Study On Synthesis, Luminescence Properties And Microstructure Of Novel (oxy)Nitride Green Phosphor For White LEDs

Five novel (oxy)nitride phosphors for white LEDs were synthesized by solid-state reactionmethod, and their structures, spectral characteristics, thermal quenching and quantum efficiencyand microtopography were systematically researched.Pure phase Ba3Si6O12N2:Eu2+was synthesized under a reducing N2/H2atmosphere bycontrolling Si/Ba and O/Ba ratios. This green phosphor exhibited a small thermal quenching andhigh quantum efficiency. The emission intensity remained90%of the initial when measured at200°C. The internal and external quantum efficiencies measured under450nm excitation were68and38%, respectively. The emission wavelength of (BaSr)3Si6O12N2:Eu2+was tunable by Sr2+substituting part Ba2+. However, the emitting-color of Ba3Si6-zAlzO12+zN2-z:Eu2+was inflexibledespite part Si-N substituted by Al-O. Besides, crystal defects increased when Al-O replaced Si-N,causing declining emission intensity. The particle morphology became irregular and seriousagglomeration with Al-O content increasing. Color temperature tunable, from3110K to6440K,white LEDs with a high color rendering index of Ra=88~94were attained by combining the as-prepared Ba3Si6O12N2:Eu2+and a commercial red phosphor Sr2Si5N8:Eu2+with a blue LED chip.The green phosphor, Si6-zAlzOzN8-z:Eu2+, was synthesized under high-pressure N2atmosphere.The influence of z values on its luminescence properties and micro-topography was discussed.When z<0.2or z>2.5, this phosphor, excited under UV, emitted strong blue light as influenced byAlN and other impurities. When0.2≤z≤2.5, this phosphor emitted strong green light. When zvalues were increased, the particle morphology, from SEM images, presented a change of fromequiaxied to rodlike, to irregular shape, and the sizes of particles were from1~2μm to20~30μm.The critical distance Rcof energy transfer between Eu2+was calculated to be24.5. The emittingwavelengths of Si6-zAlzOzN8-z:Eu2+was tunable by adjusting z values and Eu2+concentration.Two complex sturcture Sr-sialon phosphors, Sr3Si13Al3O2N21:Eu2+and Sr5Al5+xSi21-xN35-xO2+x:Eu2+(x≈0), were obtained under high-pressure N2atmosphere. The photoluminesenceproperties, thermal quenching, quantum efficiency and particle morphology of both phosphorswere reaseached.The emission spectrum of Green nitride phosphor γ-AlON:Mn2+presents with a narrow bandwith a single peak at515nm, which is due to the4T1(4G)â†'6A1transition of Mn2+. The excitationintensity, under230~350nm, of Mn2+-Ce3+co-doped γ-AlON improved greatly. Under280nmexcitation, the emission intensity of Mn2+-Ce3+co-doped γ-AlON increased60times comparing with Mn2+single-doped. The optimal Ce3+concentration of Mn2+-Ce3+co-doped γ-AlON was5mol%, and the critical distance Rcof dipole-quadrupole energy transfer between Mn2+and Ce3+was calculated to be20.2. The excitation and emission intensity of Mn2+-Mg2+co-doped γ-AlON was much higher than that of Mn2+doped γ-AlON, which reasons are considered that Mg2+contribute to doping of Mn2+and nonradinative energy transfer between Mg2+and Mn2+iseffective. Doping Li+or adding MgF2flux can improve the emission intensity of Mg2+-Mn2+co-doped γ-AlON.