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Mn-based phosphors with the wavelength of 700–750 nm are an important category of far-red phosphors that have promising potential in the application of plant lighting, and the higher ability of the far-red light emitting of the phosphors is beneficial to plant growth. Herein, a series of Mn4+- and Mn4+/Ca2+-doped double perovskite SrGd2Al2O7 red-emitting phosphors with wavelengths centered at about 709 nm were successfully synthesized by means of a traditional high-temperature solid-state method. First-principles calculations were conducted to explore the intrinsic electronic structure of SrGd2Al2O7 for a better understanding of the luminescence behavior in this material. Extensive analysis demonstrates that the introduction of Ca2+ ions into the SrGd2Al2O7:Mn4+ phosphor has significantly boosted the emission intensity, internal quantum efficiency, and thermal stability by 170%, 173.4%, and 113.7%, respectively, which are superior to those of most other Mn4+-based far-red phosphors. The mechanism of the concentration quench effect and the positive effect of co-doping Ca2+ ions in the phosphor were extensively explored. All studies suggest that the SrGd2Al2O7:0.1%Mn4+, 11%Ca2+ phosphor is a novel phosphor that can be used to effectively promote the growth of plants and regulate the flowering cycle. Therefore, promising applications can be anticipated from this new phosphor. [ABSTRACT FROM AUTHOR]

• A Ho3+:KBGM crystal with good quality and large size was successfully grown by using TSSG method. • Crystal structure, polarized absorption and emission spectra were extensively studied. • The crystal has wide absorption and emission bandwidth with large absorption and emission cross-sections. • The lifetime was investigated and result indicated a relatively high quantum efficiency in this crystal. A Ho3+:KBGM crystal with good quality and large size was successfully grown via TSSG method. The crystal's structure, ambient-temperature polarized absorption and emission spectra and fluorescence lifetime were studied. The J-O theory was adopted to analyze the absorption spectra and results show that crystal exhibits relatively large intensity parameters Ω 2 and spectroscopic quality factor which is up to 3.12. At 453 nm, the absorption band is the strongest, and the corresponding cross-sections are 21.94 × 10–20 cm2, 26.66 × 10–20 cm2 and 18.56 × 10–20 cm2 for the - X , - Y and - Z polarizations, respectively. The emission spectra also demonstrate the broad and strong emission band at 2030 nm. The FWHMs and cross-sections are 74 nm, 0.37 × 10−20 cm2, 50 nm, 0.68 × 10−20 cm2, and 49 nm 0.52 × 10−20 cm2 for the three polarizations, respectively. In addition, the crystal has a superior quantum efficiency which is as high as 97.1%. Taking all the analyses into account, it is reasonable to assert that the Ho3+:KBGM crystal an ideal candidate for ∼2 µm laser applications in many areas. [ABSTRACT FROM AUTHOR]

A well-shaped Er3+:KBaGd(MoO 4) 3 (Er3+:KBGM) crystal with the size of 48 × 38 × 15 mm3 was grown by the flux method and, its structure, morphology and optical properties were studied. The first principal calculations on the band structure and density of states of the crystal were also conducted. The important spectroscopic parameters of the Er3+:KBGM crystal were calculated and analyzed by Judd-Ofelt theory. The polarized stimulated emission spectra were investigated by F-L method. The results of up-conversion spectra analysis revealed that two intense green fluorescence bands centered at 533 nm and 554 nm and a broadened weak red fluorescence band at 665 nm were observed when excited at 981 nm. According to the spectroscopic studies, as well as the analysis of decay time of the 4I 13/2 state, the specific energy transfer mechanism of Er3+ ion in this crystal was elucidated. Laser experiment aiming at 1.55 μm continuous-wave laser was conducted in a plane-plane cavity and, when the optimized transmittance of output couplers was 3%, a maximum of 1.05 W laser emission was acquired with the corresponding slope efficiency of 15.36%. With the combination of all the studies, Er3+:KBGM crystal was proved to be a prominent crystal for the 1.55 μm laser. • A large size and Er3+:KBaGd(MoO 4) 3 crystal with good quality was successfully grown by TSSG method for the first time. • The first principal calculations on the band structure and density of states were conducted. • The polarized absorption and emission spectra, fluorescence lifetimes and up-conversion spectrum were analyzed. • The relationship between the disordered crystal structure and optical properties was discussed. • Laser performances were carried out and a 1.55 μm continuous-wave laser with a maximum power of 1.05 W was realized. [ABSTRACT FROM AUTHOR]