Yiming Liu

The study of luminescence properties on Ce:YAG phosphor in glass co-sintered at different temperatures

Ce:YAG phosphor in glass was prepared by co-sintering bismuthate glass frits and Ce:YAG phosphors at different temperatures in the 550–800xa0°C range. In this work, the effect of co-sintering temperature on the photoluminescence and chromaticity coordinates (CIE) of phosphor in glass was investigated. The results show that the CIE coordinates is tunable with the increase of co-sintering temperature. As temperature increased from 550 to 700xa0°C, the intensity of emission and excited peak increases until a maximum is reached, after which it rapidly drops off. The degradation of luminescence properties with the higher co-sintering temperature is due to the broken lattice surrounding the Ce3+ and oxidation of the Ce3+ caused by the reactions between the bismuthate glass and Ce:YAG phosphors.

Effect of phosphor composition and packaging structure of flexible phosphor films on performance of white LEDs

YAG:Ce3+ phosphor and CASN:Eu2+ phosphor were synthesized by conventional solid-state reaction, and the phosphor films were prepared from the synthesized YAG:Ce3+ phosphor and CASN:Eu2+ phosphor by a simple spin coating method. The influence on the concentration of the red phosphor and the different packaging structure of the phosphor films on the optical and electrical properties of white LEDs were investigated. The red and green phosphor were coated layer by layer to investigate the spectral absorption effect of phosphors in the films. The phosphor film placing green phosphor adjacent to the chips is named as G–R structure, likewise, the red phosphor close to the chips is labeled as R–G structure. The results show that the emission spectra of the phosphor films with G–R structure exhibit obvious red shift with the increase of the proportions of red phosphor due to the red phosphor have a reabsorption effect on the green light. Then, the phosphor films with G–R and R–G structures were packaged on the LED respectively, and the light efficiency and the correlated color temperature (CCT) of the LEDs gradually decrease with the increase of the proportions of red phosphor. The luminous efficacy of LEDs packaged by G–R structured phosphor film is higher than that of LEDs packaged by R–G structured phosphor film. The luminous efficiency of LEDs packaged by G–R structured phosphor film can reach 128.95xa0lm/W, the CCT is 4458xa0K, and the CRI is 65.1. Moreover, the CCT uniformity of LEDs packaged by G–R structured phosphor film is superior to that of LEDs packaged by R–G structured phosphor film. Therefore, the G–R structured phosphor film has potential application values for improving the luminous efficiency and light uniformity of the device.

High color rendering index of warm WLED based on LuAG: Ce 3+ PiG coated CaAlSiN 3 : Eu 2+ phosphor film for residential lighting applications

The high color rendering index of warm white light-emitting diode (WLED) was fabricated using LuAG: Ce3+ PiG coated CaAlSiN3: Eu2+ phosphor film as converted materials. The LuAG: Ce3+ PiG and CaAlSiN3: Eu2+ phosphor film was prepared by low-temperature co-sintering and spin coating route, respectively. In this work, the thermal stability of LuAG: Ce3+ PiG through the thermal shock test was discussed. After that, the optical properties of Lu2.94−xYxAl5O12: 0.06Ce3+ (xu2009=u20090, 0.2, 0.4, 0.6, 0.8) PiG coated CaAlSiN3: Eu2+ phosphor film converted WLEDs were investigated. When x value is 0.4, it exhibits a color rendering index of 94, correlated color temperature of 3087xa0K and luminous efficiency of 62xa0lm/W under 20xa0mA current driving. The package method has excellent developing potential for residential lighting applications.

Analysis of high-temperature aging and microstructure of FC LED solder joints of a silver conductive layer bonded using SAC solder

Flip-chip (FC) light-emitting diode (LED) filaments with a silver conductive layer are impeded by heat dissipation, with the flip-chip junction temperature of reaching up to 423.15 K. To overcome this problem, we simulated aging of SAC305 solder joints at a high temperature of 433.15 K. Scanning electron microscopy was performed to analyze the changes in the microstructure of the solder joints with aging time. Moreover, energy-dispersive X-ray spectroscopy was performed to analyze changes in the element content of the solder joints with aging time. The shear force of solder joints was measured using a strength tester. Results revealed that the Ag/Au content of the solder joints increased under the high-temperature conditions, resulting in the formation of cracks and holes in the solder joints. Furthermore, the reliability of the FC LED filaments was affected by the maximum shear stress that can be tolerated by the solder joints.

Optical and thermal properties of flip-chip LED bulbs using chip-scale package

A kind of LED bulb which is made by the school and enterprise is introduced in this paper. Fluorescent film is used for chip-scale packaging on flip-chip LED. The film is made by spin coating method, bonded to the surface of the chip and cut off by laser and then finished by a simple process. The optical properties and thermal properties of the LED bulbs were measured by various methods. The experimental results showed that with the increasing of the voltage, color temperature and the color rendering index changing 0.522% and 0.200% respectively which can be seen as a relatively stable data. The highest surface temperature of the flip-chip LEDs using chip-scale package we estimated which can be kept between 133.8°C and 135 °C can also be accepted. These results have a certain guiding significance for the industrialization of the LED bulbs.

Reliability of fluoride phosphor K2XF6:Mn4+ (K2SiF6:Mn4+, K2(Si,Ge)F6:Mn4+, K2TiF6:Mn4+) for LED application

The red fluoride phosphor K2XF6:Mn4+ was prepared by co-precipitation with partial HF in placed with glacial acetic acid. The phase structures and photoluminescence (PL) properties of the red fluoride phosphor K2XF6:Mn4+ phosphor have been investigated in detail. Reliability test show that the relative PL intensity of KSFM, K(S,G)FM and KTFM decreased by 14.95%, 18.22% and 67.21% after the ambient condition of high temperature and high humidity (85xa0°C/RH 85%) for the exposure time of 168xa0h. The thermal cycling testing results show that the relative PL intensity of KSFM, K(S,G)FM and KTFM decreased by 0.41%, 5.55% and 1.14% after storing the phosphors into an ambient condition of 120xa0°C for 1xa0h and −u200940xa0°C for 1xa0h by turns for five times. The relative PL intensity of KSFM, K(S,G)FM and KTFM decreased by 89.09%, 91.93% and 99.94% after soaking into boiled water for 3xa0h. It can be summarized that KSFM has the best reliability and KTFM has the worst reliability. Then by mixing the YAG:Ce3+ and KXFM phosphor and commercial green phosphor with appropriate proportion of the components, it can be found that the luminous efficacy of K2XF6:Mn4+ (KSFM, K(S,G)FM, KTFM) after 85°C/RH 85% decreased by 0.14%, 0.54% and 1.06%, after thermal cycling decreased by 2.60%, 1.53% and 3.17% and after hydrolysis decreased by 14.49%, 9.65% and 47.66%. The KTFM after hydrolysis and YAG:Ce3+ encapsulated WLEDs have the most reduced luminous efficacy. Moreover, the luminous efficacy of K(S,G)FM after hydrolysis and YAG:Ce3+ encapsulated WLEDs is better than KSFM after hydrolysis and YAG:Ce3+ encapsulated WLEDs.