Research On The Luminescent Properties Of Transition Metal Ions Activated Red And Near Infrared Phosphors

As the latest generation solid state light source,pc-LEDs（phosphor-converted light emitting diodes,pc-LEDs）,which built on the combination of phosphors and LED chips,have widely used in lighting and display fields.Phosphors,the core components of pc-LEDs,directly determine the spectral quality and energy efficiency of the devices.Benefiting by the unique d-d orbital transitions,transition metal ions activated phosphors have the narrow energy level gaps,which are often used to achieve red and near-infrared（NIR）luminescence.It is of great significance for the construction of high-quality lighting,display devices and novel NIR light sources.Mn⁴⁺activated K₂Si F₆ is one of the most important commercial red phosphors.However,its luminescent performance is easily degraded during the service process owing the moisture erosion.Cr³⁺and Mn⁴⁺have the same 3d³ electron configurations.Located at the weaker crystal field strength,Cr³⁺usually exhibits tunable emissions from deep red to NIR which is considered as the ideal activator for NIR phosphors.In recent years,the emerging fields,such as mechanical vision and NIR detecting techniques,have shown the demand for NIR pc-LED.However,the researches of phosphors are mainly concentrated in the visible region for decades,there exist no products of NIR phosphors.The research is aimed at the two points above,and the specific contents are as follows:1.K₂Si F₆:Mn⁴⁺(KSF:Mn⁴⁺)phosphors with high moisture resistance are successfully constructed via Si⁴⁺-Mn⁴⁺ions exchange and hydrothermal treatment.The luminescent degradation behavior and mechanism are studied systematically.After 6 days of the treatment at 85%humidity and 85 ^oC,the emission intensity of normal KSF:Mn⁴⁺maintains 56%of the initial intensity.KSF:Mn⁴⁺@KSF core-shell structure is constructed via Si⁴⁺-Mn⁴⁺ions exchange and further strengthened by hydrothermal treatment.After 6 days of the treatment at85%humidity and 85 ^oC,the emission intensity of the as-processed KSF:Mn⁴⁺keeps unchanged intensity.2.A novel Ca₃Sc₂Si₃O₁₂:Cr³⁺(CSS:Cr³⁺)NIR phosphor is developed,with a broadband NIR emission covering 700-950 nm.Moreover,Nd³⁺,Yb³⁺and Ce³⁺are introduced to the phosphor to further improve the spectral properties.And a broader emission（covering 480-1100 nm）accompanied with the more powerful NIR intensity is achieved on basis of the energy transfer between these luminescent centers and the high absorption efficiency of Ce³⁺.A super broad pc-LED covering 400-1100 nm is fabricated by integrating the as-prepared phosphor plus the commercial Ca Al Si N₃:Eu²⁺phosphor onto blue LED chip.At the drive current of 100 m A,a total output power of 49 m W with an efficiency of 16%is achieved.3.A series of AMP₂O₇:Cr³⁺（A=Li,Na,K;M=Al,Ga,Sc,In）NIR phosphors are synthesized via high temperature solid state method,and the luminescent mechanism of Cr³⁺in various hosts is developed.Among these NIR phosphors,the emission of Li Sc P₂O₇:Cr³⁺(LSP:Cr³⁺)is completely in the NIR spectral range（750-1100 nm）.Upon blue light excitation,it presents a NIR emission band with emission maxima(λ_max)of 880 nm and FWHM（full width at half maximum）of 170 nm.However,its internal quantum yield（IQY）is low（38%）.Furthermore,the luminescent improvements are achieved by Yb³⁺cooping.The maximum FWHM of 210 nm and IQY of 74%are obtained accompanied with a reduced thermal quenching.The energy transfer processes are quantitatively analyzed revealing that that the improvement of luminescence originates from the energy transfer from Cr³⁺to more efficient and thermally stable Yb³⁺emitters.NIR pc-LEDs are fabricated by combining LSP:Cr³⁺,Yb³⁺with blue LED chips,giving a maximum NIR output power of～36 m W with an efficiency of12%at 100 m A drive current.4.Novel Ga₄GeO₈:Cr³⁺(GGO:Cr³⁺)phosphors are developed,with ultra-broad NIR emissions covering 700-1300 nm.Tunable emissions(λ_max=835-980 nm)are achieved by varying Cr³⁺doping concentration.An IQY of 60%is achieved for GGO:0.02Cr³⁺,with an emission peaking at 850 nm and a FWHM of 215 nm.According to the quantized transient emissions and time-resolved spectroscopic analysis,the origin of the tunable ultra-broad NIR emissions for GGO:Cr³⁺is determined as multiple Cr³⁺emitting centers..A NIR pc-LED based on GGO:0.02Cr³⁺is fabricated,with a NIR output power of 24 m W with and efficiency of 8%at 100 m A drive current.Furthermore,its applications on internal quality nondestructive analysis of fruits are demonstrated.5.Novel MgGa₂O₄:Cr³⁺,F^-(MGOF:Cr³⁺)phosphors are developed.The multiple targets of enhanced absorption of Cr³⁺,spectral red-shift,broaden emission,increased efficiency and thermal stability are achieved via the O/F anion substitution in phosphor host,which provides a new idea to break performance through of the Cr³⁺activated NIR phosphors.The phosphors present excellent overall performance.For MGOF:0.02Cr³⁺covering 650-1250 nm(λ_max=835nm,FWHM=250 nm),an extremely high IQY of 99%and EQY（external QY）of 51%is achieved as well as a good thermal stability of 94%@150 ^oC.By increased Cr³⁺concentration,the EQY is further improved to 61%for MGOF:0.08Cr³⁺accompanied with a red shift emission of 870 nm.The mechanism of high luminescent performance is revealed by local coordination,theoretical simulation and transient emission analysis.At 100 m A drive current,the NIR output power of NIR pc-LED on basis of MGOF:Cr³⁺is 142 m W with an efficiency of 13%.Moreover,the applications on bioimaging,residual reagent detection and chip inspection are achieved.