Light is an electromagnetic (EM) radiation extending from the Ultraviolet (UV) to far infrared (FIR) regions. Visible light is a part of this and it covers a range from 400-750 nm. Almost all the materials absorb/emit electromagnetic radiation when interact with a suitable wavelength. The term Luminescence is the emission of radiation in visible region when excited with a suitable wavelength. The materials which emit luminescence are known as luminescent materials. The luminescence observed in visible region on excitation with light is termed as photoluminescence. The luminescence is divided into two categories namely fluorescence and phosphorescence. An emission of light which takes place immediately (10-6 s. Among the various luminescent materials, phosphor materials are the promising one. They emit very intense luminescence under the excitation source. The phosphor materials contain host matrix and activator ion/ions. Rare earth ions are a good activator and they give emission in ultra-violet (UV) to near infrared (NIR) regions under the excitation source. Further, they shows interesting multi photon emission processes such as, lasing, normal fluorescence (also called downshifting), delayed fluorescence, upconversion (UC), quantum cutting (QC) and multiphoton absorption etc. These unique properties of rare earth ions make them useful in different important areas of such as in the field of lasers, fluorescent bulbs, light emitting diodes, colour display devices, as optical amplifiers, as sensors, in television screens, computer monitors, cathode ray tubes, solar cell, bio-imaging and many other devices. Rare earth doped materials can be synthesized through different methods in short duration with desired shape and size. Upconversion (UC) is a nonlinear process in which low energy photons are converted into high energy photon. The emission from the thermally coupled energy levels of rare earth ions can be used in