Design And Synthesis Of Several Typical Luminescent Materials For Lighting/Display

Phosphor-converted white light emitting diode（pc-WLED）shows the advantages of high efficiency,strong reliability,energy saving and environmental protection,which can meet the rapidly-updated and diverse needs for health lighting and intelligent display.The combination of LED chip and phosphor is the main strategy to obtain white light,and thus,the performance of phosphor directly determines the quality of pc-WLED devices.In the field of lighting,there are still some practical problems such as low color rendering index,serious reabsorption between various materials,“cyan cavity in full-spectrum”,“blue light hazard”,etc.In the field of phosphors for LED backlight in liquid crystal display,commercial greenβ-Sialon:Eu²⁺phosphor is widely used,but problems such as wide emission peak width at half height,low luminous efficiency,harsh synthesis conditions,and so on,are not solved.In addition,the domestic industry has no independent intellectual property rights forβ-Sialon:Eu²⁺,and there are only a few other green narrow-band phosphors for the industry to choose.Therefore,high-efficiency blue phosphors that match well with near-ultraviolet LED chips,wide-band cyan phosphors that cover both blue and green light bands are of great significance for improving the quality of pc-WLED and developing healthy lighting.The development of novel green-emitting phosphors with narrow band to obtain wide-color-gamut LED backlight has become a major concern of researchers and relevant enterprises.In this paper,high-efficiency phosphor for illumination were obtained by cation substitution,the close relationship between crystal structure and luminescence properties was studied in depth.Based on the requirements of narrow-band emitting phosphors for high rigidity of crystal structure and high symmetry of cationic lattice,novel narrow-band phosphors with green emission were designed by selecting appropriate hosts and activators to satisfy the requirements of phosphor performances for wide-color-gamut LED backlights.The specific works are as follows:（1）A series of blue Ba_0.47-xSr_0.50+xAl₂Si₂O₈:0.03Eu（x=-50.0%～47.0%）phosphors with the narrowest FWHM of 73 nm,a maximum quantum efficiency of 82.3%and excellent thermal stability have been designed through selecting Ba_0.5Sr_0.5Al₂Si₂O₈with single large-radius cation as the host and Eu²⁺as the activator ion.These phosphors can be efficiently excited by near-ultraviolet（n-UV）light.By changing the Sr/Ba ratio,the transformation of Ba_0.5Sr_0.5Al₂Si₂O₈monoclinic barium feldspar structure to Ba Al₂Si₂O₈hexagonal nepheline or Sr Al₂Si₂O₈feldspar structure is realized,which indirectly regulates the local environment of the luminescence center,and the symmetry of polyhedral transformation from“m”to“6/mmm”or“1”were realized.Compared with Ba_0.5Sr_0.5Al₂Si₂O₈:Eu²⁺,the peak position Ba_0.47-xSr_0.50+xAl₂Si₂O₈:0.03Eu（x=-50.0%～47.0%）series samples show a blue shift of 17 nm or red shift of 24 nm.The internal quantum efficiency can be increased by 10%and the full width at half maximum can be narrowed by 13 nm.The thermal stability can be improved with the decrease of crystal structure symmetry.Based on the fine crystal-structure analysis,the synergistic effect of crystal-phase transition and polyhedron transformation on luminescence performance was revealed.（2）Through cation-substitution strategy,Ba and Y lattice in Ba Y₂Si₃O₁₀:Eu were replaced by different types of RE³⁺（RE=Lu,Gd,Yb）and M²⁺（M=Mn,Mg,Zn）to regulate the average lattice,local structure and electronic microenvironment of Eu²⁺.A series of broad-band cyan emission phosphors,Ba Y_2-x/y/zRE_x/y/zSi₃O₁₀:Eu and Ba_0.97-x/y/zM_x/y/zY₂Si₃O₁₀:Eu were obtained owing to the redistribution of Eu²⁺in the lattice.Based on the comprehensive analysis of local and average crystal structure,cation order degree and electronic microenvironment,the corresponding theoretical models of“the intensification effect of the second luminescence centre”and“the concentration perturbation effect”were established.The relationship between crystal structure and luminescence properties was clarified.The white LED device was fabricated by coating mixture of cyan Gd/Lu/Yb/Mg/Mn phosphor and red Ca Al Si N₃:Eu²⁺on a 365nm LED chip.Its color rendering index value is even higher than 90 and correlated color temperature is lower than 5500 K,indicating that high-quality warm white light is realized.The cyan cavity can be weakened by using the wide-band cyan-emitting phosphors.（3）A green phosphor Sr₄Al₁₄O₂₅:Ce³⁺,Tb³⁺that can be excited by near ultraviolet light was designed.The main emission peak of the phosphor is located at 544 nm,and full width at half maximum is about 9.65 nm,which is attributed to the ⁵D₄-⁷F₅transition of Tb³⁺.Via the sensitization effect of Ce³⁺,the absorption for UV light in the range of 350-400 nm is significantly enhanced,the luminescence intensity is increased by more than 10 times,and the decay time is reduced to 1.95 ms.When heated to 423K,the luminescence intensity of the phosphor remains 82.21%of that at room temperature,and the thermal quenching temperature exceeds 523 K,indicating a weak thermal quenching behavior.white LED lamps were fabricated by using a 350 nm near-UV LED chip coated with the narrow green Sr₄Al₁₄O₂₅:0.16Ce³⁺,0.08Tb³⁺,commercial blue Ba Mg Al₁₀O₁₇:Eu²⁺and red K₂SF₆:Mn⁴⁺phosphors.The color gamut is calculated to be 85.34%NTSC,comparable to that of theβ-Si Al ON:Eu²⁺-converted devices（82%NTSC）reported in the literature.The dominant interaction during the energy transfer from Ce³⁺to Tb³⁺in the Sr₄Al₁₄O₂₅:Ce³⁺,Tb³⁺system is confirmed to be the dipole-dipole interaction and the ET efficiency is as high as 85%.（4）Two novel green phosphors,Ba Zn Al₁₀O₁₇:0.20Mn²⁺and Sr Mg Al₁₀O₁₇:0.30Mn²⁺with ultra-narrow-band were designed through introducing Mn²⁺into Ba Zn Al₁₀O₁₇and Sr Mg Al₁₀O₁₇with high symmetric crystal structure.Under450 nm excitation,Ba Zn Al₁₀O₁₇:0.20Mn²⁺exhibits green emission peaking at 516 nm,with full width at half maximum of 31 nm,internal quantum efficiency of 85.59%,color purity of 78%,and fluorescence lifetime of 5.21 ms.Ba Zn Al₁₀O₁₇:0.20Mn²⁺phosphors show weak thermal quenching behavior.The energy loss is only 5%at 423K and the luminescence intensity at 473 K still remains 90%of the initial intensity at room temperature.Sr Mg Al₁₀O₁₇:0.30Mn²⁺shows a green emission peak at 517 nm with a half-peak width of 28 nm.The internal quantum efficiency of hexagonal block morphology samples with 5 wt%H₃BO₃as flux reaches 86.6%and has better thermal stability.The white LED devices fabricated with blue LED chips,narrow-band green phosphor Sr Mg Al₁₀O₁₇:0.30Mn²⁺/Ba Zn Al₁₀O₁₇:0.20Mn²⁺,red K₂Si F₆:Mn⁴⁺can achieve 114%NTSC and 110%NTSC,respectively.Some performances are superior to that of the white LED device withβ-Sialon:Eu²⁺as green light.