**4. Conclusion**

The representative PL decay curves for luminescence emission for the phosphors Ca0.5Y1-

are shown in **Figure 12a**, **b**. This can be fitted well into a single exponential function [15, 27]

t

where *I*0 is the luminescence intensity at times *t* = 0 and *τ* is its associated luminescence lifetime.

**Phosphor CCT (K) CRI Colour coordinates LER (lm W-1) Colour purity (%)** *τ* **(ms)**

Ca0.5Y(MoO4)2:Eu3+,Na+ 1149 33 0.635 0.365 162 90.0 0.462 Ca0.5Y(MoO4)2:Tb3+,Na+ N/A 26 0.296 0.564 491 87.5 0.455 Ca0.5Y(MoO4)2:Dy3+,Na+ 3658 18 0.414 0.478 525 81.3 0.172 Ca0.5La(MoO4)2:Eu3+,Na+ 1196 42 0.656 0.343 321 95.0 0.481 Ca0.5La(MoO4)2:Tb3+,Na+ 6850 12 0.251 0.570 530 91.9 0.485 Ca0.5La(MoO4)2:Dy3+,Na+ 4195 16 0.404 0.485 462 81.7 0.187

**Table 1.** Photometric parameters, color purity and luminescence decay time for the phosphors Ca0.5R1-*x*(MoO4)2:*x*Ln3+,

The thin phosphor films grown from nano-powder are being synthesized by the hydrothermal method, and the synthesis procedure is described previously by our group [17]. The luminescence emission intensity is being enhanced by co-doping of alkali metal ions. Furthermore, for the co-doping of alkali precursors, instead of using alkali chloride, alkali carbonates were taken and converted them into alkali nitrates. These alkali nitrates were co-doped with the existing precursors following the hydrothermal method nano-powders were synthesized and thin films were deposited from these powders [17]. The room temperature PL emission spectrum for Ca0.5R1-*x*(MoO4)2:*x*Eu3+,Na+ (R = Y, La) as the representative thin phosphor films are shown in **Figure 14**. The emission spectra monitored at 395 nm UV excitation for both the phosphors shows a number of intra-configurational ff transitions. The strong and most intense emission peak is found at 616 nm for Ca0.5Y1-

*x*(MoO4)2:*x*Eu3+,Na+ and 615 nm for Ca0.5La1-*x*(MoO4)2:*x*Eu3+,Na+ is attributed to the 5

electric-dipole transition possess hypersensitive red emission [15, 28, 29]. The Stark energy splitting is mildly shown for both the phosphors. It is noticed that the splitting of the electric dipole transition is uniform and homogeneous between the two thin phosphor films. The intensity of the spectral peaks for the nano-thin phosphor film is nearly close

**3.4. Photoluminescence emission studies from nano-architectures**

(Ln = Eu, Tb and Dy)

D0 → <sup>7</sup> F2

è ø (2)

(Ln = Eu, Tb and Dy) and Ca0.5La1-*x*(MoO4)2:*x*Ln3+,Na+

48 Applications of Laser Ablation - Thin Film Deposition, Nanomaterial Synthesis and Surface Modification

0exp *<sup>t</sup> I I*

The photometric quantities and luminescence decay time values are given in **Table 1**.

*x y*

æ ö - <sup>=</sup> ç ÷

*x*(MoO4)2:*x*Ln3+,Na+

as

Na+

(R = Y, La; Ln = Eu, Tb and Dy).

In conclusion, the nano-sized single crystalline Ca0.5La1-*x*(MoO4)2:*x*Eu3+,M+ ceramic thin phosphor films deposited on quartz substrates by pulsed laser deposition technique using Nd-YAG laser source in an ultra-high vacuum (UHV). The FESEM images exhibited the sphericalshaped phosphor particles. XRD patterns revealed the scheelite-type crystal structure without any impurity phases. By using AFM, the surface topographies and distributions of grains were investigated. Upon optical excitation, Eu-, Tb, and Dy-doped Ca0.5La1-*x*(MoO4)2:*x*Eu3+,M+ thin phosphor films showed characteristic emissions in the bright-red, green and yellow regions, respectively. The obtained results suggested that the deposited thin film phosphors could serve as efficient materials for electroluminescence and display applications.
