Enhancement of red emission and site analysis in Eu2+ doped new-type structure Ba3CaK(PO4)3 for plant growth white LEDs

Abstract

A novel compound Ba3CaK(PO4)3 (BCKP) with new-type structure was synthesized and its structure was determined by X-ray diffraction Rietveld refinement, in which crystal structure consists of Ba1O9, Ba2O12, Ba3O9, CaO8 and KO10 polyhedra, that's five cationic sites. As a phosphor host, Eu2+ doped BCKP emits cold white light with about 90% quantum efficiency (QE) through entering different cationic sites. Based on the results of refinement, three Eu2+ luminescence centers in sites Ca, Ba2 and K were clearly assigned in Eu2+ solely doped BCKP by the time-resolved emission spectra (TRES), Van Uitert equation, but the emissions of Eu2+ at Ba1 and Ba3 sites are not easy to be determined for the same coordination number (CN). According to their different spatial distribution of the coordinated atoms, the first-principles calculation was used to compute the d orbital splitting energy of Eu2+ ions in Ba1 and Ba3 sites to accurately distinguish the ambiguous luminescence centers. In order to meet the requirement of plant growth spectra, Mn2+ was introduced into BCKP: Eu2+ to enhance the red component of spectra, which not only perfectly match with the absorption spectra of carotenoid and chlorophyll-b, but also LEDs fabricated through combining 365 nm near ultraviolet (n-UV) chip with BCKP: Eu2+, Mn2+ phosphor exhibit excellent parameters including high color rendering index (Ra) (92), excellent correlated color temperature (CCT) (4486 K) and outstanding QE up to 65%. Results confirmed that BCKP: Eu2+/Mn2+ phosphor with great potential applications in white LEDs and plant growth. Response to Reviewers: Dear editor, We are pleasure to accept your decision and the reviewers' suggestion. We would like to thank the referees for providing us constructive and valuable queries in bettering our manuscript in the revision. According to the remaining questions of referees, we have answered those questions raised by the referees carefully, and necessary changes have been made in the text. For the received queries, the replies are given below, and the changes in the manuscript have been marked in italic red color letters to show clearly. Reviewers' comments: Reviewer #1: The authors response well to the reviewers' comments and I therefore recommend its publication in Chem. Eng. J. Answer to comments: Thanks for the reviewer's recognition of our answers. Reviewer #3: Compared with the original version, a significant amount of work has gone into the revision of this paper, which has improved it considerably. In my opinion, it is acceptable for publication at its present form. Answer to comments: Thanks for the reviewer's recognition of our answers. Reviewer #9: Question 1: The authors suggested that the results of BCKP structure refinement will convince readers in spite that Biso of cations were over 2 and those for oxygens were over 3. However, as a crystallographer, the suggested crystal structure was less than satisfactory. In addition, the authors discussed the emission properties of BCKP based on the insufficient structure. Answer:...

Luminescence and luminescence quenching of K2Bi(PO4)(MoO4):Sm3+ phosphors for horticultural and general lighting applications

“…19 The pcLEDs, containing far-red Cr 3+ doped gallium garnet, as well as Bi 3+ doped near-UV and Mn 4+ doped far-red Ca 3 Al 4 ZnO 10 , La(MgTi) 1/2 O 3 :Mn 4+ , Ba 3 GdNa(PO 4 )F:Eu 2+ and Ba 3 CaK(PO 4 ) 3 :Eu 2+ ,Mn 2+ phosphors, have already been proposed for horticultural applications. [20][21][22][23][24] The reason Sm 3+ doped phosphor are so attractive for the greenhouse lighting is the fact that they exhibit PL in spectral regions matching the absorption of plant pigments such as chlorophylls a and b as well as phytochrome red (P r ), and far-red (P fr ) residing in the deep-blue (400-460 nm), red (600-680 nm), and far-red (700-740 nm) spectral regions. 25 Another important feature of Sm 3+ doped phosphors is the aforementioned band in the deepred region (around 650 nm), which increases the colour rendition properties.…”

Enhancing photoluminescence properties of Mn4+‐activated Sr4−xBaxAl14O25 red phosphors for plant cultivation LEDs

“…Generally speaking, the demand of plant is divided into blue light (400‐500 nm), red light (600‐690 nm), and far‐red light (700‐740 nm) that corresponding to the photosynthesis, phototropism, and photomorphogenesis of plant, respectively. Therefore, the red and far‐red light regions play a crucial role in the physiological cycle . Therefore, in order to meet the needs of plants for light energy, it is very significance to prepare a kind of high‐performance phosphor that can be strongly absorbed in blue region and emitted in red light for plant cultivation.…”

“…Therefore, the red and far-red light regions play a crucial role in the physiological cycle. [12][13][14] Therefore, in order to meet the needs of plants for light energy, it is very significance to prepare a kind of high-performance phosphor that can be strongly absorbed in blue region and emitted in red light for plant cultivation.…”

Near‐ultraviolet light–induced dazzling red emission in CaGd2(MoO4)4:2xSm3+ compounds for phosphor‐converted WLEDs

“…Apart from the activator, the luminescent host material also has distinct effect on the luminescent properties of the rare‐earth ions‐based phosphors. In general, these inorganic materials that show low phonon energies are preferable for luminescent hosts since they can efficiently decrease the ratio of nonradiative transition and boost the luminescent efficiency . Compared with other developed inorganics, the molybdates with a representative structure of scheelite are considered as potential candidates for luminescent hosts owing to their immanent optical properties (i.e., strong absorption in the ultraviolet [300‐350 nm] region originating from the O 2‒ → Mo 6+ transition) and proper phonon energy .…”

“…In general, these inorganic materials that show low phonon energies are preferable for luminescent hosts since they can efficiently decrease the ratio of nonradiative transition and boost the luminescent efficiency. 12,13 Compared with other developed inorganics, the molybdates with a representative structure of scheelite are considered as potential candidates for luminescent hosts owing to their immanent optical properties (i.e., strong absorption in the ultraviolet [300-350 nm] region originating from the O 2-→ Mo 6+ transition) and proper phonon energy. 14,15 Cao et al revealed that the Sm 3+ -activated LiLaMo 2 O 8 phosphors can emit visible red emission under the excitation of NUV light.…”