Luminescence Chromaticity Character Modulation For White LED

In the field of lighting,Light-emitting diode（LED）,as a new generation solid-state lighting（SSL）source,has become a research hotspot because of its advantages of low energy consumption,high conversion efficiency,long lifetime,small volume,rich color,strong durability,no mercury pollution cheapness and so on.In the past ten years,the constant development of white LED replaced the traditional incandescent lamps,fluorescent lamps.Lighting sources can use in a variety of several color-sensitive application fields,such as hospitals,museums,plant breeding,smart road lighting,indoor lighting and urban landscape lighting.What’s more,it is required for the optical parameters of LED in different situations,such as luminescence efficiency,correlated color temperature,and the color rending index.Therefore,the selection of excellent reliability,thermal stability and adjustable LED light color quality is the key to package white LED.In this paper,silicate phosphors were prepared by high temperature solid state method.The thermal stability,reliability and application in encapsulated LEDs differences of the two phosphors were compared and analyzed.Through the nonlinear distribution law of chromaticity coordinates of 3014 devices,the chromaticity coordinates and correlated chromaticity temperature of composite phosphors with arbitrary mass ratio are obtained by fitting.Experimental verification and theoretical analysis were carried out.The main research work is as follows:（1）The Ca_0.2Sr_2.73 SiO₅: 0.07Eu²⁺ and Ba_0.2Sr_2.73SiO₅:0.07Eu²⁺ phosphors were obtained by conventional high-temperature solid-state method.The tests of X-ray diffraction,energydispersive dispersive spectrometer,scanning electron microscope and their temperature dependent were carried out for the samples.The crystal average particles size is about 15 microns.By mixing BSSO（or CSSO）with Lu2.94Al5O12: 0.06Ce(LuAG: Ce³⁺)phosphors,the converted LED show a white light with the correlated chromaticity temperature in the range of 2500K-5000 K with the highest luminescence efficiency as 153lm/W.（2）In temperature dependent testing,the emission spectral intensity of CSSO phosphors decreased to 97.8%,88.86%,78.4% and 59.2%,respectively.The emission intensity of BSSO increase by 1.83 %,6.14 %,6.51 % and 2.18 % compared with that of CSSO in 323 K,373 K,423 K and 473 K,respectively.The grain surface is corroded increasingly in the accelerated aging tests of thermal cycling,hydrolysis reaction,high temperature and high humidity.In three tests,emission intensity of BSSO enhanced 11.24 %,40.54 % and 20.52 % compared with that of CSSO,separately.The results indicated that BSSO phosphor has higher reliability and thermal stability than CSSO phosphor in a negative external environment for warm LED application.（3）In the experimental group,LuAG: Ce³⁺ and CaAlSiN₃:Eu²⁺ composite phosphors powder with different mass ratios were used to package 3014 devices.With the increase of G: R mass ratio,the correlated chromaticity temperature range of 3014 devices can range from 2500 K to around 8000 K,and the correlated chromaticity temperature coverage range is large.When G: R= 18:1,the maximum value of 144lm/W,the lowest value of 107lm/W,and the chromaticity rendering index was above 88.（4）In the experimental group,chromaticity coordinates of 3014 devices with different proportions were fitted.The chromaticity coordinates distribution characteristics of each proportion of the device are consistent with the quadratic equation of one variable: y = a2 + b1 + c.By comparing the experimental correlated chromaticity temperature with the fitted,it can be obtained that: G: R= 10:1 has a correlated chromaticity temperature difference of 2K.The three coefficients a,b and c corresponding to different mass ratio equations are fitted respectively.It satisfies the conic equation with one variable.This is the mathematical model that we end up with.Five groups of specific experiments were conducted to verify it.The results of the verification group showed that the colorimetric coordinate fitting rule was similar to that of the experimental group.The fitting equation has a unique intersection point with the blackbody radiation line,which still conforms to the characteristics of quadratic equation of one variable,and the fitting degree of the equation is higher than 99%.The difference between the verified group and the fitted correlated chromaticity temperature is compared.The maximum correlated chromaticity temperature difference between the two colors is 173 K,the minimum is 5K,the average difference is 77 K,and the average relative error is 2.567%.The correlated chromaticity temperature difference corresponding to the adjacent mass ratio is about 1000 K.The correlated chromaticity temperature span of the 3014 devices can range from 2,000 k warm white light to 7,000 k cold white light.Obviously,when G: R is 12.1,the corresponding color difference is 15 K,and the correlated chromaticity temperature of the 3014 device is 3375 K.When the correlated chromaticity temperature difference is up to 556 K,the corresponding mass ratio is 16:1:3014 and the correlated chromaticity temperature of the device is 6726 K.Description compared with the 3014 devices with high color,warm and cold white light.The nonlinear mathematical model of chromaticity coordinates is more suitable for low correlated chromaticity temperature white 3014 devices.This is consistent with the fitting results of the experimental group.