Site Occupancy Preference, Enhancement Mechanism, and Thermal Resistance of Mn⁴⁺ Red Luminescence in Sr₄Al₁₄O₂₅: Mn⁴⁺ for Warm WLEDs

Abstract

Red phosphors play an indispensable role in phosphor-based warm white light emitting diodes (WLEDs). We demonstrated recently that the non-rare-earth phosphor Sr 4 Al 14 O 25 :Mn 4+ exhibits red luminescence even more intensely than the commercial Mn 4+ phosphor 3.5MgO.0.5MgF 2 .GeO 2 :Mn 4+ upon blue excitation. Herein, on the basis of crystal field calculations employing the exchange charge model, we identify the energy levels of three types of Mn 4+ ions situated at Al 3+ sites in the Sr 4 Al 14 O 25 crystal lattice and find that the doped manganese ions occupy preferentially the Al4 and Al5 more highly covalent sites rather than the Al6 site. We report that the Mn 4+ luminescence can be enhanced upon the inclusion of Mg 2+ in the synthesis reaction.The mechanisms for this effect comprise the lower nonradiative decay rate from the 2 E g state due to the reduction in energy migration along Mn 4+ ions to killer sites and also the morphology evolution from orderly layered smooth nanosheets to irregular nanoparticles disorderly compacted in porous bundles. Interestingly, various other phases are formed upon the addition of Mg 2+ . The resistance of Mn 4+ photoluminescence in the phosphor to thermal impact has also been studied and no obvious thermal degradation after a cycle experiment by heating and cooling the sample between 25 o C and 300 o C was found. As proof of concept, a warm perception WLED has been made when the phosphor was applied to the package of a blue LED chip and YAG:Ce.

Photoluminescence properties of a novel red fluoride K2LiGaF6:Mn4+nanophosphor

“…Currently most of the available red phosphors still have certain problems. 10,11 For example, oxide phosphors [12][13][14][15][16] cannot absorb blue light efficiently and sulde phosphors [17][18][19] are unstable because of their high sensitivity to hydrolysis reactions. As for the nitride phosphors, [20][21][22][23] they have overlapping re-absorption with the yellow phosphor and the synthesis conditions are rigid.…”

Phosphor coated NiO-based planar inverted organometallic halide perovskite solar cells with enhanced efficiency and stability

“…Such a phosphor exhibits higher intense red luminescence than that of the commercial Mn 4+ phosphors due to the inclusion of Mg 2+ . 32 Fig. 1a depicts the device architecture for the NiO-based CH 3 NH 3 PbI 3 solar cell with coating on the top of FTO glass and the corresponding molecular structure of SAM.…”

“…This is attributed to the typical emission of Mn 4+ . 32,33 The internal quantum efficiency was measured to be 38 and 35% for the excitation wavelengths of 380 and 470 nm, respectively, for the SAM film. 32 The inset of Fig.…”

“…32,33 The internal quantum efficiency was measured to be 38 and 35% for the excitation wavelengths of 380 and 470 nm, respectively, for the SAM film. 32 The inset of Fig. 1b shows an optical image of a phosphor film (on quartz) illuminated by UV light at λ~360 nm, exhibiting a uniform red emission over the entire area.…”

Synthesis and characterization of Ca3Lu(GaO)3(BO3)4:Ce3+,Tb3+ phosphors: tunable-color emissions, energy transfer, and thermal stability

“…[1][2][3][4] In the lighting industry, white light-emitting diodes (w-LEDs) have many advantages in lighting applications, such as having long working lifetimes and high luminous efficiency, and being energy-saving and environment-friendly, which meet the requirements of saving energy and protecting the environment. [5][6][7][8][9][10] At present, two methods have been used to fabricate the w-LEDs; one is combining a blue InGaN chip with commercial yellow phosphor Y 3 Al 5 O 12 :Ce 3+ , and the other is using an ultraviolet/near ultraviolet (n-UV; 350-420 nm) LED chip and tricolor (red, green, and blue) phosphors.…”