Until very recently the MASER could only be used in very specialist applications such as radio astronomy. The reason for this is that cryogenic cooling and to a lesser extent, high applied magnetic fields, prohibited mass production on the grounds of both complexity and cost. Despite the fact that the MASER was discovered before the LASER these issues meant that the latter, which does not need applied magnetic fields or cooling, saw widespread adoption in a huge range of applications from bar-code readers, laser discs to laser eye surgery. In 2013 Imperial and UCL were awarded an EPSRC funded research project to produce a room temperature MASER. Although we had preliminary observations that room temperature masing was possible we had not verified this in a different laboratory setting, nor did we have a clear idea of how the masing molecule interacted with light and which crystal orientations or dopant concentrations would be optimal. This collaboration was remarkably successful achieving all the objectives we set. Now, in what is another world first, the team has constructed a diamond MASER capable of continuous-wave operation at room temperature. Our previous research has concentrated solely on organic materials as the masing medium. In this proposal we will explore the potential of masing in inorganic materials at room temperature. In doing so we will obviate two key problems encountered with organics. Problem 1 - Decay rates: The primary obstacle that prevents continuous operation in organics is the relatively long lifetime of the lowest triplet sub-level, reducing the number of pentacenes available for optical pumping (bottleneck) and destroying the population inversion. Problem 2 - Heating: The organic gain medium, pentacene in p-terphenyl we first used to demonstrate a room temperature MASER cannot withstand a continuous illumination by a laser because the temperature of the terphenyl host rises above its melting point. Solution to both problems: a radical but exciting departure which will address both problems simultaneously is to explore high spin states in inorganic materials with high melting/decomposition temperature and favourable thermal conductivities (T.C.): such as diamond (M.P. 3550C; T.C. 2000 W/mK) and silicon carbide (2730C; T.C. 120 W/mK). Very recently we observed masing at room temperature in diamond exploiting NV centres. This means we can build upon a huge wealth of research in the UK and elsewhere on diamond NV centres. Again there is much research exploring defects in SiC that we can build on. We have initiated a collaboration with the group of Prof. Dr. Vladimir Dyakonov at Würzburg group who are currently exploring SiC. REF. https://arxiv.org/pdf/1709.00052.pdf Achieving this would further establish without doubt the UK as the key place to carry out fundamental research on the topic of room temperature MASERs.