Phosphor Opto-Thermal Modeling And Applications In White LD/LED Packaging

With the advantages of high luminous efficiency,long lifetime,and environmental protection,light-emitting diode(LED)has been considered as the fourth-generation light source and widely applied in lighting and display fields.However,the efficiency of LED decreases under high electrical power density.In contrast,laser diode(LD)can maintain higher efficiency under high electrical power density and possesses low source etendue.As a result,LD is gradually replacing LED in some high-luminance lighting fields,e.g.,the vehicle headlight,the projector and so on.Phosphor is a vital part in white LED/LD packaging.The particle diameter,geometry,concentration,and packaging form of the phosphor layer affect the overall optical and thermal performances,which are,respectively,determined by the light propagation and thermal transport processes.In addition,when the excitation optical energy density is high(e.g.,white LD),the local high temperature and even phosphor thermal quenching happen easily in low-thermal-conductivity phosphor layer,where there is an interaction between the optical performance and thermal performance.Therefore,a deep understanding of the light propagation,thermal transport processes and the interplay between them will contribute to the development of the packaging process of the white light sources with high optical-thermal performances.Based on this point,we established optical and opo-thermal model of phosphor,and developed packaging methods for white LD with high optical and thermal performances.The achievements are as follows:1)The radiance variation of all light propagation processes in the phosphor layer,including the light absorption,anisotropic scattering,and fluorescence,were described quantitatively in theory.Based on radiative transfer equation(RTE),we established the extended fluorescent radiative transfer equation(FRTE).In addition,the light-to-heat process and phosphor thermal quenching effect were described quantitatively.2)A two-wavelength one-dimensional phosphor optical model for remote white LED packaging was established.The spectral element method was applied to solve FRTEs for the blue and yellow lights and the general boundary conditions,where the radiance distributions of the blue and yellow lights and the optical performances were obtained.Based on the twowavelength model,we established a multi-wavelength optical model by considering the excitation spectrum,emission spectrum,and the re-absorption effect.Using this model,we can obtain the spectrum.In addition,we experimentally verified both models.3)A two-dimensional axisymmetric opto-thermal phosphor model for remote white LD packaging was established.The discontinuous spectral element method was applied to solve the FRTEs in the cylindrical coordinate system and the general boundary conditions,in which case the radiance distributions of the collimated and diffuse blue and yellow lights were calculated.Then,we introduced the temperature-dependent phosphor quantum efficiency and iteratively solved FRTEs and heat diffusion equation,where the opto-themral performances could be predicted more accurately.We also experimentally validated the model.By using the model,we evaluated the key parameters of the white LD packaging.4)Based on the opto-thermal model,we proposed two packaging methods for white LD with high optical-thermal performances.a)A secondary optics consisting of a modified parabolic reflector coupled with a freeform lens was.Using this optics,a high ACU within small view angle was achieved.b)A double-sided reflective phosphor cooling process was proposed.The phosphor temperature was reduced greatly without affecting the optical performacnes,leading to a higher limiting excitation power and color stability.