Effect of different bending shapes on thermal properties of flexible light-emitting diode filament

Heat dissipation is an important part of light-emitting diode(LED)filament research and has aroused constant concern.In this paper,we studied the thermal performance of flexible LED filament by numerical simulation and through experiment.The heat dissipation characteristics of spring-like structure flexible LED filament were computed by finite volume method,and it was found that the chip junction temperature was closely related to the pitch and the bending radius.The effect of inclination angle of lighting LED filament was discussed because it is relevant to the spring-like structure flexible LED filament in geometry.The results demonstrated that the temperature of the filament increases as the inclination angle improves.

Development of optical-thermal coupled model for phosphor-converted LEDs

In this review, first, we discussed the effect of phosphor features on optical properties by the software simulation in detail. A combination of these parameters: phosphor material, phosphor particle size and particle distribution, phosphor layer concentration, phosphor layer thickness, geometry, and location of the phosphor layer, will result in the final optical performance of the phosphor layer. Secondly, we introduced how to improve light extraction efficiency with various proposed methods. Thirdly, we summarized the thermal models to predict the phosphor temperature and the junction temperature. To stabilize the optical performance of phosphor-converted light emitting diodes (PC-LEDs), much effort has been made to reduce the junction temperature of the LED chips. The phosphor temperature, a critical reliability concern for PC-LEDs, should be attracted academic interest. Finally, we summed up optical-thermal coupled model for phosphors and summarized future optical- thermal issues exploring the light quality for LEDs. We foresee that optical-thermal coupled model for PC-LEDs should be paid more attention in the future.

Optical and scintillation properties of Bi_4Si_3O_(12):RE(RE=Eu^(3+), Sm^(3+),Ho^(3+), Tb^(3+))single crystals

Bi_4 Si_3 O_(12):RE(BSO:RE, RE = Eu^(3+), Sm^(3+), Ho^(3+), Tb^(3+)) crystals were grown by the modified vertical Bridgeman method, and doping effects on scintillation properties were investigated. Under γ-ray irradiation, the light yield of BSO doped with small doses of Eu^(3+) increases slightly, and the energy resolution improves significantly compared to pure BSO, therefore the ability of distinguishing between particles will be improved for BSO crystals with a small amount of Eu^(3+) dopant. The results show that a small amount of Eu^(3+) doping can sensitize the Bi^(3+) ions. The sensitization effect enables the reduction of intrinsic defects, and thus improves the scintillation properties. However, the relative light yield of BSO:Tb(1.0 mol%) crystal is 4.3%, which is smaller than 5.0% of pure BSO. The improved light yield and energy resolution in the BSO:Eu and BSO:Sm crystals are considered an impressive achievement in the optimization of this scintillator which is already suitable for applications such as dual-readout calorimeters and homogeneous hadron calorimeters.

Effect of reduction co-sintering on the photoluminescence properties of phosphor in glass in boro-bismuthate glass

Phosphor in glass（PiG） employing Ce:Y3Al5O12（YAG）-doped boro-bismuthate glass via low-temperature cosintering technology was successfully prepared, using Bi2O3-B2O3-ZnO glass as the base material. The photoluminescence（PL） of PiG co-sintered at times ranging from 20 min to 60 min at 700°C was investigated.As a result, the relative PL intensity of PiG under a reducing atmosphere of CO showed significant enhancement of about 7–14 times that under air atmosphere sintering for 20–50 min. The PL intensity decreased gradually with the co-sintering time, which may be due to the corrosion of the YAG lattice structure.

Optical and electrical properties of a spiral LED filament

This paper introduces a new type of spiral white light-emitting diodes（WLED） filament with high luminous efficiency and uniform optical performance. The optical and thermal properties of the flexible filament were investigated at different stretching heights, namely 0, 1, 2, and 3 cm. The results indicated that the filament showed the best optical characteristics at the stretching height of 2 cm, because of good heat dissipation. In addition, the radiation temperature of the filament was inversely proportional to the output luminous flux. The reliability of the filament at a stretching height of 2 cm was also evaluated after 1000 h of use. The result demonstrated that the luminous flux decay of the bulb was only 0.85%. The flexible spiral WLED filament exhibiting high luminous flux and good reliability could be adapted to promote industrial development in the near future.

Room-temperature synthesis of cyan CsPb(Cl/Br)3/SiO2 nanospheres with Li Cl-H2O solution

There are many strategies to maintain the excellent photoluminescence(PL) characteristics of perovskite quantum dots(QDs). Here, we proposed a facile and effective method to prepare cyan CsPb(Cl/Br)3/SiO2 nanospheres at room temperature. Cubic CsPb(Cl/Br)3 was obtained by adding a LiCl-H2O solution and anion exchange reaction. With(3-aminopropyl)triethoxysilane as an auxiliary agent, a QDs/SiO2 composite was extracted from a sol-gel solution by precipitate-encapsulation method. The transmission electron microscopy images and Fourier transform infrared spectra indicated the QDs were indeed embedded in silica substances.Besides, humidity stability and thermal stability show the composite possesses a great application value.Finally, cyan QDs@SiO2 powder has a high PL quantum yield of up to 84%;the stable cyan fluorescent powder does have great potential to play a key role in commercial full spectrum display.

Study on the mechanism of color coordinate shift of LED package

In the paper, the influences of the chip, silicone and phosphors on the color coordinate shift of LED were studied. In the process of LED baking, it was found that the effect of the chip and silicone on the color coordinate drift is less than 3% through the analysis of each influencing factor. But the influence of the phosphors is large and accounted for 11.11% of the overall impact factors. Therefore, it is important to select the better green phosphors in thermal stability for the LED package and it has a guiding significance to the color coordinate of LED distribution.