mm2, all the samples exhibited no luminous saturation phenomenon, and the 10.0 wt.%Al2O3-YAG:Ce/YAG composite ceramic with the thickness of 0.3 mm maintained white light with a luminous efficacy over 200 lm/W. Moreover, a maximal luminous flux over 1000 lm, a correlated color temperature (CCT) of 5471 K, and an operating temperature as low as 92.3 °C were obtained under the excitation power density as high as 60 W/mm2. The configuration that Al2O3-YAG:Ce encapsulated by YAG reflects an excellent optical and thermal properties by using transparent and highly thermally conductive YAG materials. These results indicate that Al2O3-YAG:Ce/ YAG composite ceramic phosphor is a promising candidate in transmissive configuration for automotive lighting and laser searchlight.
© 2022 Optica Publishing Group under the terms of the Optica Open Access Publishing Agreement
1. Introduction
Laser-driven lighting possesses superior properties including high power, high brightness, high collimation [1,2], and then has great advantages in new technologies, such as automotive headlamps, airport lighting, searchlight, and projection [3,4]. In the reflective configuration model, the highest luminance could be often generated through the collimated blue laser diodes (LD) remotely activating yellow luminescent materials, which are encapsulated on a copper substrate by solder [5–7]. Generally, the luminescent materials are required to be nontransparent and highly reflective to improve the light extraction efficiency [8]. The most typical application of this configuration is laser projector [7]. However, because of inconsistent path between the blue laser and the yellow fluorescence, the reflective configuration exposes some shortcomings, including complex beam shaping, poor lighting uniformity and large volume.
The transmissive configuration controls the transmission direction of the blue laser to coincide with the fluorescence, and it becomes the desirable model for compact laser lighting. In addition, as the core part of LD lighting device, the luminescent materials exists various encapsulation forms, including the phosphor-in-silicone (PIS) [9], phosphor-in-glass (PiG) [10–12], ceramic phosphor (CP) [13–16], etc. As known, PIS has the lowest thermal conductivity (0.1∼0.4 W·m-1·K-1), causing thermal focusing and high temperature of itself on the laser spot. Besides, the carbonization of silicone is easy to occur (exceeding 150°C) under the high power-density laser excitation [17,18]. However, the carbonization phenomenon would never be observed in the inorganic materials. PiG is made by transparent glass and phosphor. Its preparation process is very simple, and the chromaticity parameters including CCT and CRI are also very convenient to regulate just by choosing different phosphors [19]. However, its thermal conductivity is also not very high (1.0∼3.0 W·m−1·K−1) [20], which can not suffer the high power (≥5.0 W) and high density (≥10W/mm2) excitation. CP has the relatively high thermal stability and thermal conductivity (9.0∼14.0 W·m−1·K−1), and it becomes good candidate for high power LD lighting.
In addition to the key requirement of high thermal conductivity for the luminescent materials, an outstanding optical system and an excellent heat-dissipation system are essential in the transmissive configuration. Firstly, because of the highly collimated laser beam, CP is usually made to be translucent for light scattering [21,22]. That´s means the secondary phase acts a scattering center which reduce the transmittance of CP to change the propagation direction of blue laser for achieving a more efficient and more uniform white light. Besides, the secondary phase has an great influence on the improvement of thermal stability, such as Al2O3 (32∼35 W m-1 K-1) [23–26], MgO (47.2∼53.5 W m-1 K-1) [27], AlN (320 W m−1K−1) [28–31], which is beneficial for composite ceramics to heat dissipation. Secondly, the size of CP is generally in the millimeter level to control the spot diameter of white light source, which is the main reason why we pursue higher power density of CP in laser lighting system, such as automotive lighting [4]. In our previous reports, chip-level Ce:GdYAG CP (2.5 × 2.5 mm) based white LED devices with high brightness were assembled for automotive and high-speed rail lighting applications [32]. A luminous flux of 2000 lm, a correlated color temperature (CCT) of 6266 K were obtained. However, its highest power density was only 1.76 W/mm2 and the size of ceramics should be smaller for the applications of laser lighting. Finally, the encapsulation material should have the proprieties of high transparency and high thermal conductivity, and show no affection of the absorption and emission for the luminescent material [33].
Unfortunately, the solder and other connecting materials for encapsulation of luminescent materials for reflective configuration are mostly opaque [7,34], which could not be used in transmissive configuration. Recently, to solve this problem, Lenef’s group designed the Al2O3-YAG:Ce/Al2O3 structure for laser lighting [35]. By confining a low-scattering CP conversion region within a high-scattering Al2O3 substrate (opaque materials), the co-sintered ceramic can operate stably under the excitation of 4.3 W laser. The highest luminous illumination value of 600 lm and the corresponding peak luminance of 500 cd/mm2 was observed. This packaging method is an effective way for chip-level ceramics (φ= 0.5 mm). However, the opaque and porous material reduces the luminous efficiency (only 150 lm/W) of the ceramic. Meanwhile, the bottom of the luminescent material cannot be encapsulated with Al2O3 porous material to really ensure the absorption of blue laser, and only the surrounding boundary was bonded, which seriously limited the effective area for heat dissipation. In addition, the sapphire is discovered as the optimized substrate for luminescent material due to its high thermal conductivity (∼30 W m−1 K−1) and high in-line transmittance (∼86%) [36,37]. Xie, et.al. developed an architecture that a PiG film was directly sintered on a high thermally conductive sapphire substrate [33]. This PiG film can even be survived under the 11.2 W mm−2 blue laser excitation and have a high luminous efficiency of 210 lm/W. However, due to the difficulty of thermal bonding and the difference of sintering conditions between the CP and sapphire, it is difficult for ceramics to be sintered on sapphire, which has also not been reported so far. Therefore, it is essential to find a transparent material who has high thermal conductivity to encapsulate the luminescent ceramic, and offsets the defects of optical system and thermal system for laser lighting.
In this paper, the CP with a novel Al2O3-YAG:Ce/YAG composite structure were designed and fabricated using the two-steps sintering. Owing to the effectively connecting with the periphery and the bottom of Al2O3-YAG:Ce composite ceramic by transparent YAG ceramic, the CP exhibited good optical and thermal properties. Besides, the transparent YAG substrate could not affect the incidence of the laser and the output of fluorescence, respectively. The luminous flux, luminous efficiency, and correlated color temperature (CCT) were also studied in detail by combining the CP and a high-power blue LD. The samples exhibited no luminous saturation when the pumped power density even reached 60 W mm2. Additionally, by adjusting the thickness of ceramics and the content of Al2O3 in Al2O3-YAG:Ce luminescent ceramics, a high brightness light source with the luminous flux over 1000 lm, luminous efficiency of 210 lm/W, CCT of 5471 K, and the operating temperature as low as 92.3 °C was obtained. These results confirm that the Al2O3-YAG:Ce/ YAG composite CP is a promising candidate for laser lighting.
2. Experimental method
The 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%) were used as the raw materials. Firstly, the designed Al2O3-YAG:Ce composite CP with the different contents of Al2O3 in the range of 5.0–30 wt. % (Al2O3/ Al2O3- YAG:Ce) was prepared by the vacuum solid-state sintering method, and the concentration of Ce3+ in YAG:Ce was set to be 0.2 at. %. The raw materials (Al2O3- YAG:Ce) were mixed for 12 h with a rotation speed of 180 rpm by using alcohol as a dispersant and Al2O3 balls as the grinding media, respectively. After drying at 55°C for 12 h, the mixture was dry pressing at 20 MPa in a die with a diameter of 20 mm, and then cold isostatically pressed under 200 MPa for 10 min. At last, the green bodies were sintered at 1770°C for 8 h in the vacuum (<10−4 Pa). The annealing was conducted at 1350°C for 10 h to remove the internal stress and eliminate oxygen vacancies. Here, the diameter of Al2O3- YAG:Ce composite CP was 16.0 mm. Secondly, the composite CP were mirror polished and cut to 1.0 × 1.0 × 1.0 mm for further sintering. Thirdly, the raw materials (YAG) were weighed precisely in accordance to the Y3Al5O12 formula, and then ball milling for 12 h with a rotation speed of 180 rpm by using alcohol as a dispersant and Al2O3 balls as the grinding media, respectively. After drying at 55°C for 12 h, the mixture was dry pressing together with Al2O3-YAG:Ce composite CP at 20 MPa in a die with a diameter of 20 mm. Finally, both sides of the ceramic plate were carefully machined and polished. The thicknesses of Al2O3-YAG:Ce/ YAG composite CP were 1.1 mm while Al2O3-YAG:Ce were processed to 0.15 mm, 0.2 mm, 0.3 mm. The detailed fabrication processes of CP is described in Fig. 1. The nomenclature of samples with different ratios of Al2O3 content is listed in Table 1.
Table 1. Nomenclature of samples with different ratios of Al2O3 content
The morphologies of samples were characterized by a scanning electron microscopy (SEM, JSM-6510, JEOL, Tokyo, Japan) and a light microscope (FXD-30 MW, Shandong, China), respectively. The in-line transmission spectra of the polished CP were characterized by an UV-Vis-NIR spectrophotometer (Lambda 950, Perkin Elmer, USA). A fiber coupled blue LD with maximum output power of 4.68 W (4 A) and the NA = 0.22 was used. The core diameter was 200 microns. The angle of divergence of the laser could be calculated according to the formula as follows: NA = n·sina, where NA was numerical aperture, n was refractivity of core diameter, a was angle of divergence. Therefore, the laser-irradiated spot was approximately circular with diameter of 0.314 mm at a distance 1.1 mm. The input power density of LD was calculated by dividing the input power of LD by the area of laser-irradiated spot. The luminous flux, CCT and CRI values under different power densities were tested using an integrating sphere (HASS-2000, Hangzhou, China). The luminous intensity was characterized by space spectroradiometer (GO-SPEX500, Hangzhou, China). The fluorescence decay was characterized by a fluorescence spectrometer (OmniFluo 900, Beijing, China) The surface temperature distributions of the CP were measured by an infrared camera (Fotric 225s, Fotric, America).
3. Results and discussion
Figure 2(a) depicts the photographs of all fabricated Al2O3-YAG:Ce/ YAG CP. The words “YAG/Al2O3-YAG:Ce” on the paper could be clearly seen by naked eyes, indicating the excellent transparency of YAG part. Under 450 nm blue light, the emitting area and non-emission region could be clearly identified in Fig. 2(b). The optical transmission micrograph in Fig. 2(c) shows the clear boundary between YAG part (right) and Al2O3-YAG:Ce ceramic part (left), and the SEM image of the interface in Fig. 2(d) shows a closely and strongly bonded interface. The above results mean that the non-luminescent and transparent YAG part as the substrate material could encapsulate the Al2O3-YAG:Ce ceramic perfectly without affecting the fluorescence emission behavior.
Fig. 2. Images of the Al2O3-YAG:Ce/ YAG ceramics under (a) daylight and (b) 450 nm blue light (using a blue light filter for camera); (c) Optical transmission micrograph and (d) SEM image at the boundary between Al2O3-YAG:Ce part and YAG part of CP05.15 sample
For detailed analysis of photoluminescence properties, Fig. 3(a), (b) displays the optical configuration in our experimental mainly included a fiber coupled blue LD, substrates and Al2O3-YAG:Ce/ YAG ceramics. The CP were placed directly above the terminal of optical fiber, showing a transmissive configuration, to obtain a high-brightness light source. The incident power density of CP was as high as 60W/mm2. Figure 3(c) shows the photograph of the samples under blue-laser excitation. There was no residual laser beam in the mixed white light, which proved that the radius of the laser spot (φ= 0.314 mm) was smaller than the size of the luminescent ceramic part (1.0 × 1.0 mm).
Figure 4 shows the electroluminescence (EL) spectra of Al2O3-YAG:Ce/YAG composite CP under laser excitation of 1.0 W (13 W/mm2). A narrow emission band ranging from 450 to 455 nm and a broad emission band from 500 to 750 nm were observed, which attributed to the stimulated radiation of LD and the 5d-4f transitions of Ce3+ ion, respectively [9,38]. It is also noticed that the content of Al2O3 exerts a significant influence on the spectra characteristics. For the Al2O3-YAG:Ce/YAG CP with the thickness of 0.15 mm (CP05.15- CP30.15), the residual blue light increased gradually with the increasing content of Al2O3 from 5.0 to 30.0 wt.%, and it caused the lighting color changing from warm white to cold white, as shown in the inset of Fig. 4. The trend remained unchanged at the thickness of 0.20 mm and 0.30 mm. Fig. S1 (in Supplement 1) shows that the in-line transmittance of the CP (0.30 mm, 5.0 ∼30 wt.% Al2O3). As increasing the Al2O3 content, the in-line transmittance in the visible wavelength range was increased, while the absorption at blue region was declined. Higher in-line transmittance and lower absorption of CP would cause more residual blue light in LD light source, and this was in accordance with the EL spectra. These phenomena can be explained that with the increase of alumina content, there exists a decrease of the absolute value for Ce3+ ion within the same volume and it reduces the absorptivity and the corresponding light-conversion efficiency of the materials. The scattering centers in ceramics, especially Al2O3, are beneficial to scatter the blue laser and improve the light-conversion efficiency [39,40]. However, when the thickness of ceramic was thinner, the content of Ce3+ played a dominant effect for light-conversion efficiency compared with the scattering enhancement effect of Al2O3. Interestingly, the sample of CP10.30 (Al2O3= 10 wt.%, d = 0.30 mm) had higher fluorescence intensity than that of CP05.30 (Al2O3= 5.0 wt.%, d = 0.30 mm), and this might be own to an increasing scattering effect by secondary phase after the thickness increased.
Fig. 4. Electroluminescence spectra of Al2O3-YAG:Ce/ YAG composite CP under laser excitation of 13.0 W/mm2 (laser power of 1.0 W). The inset was the enlarged view of fluorescent area and the corresponding lighting images
The luminous flux of the samples dependent on different laser power densities are depicted in Fig. 5(a). The highest luminous flux over 1000 lm was obtained for the CP05.30 (Al2O3= 5.0 wt.%, d = 0.30 mm), CP10.30 (Al2O3= 10.0 wt.%, d = 0.30 mm) and CP15.30 (Al2O3= 15.0 wt.%, d = 0.30 mm) by a 4.68 W blue laser in this transmissive configuration. Compared with other ceramics (d = 0.15 and 0.20 mm), the thicker ceramics (d = 0.30 mm) had the higher luminous flux due to higher absorption of blue-light area. Besides, the luminous flux linearly increased with the increase in power density (0∼60 W/mm2) and the luminous saturation threshold was never observed in the Al2O3-YAG:Ce/YAG composite CP. It is the well-known that luminous saturation is a common phenomenon in laser lighting, and the saturation power density of Al2O3-YAG:Ce composite ceramics can reach 50 W/mm2 [39,41]. In our paper, the concentrations of Ce3+ in all samples were 0.2 at.%. The low Ce content has positive implications for both intensity quenching and thermal quenching [42,43]. We also carried out the relevant research work and found that: when the Ce content ≥0.2 at.%, the behavior of luminous decline starts to appear [15]. Much higher Ce has an advantage to adjust for color points (for higher CRI), but with the consequential impact of worse thermal and intensity quenching. For the applications of high CIR, adopting moderate Ce content and introducing ions (e.g., Mn2+) for red emission may be the better solution [44,45]. Besides, Xu et.al. found that the luminous saturation threshold had a relationship between the intensity of incident power and power density [46]. The luminous saturation threshold of luminescent materials would not appear until the power density increased to 300 W·mm2 at low incident power (∼3.0 W). However, a sudden decrease of luminous flux for the luminescent materials was observed in a new irradiation environment with a laser when the total power was 10.0 W and the power density was 4.0 W/mm2 [46]. In this paper, the enhancement of luminous flux was continuously discovered in the CP as the incident blue power increased from 0 to 4.6 W (0∼60 W/mm2 for power density), indicating that no luminous saturation appeared. This result greatly meets a technical requirement for automobile and flashlight lighting.
Fig. 5. (a) Luminous flux and (b) luminous efficacy for the CP encapsulated devices as a function of the incident laser power density
As can be seen from Fig. 5(b), all the samples have high luminous efficiency (150∼210 lm/W), which was almost the highest value in the transmissive configuration model. Thanks to the small size (1.0 × 1.0 mm) of Al2O3/YAG:Ce, the self-emitted fluorescence could be escaped from the transparent YAG ceramics. Besides, the fluorescence lifetime τ of the samples were around 59.8 ns, which is near to the Al2O3-YAG:Ce composite ceramics (64.7 ns, seen as Supplement 1, Fig. S2) with same size, so the non-luminescent YAG materials could encapsulate the Al2O3-YAG:Ce ceramic perfectly without affecting the fluorescence emission. On the contrary, in the previous reports, the excitation area of Al2O3/YAG:Ce composite CP with large-scale (φ∼16 mm) was generally much less than 1.0 mm2 [47], and this meant that the CP could be understood as a small luminous point (1.0 mm2) and encapsulated with a large opaque material (φ∼16 mm). More fluorescence was trapped inside the ceramics, which resulted in a decline of luminous efficiency. Moreover, the backward direct emission is somehow redirected in the forward direction due to the total internal reflection of transparent YAG ceramics. Therefore, a high brightness light source with the luminous flux over 1000 lm, luminous efficiency of 210 lm/W was obtained here in the transmissive configuration by encapsulating with CP05.30, CP10.30 and CP15.30.
Figure 6 shows the CCT and the corresponding color coordinates on the CIE-1931 chromaticity diagram of the CP under laser irradiation, respectively. As the increase of thickness from 0.15 to 0.3 mm, the CCT of CP with different Al2O3 contents were changed in the ranges of 6070∼5130 K, 6422∼5124 K and 20000∼7433 K, respectively (under 5.0 W/mm2). It convinced that 0.3 mm was the optimal thickness for achieving appropriate CCT of warm-white light and highest luminous flux. This could also be seen from the luminous flux data (∼1000 lm) in Fig. 5(a). Innovatively, nearly all CCT data was stable with the change of power density, indicating the stable emission color when the power density increased to 60 W/mm2. However, the samples with 30% of Al2O3 had an obvious color shift from 12964 K to 20000 K for CP30.20, and from 7433 K to 9461 K for CP30.30, respectively, and the cool-white light sources could be obtained due to the low content of Ce3+. It is well known that the influence of residue blue light on color coordinates is more obvious in cool-white lighting source compared to that of warm-white light source [48]. Although the amplitude of chromaticity shift for the samples with a thickness of 0.3 mm was almost consistent with other samples of 0.15 mm or 0.2 mm, their deviation values for CCT were greater. It can be clear seen by the color coordinate diagram in Fig. 6. Fortunately, the color coordinates of all the samples were distributed around the Planckian curve and gradually moved to the yellow region with the increase in thickness.
Fig. 6. CCT and the corresponding color coordinates of CP encapsulated LD in Fig. 3(a) under laser irradiation. Table S1 gives the specific values of color coordinates
In fact, the thermal quenching effect of luminescent material is an adverse factor in laser lighting and it can greatly deteriorate the luminous intensity [43,49,50]. Figure 7 presents the surface temperature at the laser spot for the samples as the incident laser power density is 60 W/mm2. All luminescent materials (Al2O3/YAG:Ce) operated well below 100 °C, indicating the good heat dissipation performance. The inset of Fig. 7 shows the temperature distribution of the whole ceramic. The high temperature distribution area in the center of ceramic was similar to the size of laser spot (φ= 0.314 mm) and it diffused to the edge in a circle. Above results indicated that the CP had good thermal management performance and the heat induced luminescence quenching would not occur even under the power density of 60 W/mm2. This may be explained as follows: because the Al2O3/YAG:Ce composite ceramics have high thermal conductivity (≥9.0 W·m-1K-1) [22], and the heat produced by themselves can quickly transfer to the surrounding encapsulation materials. In addition, the transparent encapsulation materials (YAG) also had a high thermal conductivity (∼14.0 W·m-1K-1) and showed a whole combination with luminescent material part (Al2O3/YAG:Ce) by sintering, and this is very beneficial for heat conduction. This was actually our original design idea for the high-brightness LD lighting in the transmissive configuration model, and it was successfully realized through the mentioned composite structure. In fact, the excellent property of heat dissipation was the main reason why the samples appeared no luminescence saturation in Fig. 5(a). Besides, the surface temperatures of the CP with increasing the content of Al2O3 were declined from 91.8 °C to 77.4 °C for the thickness of 0.15 mm, from 99.6 °C to 88.2 °C for 0.20 mm, from 99.0 °C to 87.9 °C for 0.30 mm, respectively. On the one hand, the lower content of Ce3+ means the lower absorption [38], and this suggests the less heat is generated. On the other hand, the increase of Al2O3 content in Al2O3/YAG:Ce ceramics would improve the thermal conductivity, and it is also beneficial for heat dissipation [23,40]. Meanwhile, as the increasing of the thickness from 0.15 mm to 0.30 mm, the surface temperatures of the CP were increased. Because of the stronger capacity of absorption for blue laser, the thicker samples produced more fluorescence and the corresponding energy loss, which accompanied with more heat. The temperatures at the laser spot of CP05.30, CP10.30 and CP15.30 were 99.0 °C, 92.4 °C and 92.3 °C when the power density reached 60 W/mm2, respectively. The temperature variation for the samples under the power density of 0∼60 W/mm2 are shown in Fig. S3 (Supplement 1). Combined the CP15.30 with a 4.68 W blue laser, a high brightness light source with the luminous flux over 1000 lm, the luminous efficiency of 210 lm/W, the CCT of 5471 K, and the operating temperature of 92.3 °C was obtained.
Fig. 7. The temperature variation at the laser spot for the samples under the power density of 60 W/mm2. The inset was the heat distribution of the whole ceramic
Figure 8(a) shows the luminous intensity as a function of the viewing angles for CP10.30 and 10 wt.% Al2O3-YAG:Ce composite ceramic (φ=16 mm, before cutting into 1.0 × 1.0 mm). Without a secondary optic system, the CP10.30 showed no Lambert emission like Al2O3-YAG:Ce composite ceramic. As mentioned above, the fluorescence of luminous area can escape from transparent YAG to result in a higher luminous flux. Most of light were sit at 270 °∼315 ° and 45 °∼90 °, and this causing the peripheral intensity higher than that of Al2O3-YAG:Ce. However, the above results are not favorable for light spot limitation. As can be seen in Fig. 8(b), (c), compared with the Al2O3-YAG:Ce composite ceramics, the scattering in the CP10.30 is more serious (φ=16.0 mm>12.0 mm) and this lead to a lower luminous intensity (92.73 cd<143.5 cd) and larger beam angle (169.9 °>116.3 °). Besides, as described in transparent ceramics for laser illumination reported [51], the samples have a yellow area on the side, in Fig. 8(b). Fortunately, the forward light of CP10.30 forms a positive white source instead of yellow source. Through the reasonable optical design, a white light source with good beam quality can be obtained.
Fig. 8. (a) Luminous intensity as a function of the viewing angle for CP10.30 and 10 wt.% Al2O3-YAG:Ce. (b∼c) The diagrams of the space irradiation of CP10.30 and 10 wt.% Al2O3-YAG:Ce, respectively. The inserted table was the relevant luminous parameters
The prototype device of modular LD is shown in Fig. 9. It was a simple combination of CP15.30 and blue LD, and it illuminated a construction site. To enhance the irradiation distance and the irradiation area, a collimator lens (glass, η≈90%, φ=59.0 mm, f = 60.0 mm, in Fig. 9(a)) and a parabolic reflector (aluminum, η≈95%, the height of 40.0 mm, bottom opening diameter of 9.0 mm, top opening diameter of 55.0 mm, in Fig. 9(b)) were adopted, respectively [52,53]. A small spot-light source and a large spot-light source were obtained by using a collimating lens and a parabolic reflector, respectively, and it showed great potential for laser flashlight, headlight, outdoor searching and rescue, and so on. Subsequently, we will carry out the reflective configuration in Supplement 1, Fig. S4 and explore its luminous proprieties. All results above validate the suitability of Al2O3-YAG:Ce/YAG composite CP as a smart structure for high-brightness laser-driven lighting.
Fig. 9. Demonstration images of illuminating a construction site by (a) narrow beam and (b) broad beam from the LD lighting device fabricated with CP
4. Conclusion
In summary, a novel Al2O3-YAG:Ce/YAG composite ceramic phosphor with extremely high lumen density for high-brightness laser lighting was obtained using two-step vacuum solid-state sintering method. The investigations showed that the CP exhibited no luminous saturation even under the laser power density of 60 W/mm2. Moreover, the high luminous efficiency of 210 lm/W was obtained in the transmissive configuration due to the transparent encapsulation material of YAG. More importantly, owing to the effectively bonding with the periphery and the bottom of the Al2O3-YAG:Ce composite ceramic by transparent YAG, the CP assembled devices exhibited the excellent thermal performance. The surface temperature of the samples at the laser spot was just 99.8 °C under the high power density of 60 W/mm2. By adjusting the thickness of luminescent ceramics and the content of Al2O3 in Al2O3-YAG:Ce luminescent ceramics, a high brightness light source with the luminous flux over 1000 lm, luminous efficiency of 210 lm/W, CCT of 5471 K, and the operating temperature of 92.3 °C was obtained. These results indicate that Al2O3-YAG:Ce/ YAG composite ceramic phosphor is a promising candidate in transmissive configuration for automotive lighting and laser searchlight.
Funding
Key Technologies Research and Development Program (2021YFB3501700); National Natural Science Foundation of China (51902143, 52202135, 61971207, 61975070); Priority Academic Program Development of Jiangsu Higher Education Institutions; Jiangsu Provincial Key Research and Development Program (BE2019033, BE2021040); Natural Science Foundation of Jiangsu Province (BK20191467, BK20221226); Graduate Research and Innovation Projects of Jiangsu Province (KYCX22_2845); International Science and Technology Cooperation Program of Jiangsu Province (BZ2019063, BZ2020030, BZ2020045); Natural Science Research of Jiangsu Higher Education Institutions of China (19KJB430018, 20KJA430003); Xuzhou Science and Technology Program (KC19250, KC20201, KC20244, KC21379); State Key Laboratory of Advanced Materials and Electronic Components, Guangdong Fenghua Advanced Technology Holding (FHR-JS-202011017).
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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