**1. Introduction**

The growth of good quality larger area thin film with homogeneous size distribution and morphology is still a demanding issue, and it is of significant attention towards the research fraternity. Remarkably, uniform micro/nano-structures have been paying global attention due to its potential application in high-performance luminescence and opto-electronic device based

© 2016 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2016 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

on community their novel optical and electronic properties. To synthesize novel thin film materials such as molybdates [1, 2], tungstates [3], vanadates [4], and fluorides [5], copious prominent techniques are extensively adopted, for example chemical bath deposition (CBD), successive immersion layer adsorption reaction (SILAR), polymerization, electrodeposition, sputtering, metal-organic chemical vapour deposition (MO-CVD), molecular beam epitaxy (MBE), atomic layer deposition (ALD), pulsed laser deposition (PLD). In the midst of all, PLD is a multitalented method to prepare multiconstituent thin film materials in which raster examining of high-energy pulsed laser ablates the target material and produces the plasma plume [6, 7]. In recent times, the PLD technique has created a widespread usage with an exceptionally astonishing result in materials preparation and fabrication of a device in the optoelectronics field. Albeit the fabrication of optical quality of the thin films and waveguides using PLD technique with various technical hitches and burning issues, till date, these issues have undeniably been lucratively conquered, and quite a few good-quality thin films were grown by PLD.

### **1.1. Recent research scenario**

In contrast to conventional incandescent and fluorescent lamps, white light emitting diode (w-LEDs) is seemed to be an optimistic solid-state light source with a good-quality energy conversion luminescence device [8]. By coalesce into the GaN blue LED chip with yellow emitting phosphor YAG:Ce3+ which yield a white light emission using the conventional technique [9–11]. Nevertheless, the deficient of red emission cog ends with low colour rendering index (CRI) and luminous efficacy of radiation (LER) which restricts their pertinence towards a few ambits [9, 12]. To conquer this hindrance, red or orange-red emitting ion such as Pr3+, Sm3+, Cr3+ and Mn2+ is co-doped with YAG:Ce3+ [10]. The other one is combining YAG:Ce3+ with red or orange-red phosphors such as nitrides (M2SiN8:Eu2+), sulphides (CaS:Eu2+), oxynitrides (MSi2O2N2:Eu2+) (where M = Ca, Sr) [10]. Furthermore, the enhancement of intense emission in the host material can be engendered by co-doping of alkali metalchloride results in strong emission, which may possibly be an opportune and a generally suitable approach to acquire the phosphors with sufficient intensity and excellent efficiency are a great essential deal for prospective solid-state lighting devices [2]. Therefore, it is necessary to discover a suitable phosphor material with a sufficient chemical permanence with enhanced efficiency. Rare earth-doped phosphor materials are paying attention towards the research problems based on its applications in all the prospects of science and technology. Molybdates and tungstates with metallic elements form an essential class of phosphor materials. They belong to the scheelite family having a space group I41/a. In both molybdate and tungstate family, the alkaline earth-based rare-earth-activated double molybdates are very much highly significant efficient materials on the basis of its unique structural, optical properties have come across profound applications in technological aspects. Alkaline rareearth-activated tungstates having a general formula ARE (MoO4)2 (RE = Y, La; A = Ba, Ca, Sr) are considered as better luminescent hosts investigated significantly for various purposes such as photocatalysts [11], displays [8] and acquire substantial hydrolytic and thermal permanence. Furthermore, the electroluminescent devices in the form of thin films from these micro/ nano-architectures are to be built for the white light emitting diode applications. Among the aforesaid variety of fabrication of thin film techniques, pulsed laser deposition (PLD) is a viable method [2, 13, 14]. Nowadays, to fabricate homogeneous and large-scale thin films, laser rastering system attached into PLD technique has been used [13]. To consider the aspects of application, aforesaid reasons could make the PLD technique most unique and almost suitable for the growth and fabrication of good-quality micro/nano-thin films. It is interesting that the structural, optical, and photophysical properties of the micro/nano-architectures could be compared with the thin film phosphors and its bulk [2, 15] counter-parts.

In this viewpoint, we have prepared the single crystalline nano-thin phosphor films of Ca0.5R1 *<sup>x</sup>*(MoO4)2:*x*Ln3+ (R3+ = Y, La), (Ln3+ = Eu, Tb, Dy) with co-doping of alkali metal chlorides (0.02  M of LiCl, KCl, NaCl) have been ablated on quartz substrates using the pulsed laser deposition method (PLD). For the first time, the luminescence properties of these alkali chloride-activated phosphors are studied. The as-prepared molybdate and tungstate powders were further deposited as thin films using the laser-ablation by forming a ceramic target under oxygen atmosphere. Followed by the as-prepared samples was analyzed using X-ray diffraction (XRD), atomic force microscopy (AFM), field emission scanning electron microscopy (FESEM), photoluminescence (PL) spectroscopy, photometric characteristics using commission internationale de i'eclairage (CIE) diagrams. The colour chromaticity coordinates and luminescence decay times have also been determined and discussed in reference to the effect of alkali metal ions.
