BaGd_0·5(PO₄)₂: Eu_0·5³⁺ and ABaGd_0·5(PO₄)₂: Eu_0·5³⁺ (where A⁺=Li, Na or K) double phosphates were synthesized by solid state diffusion method. These powders were characterized using X-ray diffraction (XRD) and scanning electron microscopy (SEM) techniques. XRD results showed many distinct lines in the XRD spectra. SEM measurement showed grains of different sizes in double phosphates. The Eu³⁺-ion emission lines for⁵D₀→⁷F_j (j=1, 2, 3, and 4) transitions showed a splitting into 3, 2, 1, and 2 components, respectively. Strength of these lines was enhanced by the addition of alkali ion to BaGd_0·5(PO₄)₂: Eu_0·5³⁺ double phosphate. However, as the alkali ion varied from Li⁺ to K⁺, the intensity of⁵D₀→⁷F₂ line (617 nm) in the red region increased at the cost of⁵D₀→⁷F₁ line (599 nm) in the orange region. Suitable explanation has been proposed for this phenomena.

Optical properties of rare earth-activated Ca$_3$(PO$_4$)$_2$:RE (RE = Eu$^{3+}$ and Dy$^{3+}$) phosphors obtained by wet chemical synthesis method, are reported in this paper. The phase confirmation of synthesized phosphor host is done by X-ray diffraction study. SEM images of the sample host reveal irregular morphology with collection of particles and porous nature. The crystal structure is not viewed with naked eyes, although particle size ranges from 2–5 micrometres. Photoluminescence characterization of Ca$_3$(PO$_4$)$_2$:Eu$^{3+}$ gives characteristic orange–red emission at wavelengths of 594, 613 and 617 nm upon near UV excitation at 397 nm attributed to ${}5$D$_0$ ${\rightarrow}$ ${}7$F$_1$, ${}7$F$_2$ transition of rare earth Eu$^{3+}$ ion. Whereas Ca$_3$(PO$_4$)$_2$:Dy$^{3+}$ gives blue–yellow emissions at wavelengths 483 and 574 nm due to near UV excitation at wavelength of 351 nm, which are corresponding to ${}4$F$_{9/2}$ ${\rightarrow}$ ${}6$H$_{15/2}$, ${}6$H$_{13/2}$ transitions of dopant ion Dy$^{3+}$. Colour coordinates from CIE diagram of 483 and 574 nm are obtained at (x = 0.0781, y = 0.1704) and (x = 0.471, y = 0.527) for the Ca$_3$(PO$_4$)$_2$:Dy$^{3+}$ phosphor. Whereas in the case of Ca$_3$(PO$_4$)$_2$:Eu$^{3+}$ for an emission wavelength of 613 nm, the colour coordinates are found to be (x = 0.674, y = 0.325). The presented optical investigation of phosphor displays that the reported phosphor can be a potential contender for ecofriendly solid-state lighting.

This article reports photoluminescence in Eu$^{3+}$ and Dy$^{3+}$ doped Ca$_2$SrAl$_2$O$_6$ aluminate phosphor. Here combustion technique is used to synthesize a series of phosphors. The excitation spectra of Ca$_2$SrAl$_2$O$_6$:Eu$^{3+}$phosphor appears at 396 nm, under which we get a prominent emission bands at 590–596 nm and another peak located at 616 nm that corresponds to the orange-red region. These spectral bands are assigned due to ${}^5$D$_0$${\rightarrow}$${}^7$F$_1$, 7F2 electronic transitions of activator Eu$^{3+}$ ion, respectively. Whereas, Ca$_2$SrAl$_2$O$_6$:Dy$^{3+}$ phosphor shows two bands that correspond to 476 and 573 nm when excited by 352 nm. These two emission peaks correspond to the well-known ${}^4$F$_{9/2}$${\rightarrow}$${}^6$H$_{15/2}$, ${}^6$H$_{13/2}$ transitions of rare-earth Dy$^{3+}$ ion, respectively. Thus, from the observed photoluminescence properties, it is seen that prepared aluminate phosphor may be a suitable material for solid-state lighting.

The BiPO$_4$:Ln (Ln = Dy$^{3+}$, Tb$^{3+}$ and Sm$^{3+}$) phosphor were prepared using wet chemical synthesis and studied its photoluminescence properties. Under 352 nm excitation, the BiPO$_4$:Dy$^{3+}$ phosphor shows the blue (481 nm)and yellow (575 nm) emissions due to the ${}^4$F$_{9/2}$ ${\rightarrow}$ ${}^6$H$_{15/2}$ and ${}^4$F$_{9/2}$ ${\rightarrow}$ ${}^6$H$_{13/2}$ transitions of the Dy$^{3+}$ ion, respectively. When BiPO$_4$:Tb$^{3+}$ phosphor was excited at 378 nm, it emits efficient narrow green emission at 545 nm due to ${}^5$D$_4$ ${\rightarrow}$ ${}^7$F$_5$ transition. The BiPO$_4$:Sm$^{3+}$ phosphor shows yellow, orange and red emissions centred at 598 nm, which is attributed to the ${}^4$G$_{5/2}$ ${\rightarrow}$ ${}^6$H$_{7/2}$ transition of the Sm$^{3+}$ ion. The CIE coordinates indicate that the prepared phosphors have high colour purity. The photoluminescence results suggests that BiPO$_4$:Ln (Ln = Dy$^{3+}$, Tb$^{3+}$ and Sm$^{3+}$) phosphor may be used as a possible material for near-UV-based solid-state lighting.