The Study Of Luminescence And Thermal Stability Of Cr³⁺ Doped Oxide Phosphors For LED

The development of phosphor converted light-emitting diode technology（pc-LED）greatly promotes the green solid-state lighting and display industries.With the research of the visible light,far-red and near-infrared（NIR）light has attracted widespread attention in industry and science,which can be used in plant lighting,treatment of physical diseases,automotive sensors,and biological non-destructive testing.Transition metal Cr³⁺doped luminescent materials usually emit far-red and NIR,because they are easily influenced by crystal field environment,and are potential candidates for far-red and NIR spectral range.Compared with fluoride,sulfide,and other compounds,the oxide system matrix is one of the preferred research systems because of its stable physical and chemical properties.In addition,the operating temperature of the LED device can reach 150°C,the luminous intensity of the phosphor inevitably produces a thermal quenching phenomenon.Therefore,exploring the luminescence properties and temperature-dependent properties of Cr³⁺doped oxides are of practical significance for the pc-LED.In this paper,three phosphors are prepared by the traditionalhigh-temperaturee solid-state method,and the pure crystalline phase and the valence state of chromium ions are proved by the X-ray powder diffraction,X-ray photoelectron spectroscopy,and Electron paramagnetic resonance spectroscopy,other main contents are as follows:ZnGa₂O₄:Cr³⁺far-red oxide phosphor presents R line origin from the spin forbidden transition of²E→⁴A₂.Due to the distortion of the ZnGa₂O₄ host,the ²E energy level is split into ²E（ē）和²E（2ā）,divided into R1 and R2 lines.The luminescence decay curves of the ZnGa₂O₄:Cr³⁺sample show lifetimes changing from 5.83 ms to 2.16 ms in the range of 140–440 K.At the same time,the temperature sensing relative sensitivity increases with the elevation of temperature and reaches the maximum value of 0.582%K^-1 at 400 K.Lu₂Ca Al₄Ge O₁₂:Cr³⁺oxide phosphor shows far-red luminescence.A broad excitation band in the 400-500 nm region was found in the excitation spectrum,which matches well with the chip that emits blue light.Therefore,under the excitation of 428 nm,the phosphor exhibits a mixed band of R-line emission ²E→⁴A₂ and broad emission ⁴T₂→⁴A₂ of Cr³⁺ions.In the temperature range of 300-620 K,the overall emission intensity reaches about 109%at 420 K and maintains 81.4%at 620 K compared to the value at 300 K,and the electrons derived from the ²E and ⁴T₂ energy levels are thermally activated and repopulated.Al₆Ge₂O₁₃:Cr³⁺exhibits near-infrared broadband emission at 600-1000 nm.The integrated emission intensity of Al₆Ge₂O₁₃:3%Cr³⁺at 420 K can keep 81%of that at 300 K,demonstrating good luminous thermal stability.Finally,this phosphor is combined with a 430 nm blue light chip to prepare a near-infrared pc-LED device,which presents a peak position of 780 nm and the full width at half the maximum of 160 nm in the electroluminescence spectrum.Besides,the near-infrared output power is 81.7 m W at 300 m A,and internal quantum efficiency reaches 72.84%.