In this work Y₃Ga₅O₁₂ doped with 8.7 mol% Cr³⁺ (YGG:Cr) far-red phosphor pellets calcined at 1000, 1200, 1300, and 1400 °C temperatures were synthesized by a simple and low cost sol–gel method. The YGG:Cr pellets were investigated using X-ray diffraction (XRD) and scanning electron microscopy (SEM) and the luminescent properties were studied by measuring diffuse reflection, photoluminescence (PL), PL excitation (PLE) and internal quantum efficiency (QE). The XRD and SEM results have shown that the material becomes more crystalline, uniform and less porous for higher calcination temperatures. XRD results have also shown that the material becomes strained due to the doping with Cr³⁺ ions for the calcination temperature of 1400 °C. The diffuse reflection and PLE spectra have shown three absorption and excitation bands in the UV, blue and red spectral regions. PL was characterized by a broad band in the far-red spectral region that peaked at about 711 nm. QE has shown a strong dependence on the calcination temperature. Furthermore, using the previously synthesized YGG:Cr phosphor powder and a commercial blue InGaN LED, a far-red–blue phosphor converted LED (pcLED) lamp was designed and characterized. Blue–far-red pcLEDs could be used in greenhouses in order to meet the photophysiological needs of plants.

Keywords: Light-emitting diodes, phosphors, photoluminescence, far-red light, sol–gel
PACS: 78.55.Hx, 81.20.Fw, 85.60.Jb

Cr³⁺ LEGIRUOTAS ITRIO GALIO GRANATAS, SKIRTAS KONVERSIJOS FOSFORE ŠVIESOS DIODAMS
Akvilė Zabiliūtė-Karaliūnė^a, Henrikas Dapkus^a, Rokas Paulius Petrauskas^b, Skirmantė Butkutė^b, Artūras Žukauskas^a, Aivaras Kareiva^b
aVilniaus universiteto Taikomųjų mokslų institutas, Vilnius, Lietuva
^bVilniaus universiteto Bendrosios ir neorganinės chemijos katedra, Vilnius, Lietuva

Darbe pristatomos paprastu ir nebrangiu zolių-gelių metodu susintetintos Y₃Ga₅O₁₂ fosforo tabletės, legiruotos 8,7 mol % Cr³⁺ (YGG:Cr) bei iškaitintos 1000, 1200, 1300 ir 1400 °C temperatūrose. YGG:Cr tabletės buvo ištirtos rentgeno spindulių difrakcijos (XRD) bei skenuojančios elektronų mikroskopijos (SEM) metodais, liuminescencinės savybės ištirtos išmatavus difuzinį atspindį, fotoliuminescenciją (PL), PL sužadinimą (PLE) ir vidinę kvantinę išeigą (QE). XRD ir SEM matavimai parodė, kad didinant iškaitinimo temperatūrą, medžiaga tampa kristališkesnė, tolydesnė ir mažiau porėta. XRD rezultatai taip pat atskleidė, kad tabletėje, iškaitintoje 1400 °C temperatūroje, dėl legiravimo Cr³⁺ jonais atsiranda įtempimai. Difuzinio atspindžio ir PLE spektrai atskleidė tris sugerties ir sužadinimo linijas UV, mėlynoje ir raudonoje spektro srityse. PL spektrai parodė, kad PL pasižymi plačia juosta tolimoje raudonoje spektro srityje, kurios maksimumas yra ties maždaug 711 nm. Nustatyta, kad QE stipriai priklauso nuo iškaitinimo temperatūros. Be to, naudojant anksčiau susintetintus YGG:Cr fosforo miltelius ir prekinį mėlyną InGaN šviesos diodą, sukurta ir ištirta mėlyna–tolima raudona konversijos fosfore kietakūnė lempa. Tokia lempa gali būti naudojama šiltnamiuose augalų fotofiziologiniams poreikiams tenkinti.

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