Patent ID: 9078331
Filing Date: 2015-07-07
Classification: C09K,H01L,H05B,Y02B

Abstract:
1. A method of preparing a light emitting device that produces white light with a stable correlated color temperature (CCT) and stable color coordinates, the method comprising the steps of: providing a blue LED chip and a yellow phosphor with a specific concentration for converting part of blue light emitted from the LED chip to yellow; wherein the LED chip has an initial emission spectrum with a peak wavelength X slightly smaller than a peak wavelength Y of an excitation spectrum of the phosphor; measuring a decay rate of an emission output power of the phosphor from an ambient temperature to a LED junction temperature of about 120° C.; measuring a red-shifted emission spectrum of the LED chip at the LED junction temperature of about 120° C.; calculating a first excitation ability of the blue LED chip according to a combination of the initial emission spectrum of the LED chip and the excitation spectrum of the phosphor, wherein the excitation ability of the LED chip is calculated by the following formulas: where Pexcitation (λ) is the phosphor excitation spectrum; Pbarechip (λ) is the LED chip emission spectrum; and Pbarechip_N (λ) is the normalized LED chip emission spectrum; calculating a second excitation ability of the blue LED chip according to a combination of the measured red-shifted emission spectrum of the LED chip and the excitation spectrum of the phosphor, wherein the excitation ability of the LED chip is calculated by the aforementioned formulas; and determining whether an increase rate of the excitation ability of the LED chip substantially equals a decay rate of emission output power of the phosphor; and if yes, the LED chip is qualified to be packaged with the phosphor to form the light emitting device that produces white light with a stable correlated color temperature (CCT) and stable color coordinates.