Hi Druh,
1a words like G-rand, U-niversity and I-nstitute all have single letter abbreviations. Gold is often AU (and sometimes “or”, but not here). DIODE can’t really be anything else so it looks like a fodder word, so start to put those pieces together, noting that “invested in” helps with the ordering of the parts. The definition is remainder of the clue (and it’s “illumination” in the learning sense, rather than a light source).
11a parses as 6 (nation), 3 (mountain), 3 (protected place… in a biblical sense, see earlier comments on this). The whole clue then works as the definition. This is sometimes called &Lit (and literally).
Hope that helps.