Enhancement of photoluminescence in Eu 3+ co-activated Ca 2 MgSi 2 O 7 :Dy 3+ phosphors for solid state lighting application

An attempt to enhance the afterglow luminescence of NIR light emitting long persistent phosphor Zn3Ga2Ge2O10:Cr3+ by Pr3+ co-doping

In this study we have focused on the improvement of luminescence intensity and the long afterglow luminescence of Cr³⁺ doped Zn₃Ga₂Ge₂O₁₀ long persistent phosphor by adding an appropriate amount of Pr³⁺ ions in proportion with Ga concentration. We have successfully developed a series of long persistent Zn₃Ga_(2-x-y)Cr_xPr_yGe₂O₁₀ (where x = 0, 0.04 and y = 0, 0.01, 0.02, 0.03, 0.04) phosphors by high temperature solid state reaction method. The structural properties of the developed phosphors were characterized by X-ray diffraction method. The diffuse reflectance spectra were recorded at room temperature and it shows three strong absorbance bands at the wavelength of 256, 412 and 570 nm due to the transitions of ⁴A_2g→⁴T_1g (4P), ⁴A_2g→⁴T_1g (4F) and ⁴A_2g→⁴T_2g (4F) of Cr⁺³ ions which are also confirmed from the photoluminescence (PL) excitation spectra. PL emission analysis revealed that developed phosphors have a strong narrow luminescence around 698 nm and significantly enhanced with the Pr³⁺ content upto its optimum value (0.02). Afterglow NIR light emission from the developed phosphors was captured by night vision monocular and it is found that the phosphors have long persistent luminescence for more than 24 h. Thermoluminescence (TL) measurement was also carried out for better understanding the kinetic mechanism and luminescence process in these materials. This will enable to calculate the trapping parameters associated with prominent glow peaks.

Enhanced emission intensity in (Li+/Ca2+/Bi3+) ions co-doped NaLa(MoO4)2: Dy3+phosphors and their Judd-Ofelt analysis for WLEDs applications

In the present study, we have synthesized a series of Dy3+ ion doped NaLa(MoO4)2phosphors by the conventional solid-state method at 750 °C for 4h. All the compounds were crystallized in the tetragonal scheelite type structure with space group (I41/a, No.88). The morphology and functional group were confirmed by the field emission scanning electron microscopy (FE-SEM) and Fourier transform infrared(FTIR)spectroscopy. Upon near-Ultraviolet (n-UV) excitation, the PL spectra exhibit the two characteristic emissions of Dy3+ ions, blue (4F9/2→6H15/2) at 487 nm and yellow (4F9/2→6H13/2) at 574nm respectively. The optimum concentration of Dy3+ionis 3 mol% and then quenching occurred due to multipolar interaction. Further, enhanced the emission intensity by co-doping with monovalent (Li+), divalent (Ca2+) and trivalent (Bi3+) ions. Among them, Li+ ion co-doped samples are shown maximum intensity (50 times) more than Dy3+ doped phosphors as relaxation of parity restriction of electric dipole transition because of local distortion of crystal field around the Dy3+ ions. In addition, by incorporation of Eu3+ ions into NaLa(MoO4)2:Dy3+system, tuned the emission color from white to red, owing to energy transfer from Dy3+ to Eu3+ ions. The intensity parameters (Ω2, Ω4) and radiative properties such as transition probabilities (AT), radiative lifetime (rad), and branching ratio were calculated using the Judd-Ofelt theory. CIE color coordinates, CCT values indicates that these phosphors exhibit an excellent white emission. The determined radiative properties, CIE and CCT results revealed that the Dy3+-activated NaLa(MoO4)2phosphors are potential materials for developing white LEDs, and optoelectronic device fabrications.

Research progress of Mn doped phosphors

In this review article, Mn applications have been divided into three parts.