Guoqi Zhang

Analysis of photoluminescence mechanisms and thermal quenching effects for multicolor phosphor films used in high color rendering white LEDs

In order to prepare phosphor-converted white LEDs with high color rendering index (CRI) and high luminous efficiency, the multicolor phosphor film by mixing more than two monochromatic phosphor powders in a silicone matrix is widely used. But usually its photoluminescence mechanism cant be explained by a simple superposition of each spectra emitted by individual monochromatic phosphors. Additionally, as being close to LED chips, the phosphor film is always suffered under high temperature when LED operates. Therefore, this study analyzes the thermal quenching effects of multicolor phosphor films prepared by mixing the Garnets, Silicates and Nitrides based phosphors in silicone. And their photoluminescence mechanisms are investigated by modeling of spectral power distributions (SPDs) for the prepared white LED chip scale packages (CSPs) through optical simulations with LightTools software. Through analyzing the features of emission spectra (e.g. emission peak, peak wavelength and full widths at half maximum (FWHMs)) from prepared multicolor phosphor films, the results show that the heat treatment leads to a significant decrease of luminous intensity, all peak wavelengths shift to the short-wavelength range and all FWHMs become narrow. However, these results are not simply the superposition of each thermal quenching effect of monochromatic phosphors and this nonlinearity is supposed to be caused by the reabsorption of luminescence between phosphor particles and multiple conversions among them.

Lumen and chromaticity maintenance lifetime prediction for LED lamps using a spectral power distribution method

In this study, a spectral power distribution (SPD) based method is developed to analyze and predict reliability characteristics of Light Emitting Diode (LED) lamps, such as lumen and chromaticity maintenance lifetimes. Usually, an entire SPD of a LED lamp can be regarded as the superposition of an asymmetric blue with a phosphor converted spectrum, each of which can be fitted by an Asymmetric Gaussian (AGaussian) model. During the ageing process, the decomposed SPD model parameters extracted from the test data of a LED lamp are fitted further to an exponential degradation model. Then at any given time, the lumen maintenance φ and color coordinates u and v can be calculated by predicting the SPD of a LED lamp. In order to demonstrate the application of the proposed method, a batch of ten LED PAR20 lamps equipped with four phosphor converted white LEDs (pc-white LEDs) were aged at 25 °C for 4000 hours. And a statistical analysis was performed to calculate the median values (50 percentile) of φ and duv with both upper boundary (5 percentile) and lower boundary (95 percentile). The results show that most of the measured φ and duv can be enveloped within the lower boundary curves predicted by the proposed model. In addition, there is a good prediction result of the φ curves by using the proposed method and a published statistical method. At last, the comparison between lumen and chromaticity maintenance lifetime predictions shows that the luminous flux depreciation failure may be the primary concern than the color shift in the selected test samples.

Prediction of Lumen Depreciation and Color Shift for Phosphor-Converted White Light-Emitting Diodes Based on A Spectral Power Distribution Analysis Method

The spectral power distribution (SPD) is considered as the figureprint of a light emitting diode (LED). Based on the analysis on its SPD, a method to predict both lumen depreciation and color shift for the phosphor converted white LEDs (pc-LEDs) is proposed in this paper. First, the entire SPD of a pc-LED is predicted by superimposing two asymmetric double sigmoidal (Asym2sig) models, which represent the decomposed blue light and phosphor converted light peaks, respectively. For a better understanding of how the SPD model affects the photometric and colorimetric characteristics of a pc-LED, a sensitivity study of the SPD parameters is then performed on its luminous flux <inline-formula> <tex-math notation=LaTeX>

Cause analysis on highly depreciated indoor LED product in CSA020

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Phosphor–silicone interaction effects in high power white light emitting diode packages

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Fatigue failure modeling of wire bonds of high power LED packages with a multiphysics simulation method

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Prediction of a statistical distribution of luminous flux for LED modules with an analytical model

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A POF based breakdown method for LED lighting color shift reliability

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Validation of the methodology of lumen depreciation acceleration of LED lighting

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A degradation model of aluminum electrolytic capacitors for LED drivers

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