Study On Luminescence Properties Of Manganese(?)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.