Fabrication of red-emitting CaAlSiN3: Eu2+ through phosphor-in-glass approach for application in rear combination lamp
Graphical abstract
Introduction
In regards to the next generation lighting, white light-emitting diodes (LEDs) have attracted considerable interest due to remarkable characteristics with the advantages of high efficiency, long life, low power consumption, compact size and eco-friendly device for application in solid-state lighting such as automotive headlamps, display backlight and other lighting technologies [[1], [2], [3]]. Generally, white LEDs consists of phosphor as the color conversion materials with InGaN blue emitting chip, which is mixed with silicone to form a well-mixed phosphor composite for generation of white light. Despite this being the most common method for white light generation, there are numerous disadvantages such as thermal discoloration and poor reliability in long-term operation of silicon-phosphor mixture LEDs during operation of the high-power LED package [4,5]. Consequently, the increase of current leads to a decrease in LED efficiency, and there is an increasing need for high power LEDs in field of working light, traffic light and head lamp [6]. Based on the mentioned disadvantages, phosphor in glass (PiG) and ceramic phosphor plate (CPP), single crystal phosphor (SC) has a higher potential to solve the shortcomings of silicone-phosphor composite [[7], [8], [9], [10], [11], [12], [13], [14], [15]]. Both CPP and SC have garnered interests in regards to high power LED application due to high thermal quenching, mechanical and chemical characteristics. Although CPP and SC shows outstanding properties in high power LED, high power LED requires high sintering temperature of >1600 °C, high fabrication cost, and there is a limitation in terms of the type of phosphor materials used. As such, oxide phosphor such as Y3Al5O12: Ce3+ and Lu3Al5O12: Ce3+ are used to generate the white light. In conclusion, in the case of CPP and SC, it is realistically difficult to manufacture a light-emitting converter by mixing the different phosphor with nitride, sulphide, and oxynitride species for emission of a wide range of color.
The alternative is to use the PiG, which can be manufactured in relatively low-temperature processes to embody a variety of wide color range. The PiG consist of phosphor and glass materials with a low melting point. It is possible to fabricate PiG using CaAlSiN3: Eu2+, SrLiAl3N4: Eu2+ and β-SiAlON: Eu2+ phosphor [[16], [17], [18], [19]]. The PiGs can be sintered at relatively lower temperature <800 °C as compared to CPP and SC. For application in automotive lamp, particularly rear combination lamp (RCL), the PiG using CaAlSiN3: Eu2+ phosphor is applied on InGaN blue emitting chip. In this paper, PiG using CaAlSiN3: Eu2+ phosphor is abbreviated as RPIG. Until now, RCL with AlInGaP red emitting chip are not utilized for high-power LED application since it is used at relatively low temperatures. In addition, the luminous efficacy is dramatically decreased with an increasing in the junction temperature. The RPiG can be a good proposition for use in RCL application. Numerous researchers have studied the RPiG, however, there has been no reports associating the decrease of luminous efficacy in CaAlSiN3: Eu2+ phosphor to high temperature <550 °C [[20], [21], [22]].
This research presents an advanced research of the authors regarding RPiG using the glass frit which can be sintered at 380 °C, which optimized the contents of CaAlSiN3: Eu2+ phosphor based on the weight percent (wt%) of RPiG. The fabrication process and analysis regarding the luminous flux, conversion efficiency and color coordinates are performed and optimized. Finally, the possibility of LD application of RPiG is assessed.
Section snippets
Fabrication of RPiG
The RPiG as a function of CaAlSiN3:Eu2+ contents are fabricated with glass frit. The CaAlSiN3:Eu2+ phosphor (Intermatix, RR6644) and glass frit are used to fabricate the RPiG. CaAlSiN3:Eu2+ phosphor and low-temperature glass frit (SnO–ZnO–Al2O3–P2O5) were ball-milled with ZrO2 balls for 48 h and oven dried at 80 °C. The dried composites are uniaxially compressed under 20 MPa for 3 min. The pressed samples are sintered at 380 °C for an hour using gas pressure sintering (GPS) furnace. The
Results
Fig. 1 (a) shows the actual image of RPiG made using the low temperature glass matrix, while the XRD pattern analysis results compared with phosphor is presented in Fig. 1 (b). Most of the main peaks of the crystal structure of CaAlSiN3: Eu2+ phosphor corresponded with the results of the fabricated RPiG, and the diffraction angles confirmed to appear at about 31° were markedly low due to the glass amorphous broad diffraction spectrum at about 15–35°. The point EDS and mapping analysis of the
Conclusion
In summary, RPiG was successfully fabricated using the nitride phosphor CaAlSiN3: Eu2+ using red luminescence in combination with low temperature glass frit. Most high-efficiency red phosphors are nitrides, which are difficult to be applied in combination with glass materials. Our researchers solved this problem by utilizing low temperature glass frit and GPS atmosphere. The prepared RPiG has a FWHM of about 75 nm with the center wavelength of 645 nm and showed a PLQY of 92.8% when the phosphor
Declaration of competing interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgements
This work was supported by the Technology development Program (S2837664) funded by the Ministry of SMEs and Startups(MSS, Korea), and This research was supported by a grant (19CTAP-C152269-01) from Technology Advancement Research Program (TARP) funded by Ministry of Land, Infrastructure and Transport of Korean government.
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These authors contributed equally to the work.