| With the worldwide scarcity of resources and increasingly serious environmental pollution,the search for a green,environmentally friendly and sustainable new energy source has become particularly important.White light emitting diodes(w-LEDs)is regarded as an excellent lighting source with small size,long life and low energy consumption.At present,the more mature technology is to use blue LED chips to excite the YAG:Ce3+ yellow phosphor combination to generate white light,however,the white LEDs obtained by this method lack red components,resulting in higher color temperature and lower color rendering index of the light-emitting devices,which seriously restricts their development and application.Therefore,it is particularly important to develop red light-emitting materials that can be efficiently excited by near-ultraviolet light and can also emit light stably.In recent years,the bicalcite-type oxides A2B’B"O6 have attracted a lot of attention from researchers as a matrix material for phosphors.Located at the B’ and B" sites,is coordinated with six O atoms to form the[B’O6]and[B"O6]octahedral structures,respectively,which provide a suitable crystal field substitution environment for the radius-matched luminescent central ion.For this reason,Sr2GdNbO6(SGNO)was chosen as the substrate of the luminescent material and Eu3+ and Mn4+ as the excitation ions in this thesis to investigate its fluorescence properties.The results show that the light-emitting material based on SGNO is a very efficient and new light-emitting material with excellent thermal stability.The main content of this thesis contains the following 3 aspects:(1)A series of SGNO:xMn4+(x=0.003～0.01)phosphors were prepared by high-temperature solid-phase method,their crystal structure,luminescence properties and thermal stability were investigated in detail.The synthesized phosphors have a monoclinic crystal structure with a space group of P21/c.The doped manganese replaces Nb5+ in the matrix SGNO with the chemotactic state of Mn4+,forming a phosphor with a single crystal structure.x=0.4 mol%for the optimal doping of Mn4+,and the SGNO:Mn4+ phosphor shows strong red light emission at 666 nm under 360 nm photoexcitation.This emission peak corresponds to the 2Eg→4A2g energy level jump of Mn4+,the quantum yield is 46.6%.It has good thermal stability in the temperature range of 303～463 K.The fluorescence lifetime decreases gradually with the increase of Mn4+doping concentration,and the chromaticity coordinate points are all located in the red edge region,and the luminescence color purity reaches 97%.It is a new type of red light-emitting material with great development potential.(2)A series of SGNO:xEu3+(x=0.04,0.06,0.08,0.10,0.12)phosphors were synthesized by high-temperature solid-phase reaction method,and detailed study of luminescence performance,thermal stability and quantum efficiency.The doped europium replaced the Gd3+in the matrix SGNO with the chemotactic state of Eu3+ to form a phosphor with a single crystal structure.SGNO:xEu3+ phosphor exhibited red-orange emission under both blue λex=468 nm and near-UVλex=395 nm excitation,with the main emission peaks centered at 622 nm and 593 nm.The main emission peaks are located at 622 nm and 593 nm,which are attributed to the 5D0→7F2 and 5D0→7F1 energy level jumps of Eu3+,respectively.When the doping amount of Eu3+ is x=8 mol%,the luminescence quantum efficiency of blue-light excitation reaches the highest value of 16%.The effect of the temperature(295-568 K)on the fluorescence intensity and quantum efficiency under dual-wavelength excitation was analyzed,and it was found that the phosphor not only had a high quantum efficiency but also a higher thermal stability under blue light λex=468 nm excitation.The average fluorescence decay lifetime of the sample SGNO:0.08Eu3+ under blue light excitation was 0.841 ms,and the color coordinates were(0.648,0.368),and the luminescence color purity reached 93%,which is a new red fluorescent material with potential application in dual wavelength response.(3)A new red fluorescent material of SGNO:0.004Mn4+,xEu3+(x=0.06,0.08,0.10,0.12)was prepared by high-temperature solid-phase method.The thermal stability and optical properties of the target products were characterized and analyzed in detail.The strongest red light emission was exhibited when the Eu3+ doping concentration was 8 mol%.Since the thermal responses of Mn4+and Eu3+are different,and the thermal burst of Mn4+fluorescence intensity is much faster than that of Eu3+with increasing temperature,so its temperature characteristics were explored by the fluorescence intensity ratio(FIR)of Eu3+to Mn4+,and the results show that the maximum relative sensitivity of phosphor reaches 0.780%K-1 in the temperature range of 298～518 K,which is better than other temperature sensing materials.Therefore,the study of SGNO:Mn4+,Eu3+phosphors is of great importance in the field of both solid-state lighting and optical thermometry. |
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