Shinan He

Luminescent properties of Eu3+-doped α-NaYF4 single crystal under NUV-excitation

Abstract This paper reports on successful synthesis of α-NaYF4 single crystal doped with Eu3+ at various concentrations by a modified Bridgman method. The crystal structure is characterized by means of X-ray diffraction. The absorption spectra, excitation spectra and emission spectra were measured to investigate the optical properties of the single crystals. An intense red emission located at 611 nm with long lifetime of 9.03 ms was observed in single crystal under the excitation of 394 nm light. It benefits from the low maximum phonon energy of α-NaYF4 single crystal matrix (390 cm−1). The CIE chromaticity coordinate of the α-NaYF4 single crystal doped Eu3+ in 4 mol% concentration was calculated (x = 0.6055, y = 0.388), which was close to the National Television Standard Committee standard values for red phosphor (x = 0.67, y = 0.33). All these spectral properties suggest that that this kind of fluoride crystal with high thermal stability and high efficiency of red emission may be used as potential red phosphors for optical devices.

Highly efficient up-conversion luminescence in Er 3+ /Yb 3+ co-doped Na 5 Lu 9 F 32 single crystals by vertical Bridgman method

Er3+/Yb3+ co-doped Na5Lu9F32 single crystals with different concentrations of Yb3+ ions were prepared to investigate their phase structure, up-conversion (UC) properties and mechanism of UC luminescence by Bridgman method. Under 980 nm near-infrared (NIR) excitation, three sharp UC emission bands topping at green ~525 nm, ~548 nm and red ~669 nm were obtained in Er3+/Yb3+ doped Na5Lu9F32 single crystals which are attributing to the transitions of 2H11/2 → 4I15/2, 4S3/2 → 4I15/2 and 4F9/2 → 4I15/2, respectively. The quadratic dependence of pump power on UC emission indicated that two-photon process is in charge of the transition from excited state of Yb3+ ions to lower state of Er3+ ion in Na5Lu9F32 single crystals. The long-accepted mechanism for the production of red and green emissions through up-conversion (UC) under 980 nm excitation in Er3+/Yb3+ co-doped materials apply in the Na5Lu9F32 host was displayed. The enhancement of the red emission was observed due to a cross-relaxation (CR) process of the form: 4F7/2 + 4I11/2 → 4F9/2 + 4F9/2. Furthermore, an ideal yellowish green light performance could be achieved with 1.0 mol% Er3+ doped certain Yb3+ concentrations samples, and its external quantum efficiency approached to 6.80% under 5.5 Wcm−2 980 nm excitation which can be applied in developing UC displays for electro-optical devices.

Infrared spectroscopic characterization of Na5Lu9F32 single crystals doped with various Er3+ concentrations

Abstract This work reports on optical spectra of Na5Lu9F32 single crystals doped with various Er3+ concentrations from 0.5 to 5 mol%. In our improved Bridgman method, the X-ray powder diffractions were investigated and optical parameters were also calculated by the Judd–Ofelt theory. Results showed that Er3+ ions entered the Lu3+ sites successfully without causing any obvious peak changes, and the doping concentration of Er3+ had important influence on the Er3+ local structure in Na5Lu9F32 crystals. The maximum emission intensities of ~1.5 and ~2.7 μm were obtained in present research when the doping concentration of Er3+ were 4 and 5 mol%, respectively, under the excitation of 980 nm LD. In these doping concentration, the maximum emission cross-sections were calculated to be 1.37 × 10−20 cm2 (~1.5 μm) and 2.1 × 10−20 cm2 (~2.7 μm). The gain cross-section at 2.7 μm was also estimated according to the absorption and emission cross section spectra. All these spectroscopic characterizations suggested that this fluoride crystal would possess promising applications in infrared lasers.