Study On Luminescence Properties Of Manganese(Ⅳ)activated Deep-red Tungstate Phosphors

With the advent of fluorescent lamps,phosphors with photoluminescence characteristics have been playing an important role in people’s lighting needs.Among them,red phosphor not only plays a significant role in improving the color rendering index and reducing color temperature of LEDs,but also indispensable in indoor plant cultivation.At present,the commercial red phosphor mostly uses rare-earth Eu³⁺(Eu²⁺,Ce³⁺,etc.)ions with fewer reserves and expensive as activator.In order to change this situation,we use Mn⁴⁺ions with abundant reserves as activators and tungstate as matrix material to carry out the following work:（1）The methods of increasing the luminous intensity of Ca₃La₂W₂O₁₂:Mn⁴⁺phosphor are explored.In term of process optimization,adding pre sintering process（1100oC,2h）can effectively increase the uniformity of the samples.In addition,we also research the effect of non-activator element doping on the luminescence performance of the samples.Finally,it is found that the luminous intensity of phosphors can be nearly doubled when Ti⁴⁺,Zr⁴⁺,Ge⁴⁺and Sn⁴⁺are added properly.It is worth noting that the doping of Ti⁴⁺,Zr⁴⁺,Ge⁴⁺and Sn⁴⁺does not change the shape and position of the original excitation and emission spectra.The improved Ca₃La₂W₂O₁₂:Mn⁴⁺phosphor is expected to be used for plant growth lamps in the field of plant cultivation.（2）Mn⁴⁺ doped Ba₆Y₂W₃O₁₈ and Ba₆Gd₂W₃O₁₈ phosphors of double perovskite structure have been synthesized via solid-state reaction method at high-temperature.Excitation spectra show the phosphors have broad excitation band in region of300-600 nm with four Gaussian fitting bands peaking at around 331 nm,366 nm,440nm and 518 nm for Ba₆Y₂W₃O₁₈:Mn⁴⁺and peaking at around 347 nm,374 nm,436nm and 511 nm for Ba₆Gd₂W₃O₁₈:Mn⁴⁺.Far-red emission band locates at 693 nm for Ba₆Gd₂W₃O₁₈:Mn⁴⁺.The difference of the crystal field strength and nephelauxetic substitution between Y³⁺and Gd³⁺induced variation of luminescence properties might give meaningful reference for designing new Mn⁴⁺-doped phosphor or regulating its luminescence performance.（3）A novel Mn⁴⁺-activated Ba₃Y₂WO₉ phosphor of double perovskite structure has been prepared via high-temperature solid-state reaction method.The phosphor can emit red emission located at～692 nm,which greatly overlaps with the absorption spectra of chlorophyll and phytochrome in the red light range.the intensest excitation band of the phosphor originating in the O^2-→Mn⁴⁺charge transfer and the ⁴A_2g→⁴T_1gof Mn⁴⁺centres at～367 nm,while the sub intense excitation band formed by ⁴A_2g→⁴T_2g transition is located in the yellow-green light region（～535 nm）.The excitation and emission performance of the phosphor indicates its potential application in light-conversion film/glass for greenhouse cultivation since it can convert not only UV but also yellow-green light into red emission.The optimal doping concentration of Mn⁴⁺in the Ba₃Y₂WO₉ host is 0.3 mol%,beyond which energy transfer between Mn⁴⁺ions based on d-d interaction results in fluorescence quenching.Besides,the crystal field strength and thermal stability of the sample are also discussed.