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In this paper, a novel cryolite-type up-conversion luminescent material K 3 Sc 0.5 Lu 0.5 F 6 : Er 3+ , Yb 3+ with controllable crystal form was synthesized by a high temperature solid state method. K 3 Sc 0.5 Lu 0.5 F 6 : Er 3+ , Yb 3+ can crystallize in monoclinic or cubic form at different temperatures. The composition, structure and up-conversion luminescence (UCL) properties of K 3 Sc 0.5 Lu 0.5 F 6 : Er 3+ , Yb 3+ samples with different crystal form were investigated in detail. It is impressive that both monoclinic and cubic forms of K 3 Sc 0.5 Lu 0.5 F 6 : Er 3+ , Yb 3+ show green emission ( 2 H 11/2 / 4 S 3/2 → 4 I 15/2 ). The luminescence intensity of cubic K 3 Sc 0.5 Lu 0.5 F 6 is much higher than that of the monoclinic form, and the reasons are also discussed in detail. The results show that the luminescence intensity of up-conversion materials can be effectively tuned by controlling the crystal form. According to the power dependent UCL intensity, the UCL mechanism and electronic transition process were discussed. In addition, the fluorescence decay curves were characterized and the thermal coupling levels (TCLs) of Er 3+ ( 2 H 11/2 / 4 S 3/2 → 4 I 15/2 ) in the range of 304-574 k were used to study the optical temperature sensing characteristics. All the results show that K 3 Sc 0.5 Lu 0.5 F 6 : Er 3+ , Yb 3+ can be used in electronic components and have potential application value in temperature sensing fields., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

Cryolite is a suitable host for up-conversion luminescent materials due to its low phonon energy and good optical transparency. In this work, a novel up-conversion material K 3 YF 6 :Yb 3+ , Er 3+ with a cryolite structure was prepared successfully by a solid state method. The crystal structure, morphology, composition and up-conversion luminescence properties of the as-prepared sample were characterized by X-ray diffractometry (XRD), field emission scanning electron microscopy (SEM) and fluorescence spectrometer in detail. K 3 YF 6 :Er 3+ , Yb 3+ has a cryolite structure. Under 980 nm excitation, the as-prepared sample can generate slight green emission at 524 and 546 nm (attributed to 2 H 11/2 → 4 I 15/2 transition, 4 S 3/2 → 4 I 15/2 transition of Er 3+ ) and strong red emission at 661 and 672 nm (corresponding to 4 F 9/2 → 4 I 15/2 transition, 4 I 9/2 → 4 I 15/2 transition of Er 3+ ). All the green and red up-conversion emission of K 3 YF 6 :Er 3+ , Yb 3+ transfer and electronic transition process of the red and green light the sample emitted, the possible luminescence mechanism is discussed in this paper., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

In recent years, compounds with a cryolite structure have become excellent hosts for luminescent materials. In this paper, Tb 3+ doped and Tb 3+ /Eu 3+ co-doped K 3 LuF 6 phosphors were prepared via a high temperature solid phase sintering method. The XRD, SEM, as well as photoluminescence excitation (PLE) and emission (PL) spectra were measured to investigate the structure and luminescence properties of the as-prepared samples. In the Tb 3+ /Eu 3+ co-doped K 3 LuF 6 samples, both characteristic emission spectra of Tb 3+ and Eu 3+ could be observed and the emission color of the K 3 LuF 6 :0.12Tb 3+ , x Eu 3+ phosphors could be adjusted from green to yellowish pink and the corresponding CIE values could be regulated from (0.2781, 0.5407) in the green area to (0.4331, 0.3556) in the yellowish pink area by controlling the concentration ratio of Eu 3+ /Tb 3+ . In addition, the energy transfer mechanism in Tb 3+ /Eu 3+ co-doped K 3 LuF 6 was calculated to be a quadrupole-quadrupole interaction from Tb 3+ to Eu 3+ based on the Dexter's equation., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

In this study, we investigated the structure, luminescence properties and morphology of La 6 Ba 4 (SiO 4 ) 6 F 2 :Dy 3+ in detail using X-ray diffraction (XRD), photoluminescence spectroscopy, scanning electron microscopy (SEM) and decay kinetics measurements. The results indicate that La 6 Ba 4 (SiO 4 ) 6 F 2 :Dy 3+ was well crystallized, and its structure is of apatite-type and belongs to the hexagonal system. The prepared samples exhibit two intense characteristic bands in the blue (484 nm) and yellow (579 nm) spectral ranges corresponding to the Dy 3+ transitions 4 F 9/2 → 6 H 15/2 and 4 F 9/2 → 6 H 13/2 , respectively. These dominant photoluminescence bands are accompanied by a weak red band (670 nm) due to the 4 F 9/2 → 6 H 11/2 transition. The emission color of La 6 Ba 4 (SiO 4 ) 6 F 2 :Dy 3+ phosphors are found to fall in the white light region. The Dy 3+ optimal dopant concentration in the La 6 Ba 4 (SiO 4 ) 6 F 2 host was found to be 0.12 (mol). In addition, the phosphors have high thermal stability. Hence, La 6 Ba 4 (SiO 4 ) 6 F 2 :Dy 3+ may have an application in white light-emitting diodes., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

The Ba 2 La 2.85- x Tb 0.15 Eu x (SiO 4 ) 3 F (BLSOF:0.15Tb 3+ , x Eu 3+ ) multicolor phosphors with apatite structure were synthesized via the solid-state pathway. The crystal structure and luminescence properties of the phosphors were investigated by means of scanning electron microscopy (SEM), X-ray diffraction (XRD), Rietveld refinement, photoluminescence excitation (PLE) and photoluminescence (PL). The luminescence performance of the phosphor was optimum when the concentration of Tb 3+ was set to be 0.15 mol and the concentration of Eu 3+ was set to be 0.22 mol. Under the accurate excitation of 373 nm near ultraviolet (n-UV) light, the emitting color of the phosphors can be tuned from green to red with increasing Eu 3+ /Tb 3+ ratio. It was further proved that the quadrupole-quadrupole (q-q) interaction is responsible for the energy transfer (ET) in the BLSOF:0.15Tb 3+ , 0.22Eu 3+ phosphor. Owing to the excellent thermal quenching luminescence property, the BLSOF:0.15Tb 3+ , x Eu 3+ phosphor can be applied in n-UV white light emitting diodes (w-LEDs) and serve as the warm part of warm white light., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)